Reactivity of highly Lewis acidic diborane(4) towards pyridine and isocyanide: formation of boraalkene–pyridine complex and ortho-functionalized pyridine derivatives

The reaction of pinB-BMes2 with Xyl-NC and pyridine results in the formation of a pyridine-coordinated boraalkene that exhibits an intense color. In the presence of an excess of pyridine, the ortho C–H bond of pyridine was selectively functionalized.

After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3, 5-trimethoxybenzene (13.7 mg, 81.5 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 4 (51%). Figure S1. The 1 H NMR spectrum of the crude product for the synthesis of 4

Monitoring the stability of 4 in solution by UV-vis spectroscopy
Solids of 4 (11.7 mg, 20.0 µmol) was dissolved in hexane (10.0 mL). An aliquot (1.00 mL) of the resulting solution was diluted to 10 mL with hexane in a volumetric flask two times to prepare a 100 µM solution. The S3 solution was pipetted into a 1 cm quarts cell. For the experiment with pyridine, a 0.300 M hexane solution (10 µL) of pyridine added to 100 µM solution (3 mL) of 4 to prepare a mixture of 4 with 10 eq. pyridine. The decay of the absorption at 648 nm was monitored with UV-vis spectroscopy. Figure S2. Time course for the decomposition of 4 by using UV-vis spectrum of 4 in hexane (monitored with the absorption maximum at 648 nm); red: no additive, blue: with 10 equiv. of pyridine

Monitoring the stability of 4 in solution by 1 H NMR spectroscopy
In a glove box, a freshly prepared benzene-d 6 solution (600 µL) of 4 (5.0 mg, 8.5 µmol) was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectra were recorded at 0, 13, and 24 h. In both aliphatic and aromatic region, decomposition of 4 and formation of 2 as an intermediate were detected.  5-193.9 °C (decomp.); Anal. Calcd for C 38 H 48 B 2 N 2 O 2 : C, 77.83; H, 8.25;N,4.78;Found: C,77.90;H,8.35;N,4.91.

Estimation of NMR yield for the formation of 5
In a glovebox, a pyridine solution (600 µL) of Xyl-NC (10.5 mg, 79.8 µmol ) was added to a pyridine solution (600 µL) of 1 (30.0 mg, 79.8 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (1200 µL) of 1,3, 5-trimethoxybenzene (13.4 mg, 79.8 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 2 (82%). Figure S5. The 1 H NMR spectrum of the crude product for the synthesis of 5

Synthesis of 6
In a glovebox, a pyridine solution (15 mL) of Xyl-NC (349 mg, 2.66 mmol) was added to a pyridine solution (15 mL) of 1 (500 mg, 1.33 mmol) in a 100 mL flask at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be red. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from benzene at room temperature to afford yellow crystals of 6 (88.7 mg, 0.124 mmol, 9%).
Because of the existence of the equilibrium, signals in the 1 H, 11 B, and 13 C NMR spectrum ( 1 H NMR spectrum at room temperature is shown in Figures S6 and S7) could not be assigned as noted in the main text. However, four low-field signals were exchanged their positions upon cooling the CD 2 Cl 2 solution of 6 down to -80 °C ( Figure S8). As judged by HH COSY experiment ( Figure S9), these four signals were divided to two groups and the blue-colored signal decreased its integral ratio upon cooling ( Figure S8). mp 187.9-191.0 °C (decomp.); Anal. Calcd for C 47 H 57 B 2 N 3 O 2 : C, 78.67; H, 8.01;N,5.86;Found: C,78.59;H,7.90;N,6.04.  In a glovebox, a pyridine solution (8 mL) of Xyl-NC (21.1 mg, 161 µmol ) was added to a pyridine solution (8 mL) of 1 (30.0 mg, 79.8 µmol) in a 30 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3, 5-trimethoxybenzene (13.4 mg, 79.8 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 6 (52%). Figure S10. The 1 H NMR spectrum of the crude product for the synthesis of 6 Estimation of NMR yield for the formation of 6 from 5 In a glovebox, a benzene-d 6 solution (200 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a benzene-d 6 solution (800 µL) of 5 (46.8 mg, 79.8 µmol) and in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (300 µL) of 1,3,5-trimethoxybenzene (13.3 mg, 79.1 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 6 (99%). Figure S11. The 1 H NMR spectrum of the crude product for the synthesis of 6 from 5 General procedure for Table 1 In a glovebox, a toluene solution (y/2 mL, y = from General procedure for Table 2 In a glovebox, a toluene solution (y/2 mL, y = from

Estimation of NMR yield for the formation of 7
In a glovebox, a pyridine solution (300 µL) was added to 1 (30.0 mg, 79.8 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.0 mg, 77.3 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 7 (99%).

