Halogenoborane mediated allene cyclooligomerization

Allene reacts with the strongly electrophilic halogenoboranes XB(C6F5)2 (X: Cl or Br) by forming a mixture of 1,3,5-trimethylenecyclohexane and the stoichiometric halogeno-borated tetramerization products.


Supporting Information
BrB(C6F5)2 (25.4 mg, 0.06 mmol) was dissolved in d8-toluene (0.5 mL) in a Young NMR tube. After evacuating the tube, the solution was exposed to allene gas for several minutes at room temperature. Then the resulting reaction mixture was characterized by NMR experiments after 4 hours at room temperature: a mixture with allene (ca. 91 mol%, 1 H), compound 1 (ca. 3 mol%, 1 H), and compound 3b (ca. 6 mol%, 1 H) as major components.
The NMR data of compound 1 in the reaction mixture are consistent with those reported in the literature [X. Tao, G. Kehr, C. G. Daniliuc andG. Erker, Angew. Chem. Int. Ed., 2017, 56, 1376. ] NMR data of compound 1: ClB(C6F5)2 (120 mg, 0.320 mmol) was dissolved in d8-toluene (2.0 mL) in a Schlenk tube. After evacuating the Schlenk tube, the solution was exposed to allene gas for several minutes at room temperature. Then the resulting reaction mixture was stirred for 48 hours at room temperature.    Single crystals suitable for the X-ray crystal structure analysis were obtained from diffusion of pentane vapor to a solution of the white powder in CH2Cl2 at room temperature.
X-ray crystal structure analysis of compound 4a (erk9164): A colorless plate-like specimen of C29H21BClF10N, approximate dimensions 0.020 mm x 0.060 mm x 0.100 mm, was used for the X-ray crystallographic analysis. The X-ray intensity data were measured. A total of 1882 frames were collected. The total exposure time was 34.10 hours. The frames were integrated with the Bruker SAINT software package using a wide-frame algorithm. The integration of the data using a triclinic with 8.155° < 2θ < 129.2°. Data were corrected for absorption effects using the multi-scan method (SADABS). The ratio of minimum to maximum apparent transmission was 0.823. The calculated minimum and maximum transmission coefficients (based on crystal size) are 0.8210 and 0.9600. The S15 structure was solved and refined using the Bruker SHELXTL Software Package, using the space group P1 , with Z = 2 for the formula unit, C29H21BClF10N. The final anisotropic full-matrix least-squares refinement on F 2 with 408 variables converged at R1 = 5.70%, for the observed data and wR2 = 16.70% for all data. The goodness-of-fit was 0.972. The largest peak in the final difference electron density synthesis was 0.267 e -/Å 3 and the largest hole was -0.255 e -/Å 3 with an RMS deviation of 0.059 e -/Å 3 . On the basis of the final model, the calculated density was 1.501 g/cm 3 and F(000), 628 e -. CCDC deposition number 1862533. BrB(C6F5)2 (127 mg, 0.300 mmol) was dissolved in d8-toluene (2.0 mL) in a Schlenk tube. After evacuating the tube, the solution was exposed to allene gas for several minutes at room temperature. Then the resulting reaction mixture was stirred for 48 hours at room temperature.

S19
Single crystals suitable for the X-ray crystal structure analysis were obtained from diffusion of pentane vapor to a solution of the white powder in CH2Cl2 at room temperature.
X-ray crystal structure analysis of compound 4b (erk9170): A colorless prism-like specimen of C29H21BBrF10N, approximate dimensions 0.158 mm x 0.170 mm x 0.303 mm, was used for the X-ray crystallographic analysis. The X-ray intensity data were measured. A total of 1382 frames were collected. The total exposure time was 16.14 hours. The frames were integrated with the Bruker SAINT software package using a wide-frame algorithm. The integration of the data using a triclinic ClB(C6F5)2 (165 mg, 0.434 mmol) was dissolved in d8-toluene (2.0 mL) in a Schlenk tube. After evacuating the Schlenk tube, the solution was exposed to allene gas for several minutes at room temperature. Then the resulting reaction mixture was stirred for 48 hours at room temperature.

