The development of enantioselective reactions in organic photochemistry lags behind the progress achieved in conventional organic chemistry. Our approach to conduct enantioselective photochemical reactions in solution is based on the stoichiometric use of a chiral complexing agent (host), which transfers its chiral information to a corresponding substrate bound by noncovalent interactions.

Suitable substrates for enantioselective [2+2]-photocycloadditions in our host-substrate complexes have to offer a lactam binding site to reach an ideal association to host 1 (Figure 1) through hydrogen bonding. The sterically demanding tetrahydronaphthalene backbone of 1 shields one of the enantiotopic faces of a bound substrate. Facial stereocontrol increases with lower temperatures because the equilibrium is thus in favour of the host-substrate complex.

Figure 1: Principle of Face Differentiation.

Scheme 1: Current Results.