Synthesis of 4a
In a glovebox, a toluene solution (3 mL) of Xyl-NC (105 mg, 0.798 mmol) was added to a toluene solution (6 mL) of 1 (300 mg, 0.798 mmol) and 3-methoxypyridine (0.4 mL, 3.99 mmol) in a 30 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be blue.  ,8.18;N,4.54;Found: C,75.60;H,8.28;N,4.14.

Estimation of NMR yield for the formation of 4a with 1 equivalent of Xyl-NC
In a glovebox, a toluene solution (300 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a toluene solution (260 µL) of 1 (30.0 mg, 79.8 µmol) and 3-methoxypyridine (40.3 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.4 mg, 79.8 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectra was recorded to estimate the NMR yield of 4a (65%).

S12
Estimation of NMR yield for the formation of 4a with 2 equivalent of Xyl-NC In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a toluene solution (260 µL) of 1 (30.0 mg, 79.8 µmol) and 3-methoxypyridine (40.3 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.3 mg, 79.1 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 2 (44%) and 4a (18%). Figure S14. The 1 H NMR spectrum of the crude product for the reaction of 1 with 2 eq. Xyl-NC and 3methoxypyridine

Synthesis of 4b
In a glovebox, a benzene-d 6 solution (300 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a benzene-d 6 solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and 3-chloropyridine (37.5 µL, 399 µmol) in a 15 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be blue. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H, 11 B, and 13 C NMR spectra of the crude product for the synthesis of 4b was recorded. Since 4b decomposed upon evaporation of solvent, all the effort to isolate 4b was failed. Therefore, we are providing only NMR spectroscopic data for 4b. A few single crystals suitable for X-ray analysis were obtained by recrystallization (-35 °C) of crude product from a reaction with 3chloropyridine as a solvent. 1 H NMR (400 MHz, C 6 D 6 ) d 1.01 (s, 12H, CH 3 of pin), 2.19 (s, 3H, p-CH 3 of

Estimation of NMR yield for the formation of 4b
In a glovebox, a benzene-d 6 solution (300 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a benzene-d 6 solution (260 µL) of 1 (30.0 mg, 79.8 µmol) and 3-chloropyridine (37.4 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.5 mg, 80.3 µmol) was added to the reaction mixture and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 4b (76%). temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 2 (66%) and 4b (26%). Figure S18. The 1 H NMR spectrum of the crude product for the reaction of 1 with 2 eq. Xyl-NC and 3chloropyridine

Estimation of NMR yield for the formation of 4c
In a glovebox, a toluene solution (300 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a toluene solution S16 mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectra was recorded to estimate the NMR yield of 4c (80%). Figure S19. The 1 H NMR spectrum of the crude product for the synthesis of 4c

Estimation of NMR yield for the formation of 4c with 2 equivalent of Xyl-NC
In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a toluene solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and 4-methoxypyridine (42.5 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.5 mg, 80.3 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 2 (50%) and 4a (39%). Figure S20. The 1 H NMR spectrum of the crude product for the reaction of 1 with 2 eq. Xyl-NC and 4methoxypyridine S17
During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be green. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from pentane at room temperature to afford yellow crystals of 5a (340 mg, 0.519 mmol, 65%). Single crystals suitable for X-ray diffraction analysis were obtained by recrystallization from hexane (-35 °C). 1 H NMR (400 MHz, C 6 D 6 ) d 0.94 (br s, 12H, CH 3 of pin), 2.00 (br s,

Estimation of NMR yield for the formation of 5a
In a glovebox, a toluene solution (300 µL) of Xyl-NC (10.7 mg, 80.3 µmol) was added to a toluene solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and 3-trifluoromethylpyridine (45.9 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.3 mg, 79.1 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 5a (79%).

Estimation of NMR yield for the formation of 5b
In a glovebox, a toluene solution (300 µL) of Xyl-NC (10.5 mg, 79.8 µmol) was added to a toluene solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and 3-(methoxycarbonyl) pyridine (54.0 mg, 39.9 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5trimethoxybenzene (13.6 mg, 80.9 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 5b (67%).

Synthesis of 5c
In a glovebox, a toluene solution (2.5 mL) of Xyl-NC (174 mg, 1.33 mmol) was added to a toluene solution (2.5 mL) of 1 (500 mg, 1.33 mmol) and 4-trifluoromethylpyridine (770 µL) in a 30 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be green.
Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from pentane at room temperature to afford yellow crystals of 5c (

Estimation of NMR yield for the formation of 5c
In a glovebox, a benzene-d solution (300 µL) of 1,3,5-trimethoxybenzene (13.1 mg, 78.4 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 5c (72%).
During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be green. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from hexane (-35 °C) to afford yellow crystals of 5d

Estimation of NMR yield for the formation of 5d
In a glovebox, a benzene-d  Confirmation for the formation of 7a-c The reactions above were checked by 11 B NMR spectroscopy and two major signals in the following three experiments were tentatively assigned as 7a-c without isolation of them.