S21
Subsequently, t Bu3P (175 mg, 0.868 mmol) was added. After stirring the reaction mixture for 24 hours at 60 o C, all volatiles were removed in vacuo and pentane (1 mL) was added to the residual oil.        Single crystals suitable for the X-ray crystal structure analysis were obtained from the diffusion of pentane vapor to a solution of the white powder in CH2Cl2 at room temperature.
Step 1: HB(C6F5)2 (20.8 mg, 0.06 mmol) was suspended in toluene-d8 (0.7 mL) and the atmosphere removed. After applying allene gas for 2 min, the mixture was stirred for 10 min at room temperature. The now clear solution was transferred to a NMR tube, which was then flame-sealed and heated to 60 °C for 24 h in a steel autoclave. Then the solution was filtered through a small plug of silica and ferrocene (9.8 mg, 0.05 mmol) was added as an internal standard. Step 2: Without further workup p-toluene sulfonic acid monohydrate (0.7 mg, 0.004 mmol; 5 mol%) was added to the solution from Step 1. After 1.5 h at room temperature, the 1 H NMR spectrum indicated complete conversion to mesitylene.
The cyclotrimer 14c (11.0 mg, 0.024 mmol) was dissolved in CD2Cl2 (0.7 mL) and p-toluene sulfonic acid monohydrate (0.2 mL, 0.001 mmol; 0.0055 M in CD2Cl2) was added. Then the solution was sealed in a NMR tube. After 22 h at room temperature, the reaction mixture was characterized by 1 H NMR experiment.
The cyclotrimer 14c (86.0 mg, 0.19 mmol) was dissolved in CH2Cl2 (10 mL) and p-toluene sulfonic acid monohydrate (2 mg, 0.01 mmol; 5 mol%) was added. Then the solution was stirred for 24 h at room temperature, during which it took on a brownish color. After removal of all volatiles in vacuo, the 1 H NMR spectrum of the crude product indicated a conversion of 75%. The crude product was dissolved in CH2Cl2 (10 mL) and another portion of p-toluene sulfonic acid monohydrate (2 mg, 0.01 mmol; 5 mol%) was added. After stirring for additional 24 h at room temperature and removal of all volatiles in vacuo, the 1 H NMR spectrum of the crude product indicated full conversion. Then the crude product was dissolved in pentane (10 mL) and passed through a small plug of silica. After rinsing of the silica plug with pentane (30 mL), all volatiles were removed in vacuo and compound 15c (72.0 mg, 0.15 mmol, 78%) was isolated as a yellowish oil.   Scheme S16.
The cyclotrimer 14e (8.8 mg, 0.024 mmol) was dissolved in CD2Cl2 (0.7 mL) and p-toluene sulfonic acid monohydrate (0.2 mL, 0.001 mmol; 0.0055 M in CD2Cl2) was added. Then the solution was sealed in a NMR tube, which was then placed in a steel autoclave and heated up to 80 o C for 5 hours. The reaction mixture was then characterized by 1 H NMR experiment.
The cyclotrimer (88.0 mg, 0.24 mmol) and p-toluene sulfonic acid monohydrate (4.6 mg, 0.024 mmol; 10 mol%) were mixed in CH2Cl2 (10 mL) in an ampule, which was subsequently placed in a steel autoclave. The autoclave was treated with argon (ca. 10 bar) and then heated up to 80 o C for 5 hours. After the autoclave was cooled down to room temperature, the argon was carefully released. A blue solution was obtained. All the volatile was removed by rotation evaporator and the residue was purified via column chromatography (silica gel, pentane) giving product 15e ( Figure S44. 1 H NMR (600 MHz, 299 K, CD2Cl2(*))spectra of (1) compound 14e, (2) the reaction mixture from Experiment 1, and (3) isolated compound 15e from Experiment 2. Figure S45. 1 H NMR (600 MHz, 299 K, CD2Cl2(*)) spectrum of isolated compound 15e from Experiment 2. Figure S46. 13 C{ 1 H} NMR (151 MHz, 299 K, CD2Cl2) spectrum of isolated compound 15e from Experiment 2. S44 X-ray crystal structure analysis of 15e (erk9371): A colorless plate-like specimen of C27H42  0.5 x CH2Cl2, approximate dimensions 0.050 mm x 0.101 mm x 0.224 mm, was used for the X-ray crystallographic analysis. The X-ray intensity data were measured. A total of 1217 frames were collected. The total exposure time was 21.26 hours. The frames were integrated with the Bruker SAINT software package using a wide-frame algorithm. The integration of the data using a triclinic unit cell yielded a total of 25656 reflections to a maximum θ angle of 66.84° (0.84 Å resolution), of which 8246 were independent (average redundancy 3.111, completeness = 98.3%, Rint = 5.52%, Rsig = 6.09%) and 5834 (70.75%) were greater than 2σ(F 2 ). The final cell constants of a = 10.8108(3) Å, b = 12.1099(3) Å, c = 19.1989(5) Å, α = 76.7030(10)°, β = 75.1760(10)°, γ = 87.9660(10)°, volume = 2363.95(11) Å 3 , are based upon the refinement of the XYZ-centroids of 9965 reflections above 20 σ(I) with 4.890° < 2θ < 133.7°. Data were corrected for absorption effects using the multi-scan method (SADABS). The ratio of minimum to maximum apparent transmission was 0.932. The calculated minimum and maximum transmission coefficients (based on crystal size) are 0.7330 and 0.9300. The structure was solved and refined using the Bruker SHELXTL Software Package, using the space group P-1, with Z = 4 for the formula unit, C27H42  0.5 x CH2Cl2. The final anisotropic fullmatrix least-squares refinement on F 2 with 639 variables converged at R1 = 6.90%, for the observed data and wR2 = 17.20% for all data. The goodness-of-fit was 1.030. The largest peak in the final difference electron density synthesis was 0.720 e -/Å 3 and the largest hole was -0.554 e -/Å 3 with an RMS deviation of 0.058 e -/Å 3 . On the basis of the final model, the calculated density was 1.149 g/cm 3 and F(000), 900 e -.

Figure S47
Crystal structure analysis of compound 15e [only one of two crystallographically independent molecules is shown (mol A); thermal ellipsoids: 30% probability].