Dynamic induction of enantiomeric excess from a prochiral azobenzene dimer under circularly polarized light† †Electronic supplementary information (ESI) available: Synthesis, 1H NMR spectra, 13C NMR spectra, UV absorption plots, HPLC traces, and CD spectra of the compounds; crystallographic informat

We demonstrate the simultaneous induction of chirality and enantiomeric excess from a prochiral azobenzene dimer via a chiral regioisomer formed in situ upon CPL irradiation.


General experimental methods.
All solvents and chemicals were obtained from commercial sources and used without further purification, unless otherwise stated. 1 H and 13 C NMR spectra were recorded using a JEOL ECX 400 spectrometer, with tetramethylsilane as the internal standard.
Electrospray ionization (ESI + ) mass spectrometry was performed using an AccuTOF instrument (JMS-T100LC; JEOL). X-ray crystallographic data were acquired using a Bruker Smart Apex diffractometer. Absorption spectra were recorded using an Agilent 8453 spectrophotometer. CD spectra were recorded using a JASCO J-720 spectrophotometer; baseline correction and binomial smoothing were applied to the spectra. Photoisomerization studies were conducted using radiation from an LED source of 365 nm and a super-high-pressure mercury lamp (500 W, Ushio) after passage through 436-nm filters. High-performance liquid chromatography (HPLC) was performed using a Hitachi Elite La Chrome HPLC system and a Chiralpak IA column (Daicel Chemical Industries). Compositions of photostationary states were determined through HPLC analysis. A mixture of isopropanol and hexane (1:4) was used as the eluent in the HPLC experiments.

Synthesis
Compound 4: A mixture of 1-chloro-2,6-dintrobenzene (250 mg, 1.23 mmol), iodonaphthalene (320 mg, 1.26 mmol), and copper bronze (320 mg, 5.04 mmol) was heated at 120 °C for 12 h (until the spot for dintrochlorobenzene disappeared in TLC analysis). The product was extracted into CH 2 Cl 2 ; the combined extracts were washed with water and dried (MgSO 4 ). The solvent was evaporated under vacuum and the residue subjected to column chromatography (SiO 2 ; CH 2 Cl 2 /hexane, 2:3) to give a pale yellow solid (38% yield Compound 5: Compound 4 (100 mg, 0.34 mmol) was dissolved in a 2:1 mixture of EtOH and 1,4-dioxane (5 mL) and then the reaction flask was evacuated and backfilled with Ar three times. PtO 2 (10 mg, 0.4 mmol) was added under an Ar atmosphere and then the atmosphere was changed from Ar to H 2 . The reaction mixture was stirred at room temperature until TLC (mobile phase: 20% EtOAc/hexane) revealed a single spot, approximately overnight. The catalyst was removed by filtration over Celite; the solvent was evaporated to dryness under vacuum to yield a brownish solid (71 mg, 90% yield).           Figure S20. UV spectra of a solution of 3 (1.5  10 -3 M) in MeCN during thermal backisomerization after PSS 365 nm , at 30 °C in the dark for 7 days. Figure S21. Linear relationship between the logarithm of the change in absorbance (∆A = A I -A t , determined from the absorbance at 320 nm in the UV spectra, where A I is the initial absorbance before irradiation and A t is the absorbance at time t after PSS 366 nm ) and time for 3 after PSS 365 nm at 30 °C. S15

Estimation of the enantiomeric excess after CPL irradiation
The enantiomeric excess in the photoresolution process is estimated by the following calculation, The photochemical rate equations in a 1cm cell are [ZZ] and ε R-EZ , ε S-EZ , ε EE , ε ZZ are concentrations and molar extinction coefficients of R-EZ, S-EZ, EE, ZZ isomers, respectively, and φ EE→EZ , φ ZZ→EZ , φ EZ→EE , φ EZ→ZZ represents the quantum yields of photochemical isomerization from EE → EZ, ZZ → EZ, EZ → EE , EZ → ZZ, respectively.
At the photostationary state, Then, Equating 4 and 5, Since R-EZ and S-EZ enantiomers are chemically same, the interconversion quantum yields must be identical for symmetry reasons. Therefore equation 7 can be written as Kuhn anisotropy factor, g is defined as, g = Δε /ε (12) from the equations 11 and 12, equation 13 can be obtained,