Reaction of 1 with 3-methoxypyridine
In a glovebox, 3-methoxypyridine (42.5 µL, 421 µmol) was added to a toluene solution (558 µL) of 1 (15.0 mg, 39.9 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, an aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 11 B NMR spectra was recorded. In comparison with the 11 B NMR spectrum of 7, we tentatively assigned this species as sp 2 -sp 3 diborane 7a by a coordination of pyridine derivative. 11 B NMR (160.5 MHz, C 6 D 6 ) d 39 (s), 1 (s).

The reaction of 1 with 3-chloropyridine
In a glovebox, 3-chloropyridine (600 µL, 6.39 mmol) was added to a solid of 1 (15.0 mg, 39.9 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, an aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 11 B NMR spectrum was recorded. In comparison with the 11 B NMR spectrum of 7, we tentatively assigned this species as sp 2 -sp 3 diborane 7c by a coordination of pyridine derivative. 11

Synthesis of 9a
In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a pyridine solution (254 µL) of 1 (30.0 mg, 79.8 µmol) in a 15 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be red. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from hexane (-35 °C) to afford yellow crystals of 9a (8.0 mg, 10 µmol, 13%). Because of the existence of the equilibrium, signals in the 1 H, 11 B, and 13 C NMR spectrum could not be assigned as noted in the main text. Therefore, a characteristic signal of pyridine core at 8.42 ppm was used for the estimation of the NMR yield. 11   temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 9a (31%). Figure S30. The 1 H NMR spectrum of the crude product for the synthesis of 9a

Synthesis of 9b
In a glovebox, a toluene solution (300 µL) of Xyl-NC (182 mg, 532 µmol) was added to a toluene solution (900 µL) of 1 (100 mg, 266 µmol) and 3-(methoxycarbonyl)pyridine (70.4 mg, 1.33 mmol) in a 30 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be red. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from hexane (-35 °C) to afford red crystals of 9b (22.7 mg, 29.3 µmol, 11%). Because of the existence of the equilibrium, signals in the 1 H, 11 B, and 13 C NMR spectrum could not be assigned as noted in the main text.
Therefore, a characteristic signal of pinacol moiety at 0.92 ppm was used for the estimation of the NMR yield. 11

Estimation of NMR yield for the formation of 9b
In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.2 mg, 162 µmol) was added to a toluene solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and 3-(methoxycarbonyl)pyridine (54.6 mg, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.6 mg, 80.9 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectra was recorded to estimate the NMR yield of 9b (24%). Figure S33. The 1 H NMR spectrum of the crude product for the synthesis of 9b

Synthesis of 9c
In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a toluene solution (254 µL) of 1 (30.0 mg, 79.8 µmol) in a 30 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be red. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from hexane (-35 °C) to afford red crystals of 3c (10.8 mg, 13.7 µmol, 17%). In this case, we could isolate 9c and characterize all the signals in NMR spectra. A characteristic signal of pyridine core at 8.02 ppm was used for the estimation of the NMR yield ( Figure

Estimation of NMR yield for the formation of 9c
In a glovebox, a toluene solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a toluene solution (260 µL) of 1 (30.0 mg, 79.8 µmol) and 4-trifluoromethylpyridine (46.2 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.8 mg, 82.1 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 9c (22%). S29 red crystals of 9d (10.8 mg, 13.7 µmol, 17%). Single crystals suitable for X-ray diffraction analysis were obtained by recrystallization from hexane at room temperature. In this case, we could isolate 9d and characterize all the signals in NMR spectra. A characteristic signal of pyridine core at 8.13 ppm was used for the estimation of the NMR yield ( Figure SX ,7.67;.N,5.42;Found: C,75.97;H,7.71;N,5.17.

Estimation of NMR yield for the formation of 9d
In a glovebox, a benzene-d 6 solution (300 µL) of Xyl-NC (20.9 mg, 159 µmol) was added to a benzene-d 6 solution (300 µL) of 1 (29.9 mg, 79.5 µmol) and 4-(methoxycarbonyl)pyridine (47.2 µL, 399 µL) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.7 mg, 81.5 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 9d (24%). Figure S36. The 1 H NMR spectrum of the crude product for the synthesis of 9d In a glovebox, a toluene solution (5 mL) of Xyl-NC (173 mg, 1.33 mmol) was added to a toluene solution (10 mL) of 1 (500 mg, 1.33 mmol) and 4dimethylaminopyridine (163. mg, 1.33 mmol) in a 30 mL vial at room temperature.
During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be brown. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from toluene (-35 °C)   In a glovebox, a toluene solution (300 µL) of Xyl-NC (10.4 mg, 79.3 µmol) was added to a toluene solution (600 µL) of 1 (30.1 mg, 80.0 µmol) and 4-dimethylaminopyridine (9.9 mg, 81.0 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.7 mg, 81.5 µmol) was added to residue and the resulting mixture was stirred for 5 min at room temperature.
An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 10 (67%). Figure S40. The 1 H NMR spectrum of the crude product for the synthesis of 10

