Wavelength Control of Diastereodifferentiating Paternó−Büchi Reaction of Chiral Cyanobenzoates with Diphenylethene through Direct versus Charge-Transfer Excitation

In the diastereodifferentiating Paterno-Buchi reaction, the excited CT complex was distinctly different in structure and reactivity from the conventional exciplex, and the inherent diastereofacial selectivity and its temperature dependence were opposite to each other in these two excitation modes. Thus, the combined use of wavelength and temperature not only reveals the mechanistic details but also provides a new convenient, powerful tool for critically controlling the stereochemical outcomes of asymmetric photoreactions.