Scheme 2. Mechanism and CP light opportunities for asymmetric induction in the photochemical synthesis of dihydrohelicenes. 1a refers to the specific (chiral) reacting conformations of the cis-alkene whereas 1 is used to refer to the compound in all its conformations (see ESI, Fig. S2† for an expanded reaction scheme). Enthalpies cited come from DFT calculations (see ESI, Section S6.2†). In the absence of a stoichiometric oxidant, dihydrohelicene 3 should be the final product of the reaction, avoiding problems with competing reactions and product racemization.28,29 .