Synthesis of 11
In a glovebox, a toluene solution (1.5 mL) of Xyl-NC (69.8 mg, 532 µmol) was added to a toluene solution (3 mL) of 1 (200 mg, 523 µmol) in a 15 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be green. Volatiles were removed from the reaction mixture under reduced pressure. The residue was recrystallized from hexane (-35 °C) to afford yellow crystals of 11 (72.8 mg, 124 µmol, 23%). Single crystals suitable for X-ray diffraction analysis were obtained by recrystallization from hexane at room temperature. 1 H NMR (400 MHz, C 6 D 6 ) d  ,8.07;N,7.15;Found: C,75.29;H,8.17;N,6.88.
After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.6 mg, 80.9 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 11 (35%). Figure S41. The 1 H NMR spectrum of the crude product for the synthesis of 11

Synthesis of 12
In a glovebox, a toluene solution (3 mL) of Xyl-NC (105 mg, 798 µmol) was added to a toluene solution (3 mL) of 1 (300 mg, 798 µmol) and pyrimidine (320 µL, 3.99 mmol) in a 30 mL vial at room temperature. During the reaction mixture was stirred at room temperature for 5 min, the color of the resulting solution turned to be green. Volatiles were removed from the reaction mixture under reduced pressure. The residue was
After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.3 mg, 79.1 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 12 (66%).   ,8.07;N,7.15;Found: C,75.29;H,8.17;N,6.88.
After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (600 µL) of 1,3,5trimethoxybenzene (13.8 mg, 82.1 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 13 (63%). Figure S43. The 1 H NMR spectrum of the crude product for the synthesis of 13
After stirring the reaction mixture for 10 min at room temperature, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3, 5-trimethoxybenzene (13.2 mg, 78.5 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature.
An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectra was recorded to estimate the NMR yield of 5e (54%). Figure S44. The 1 H NMR spectrum of the crude product for the synthesis of 5e

Estimation of NMR yield for the formation of 9e from 1
In a glovebox, a toluene solution (216 µL) of Xyl-NC (10.3 mg, 78.9 µmol) was added to a toluene solution (300 µL) of 6 (50.2 mg, 78.9 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 2 days at 60 °C, volatiles were removed from the reaction mixture under reduced pressure. A benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.6 mg, 80.9 µmol) was added to the residue and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 9e (68%). Estimation of NMR yield for the reaction of 1 with 2 eq. Xyl-NC and quinoline In a glovebox, a benzene-d 6 solution (300 µL) of Xyl-NC (21.0 mg, 160 µmol) was added to a benzene-d 6 solution (300 µL) of 1 (30.0 mg, 79.8 µmol) and quinoline (47.3 µL, 399 µmol) in a 15 mL vial at room temperature. After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (600 µL) of 1,3,5-trimethoxybenzene (13.5 mg, 80.3 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 3 (50%) and 5e (21%). It should be noted that 9e did not form at all in this reaction. Figure S46. The 1 H NMR spectrum of the crude product for the reaction of 1 with 2 eq. Xyl-NC and quinoline

Synthesis of 4f
In a glovebox, a toluene solution (1.
After stirring the reaction mixture for 10 min at room temperature, a benzene-d 6 solution (600 µL) of 1,3, 5trimethoxybenzene (13.4 mg, 79.8 µmol) was added to the crude product and the resulting mixture was stirred for 5 min at room temperature. An aliquot (600 µL) of the resulting solution was pipetted to a screw-capped NMR tube. After bringing the NMR tube out from the glovebox, 1 H NMR spectrum was recorded to estimate the NMR yield of 4f (50%). Figure S47. The 1 H NMR spectrum of the crude product for the synthesis of 4f

Synthesis of 14 by hydrolysis of 5
To a THF solution (5 mL) of 5 (150 mg, 0.256 mmol) in a 20 mL J.young tube, water (0.500 mL) was added at room temperature. The reaction mixture was stirred at 50 °C for 12 h (the color of the resulting solution turned to be red). The solvent was removed in vacuo to yield a brown oil, which was further subjected to flush chromatography on silica gel with a mixed eluent (AcOEt : hexane = 2 : 1). The first band (Rf = 0.86) was collected and solvent was removed by evaporation to afford