Studies on the enantioselective catalysis of photochemically promoted transformations: "Sensitizing receptors" as chiral catalysts

A strategy for the enantioselective catalysis of photomediated reactions in solution is described, involving the use of chiral molecular receptors possessing appendant triplet-sensitizing moieties. Energy transfer is selectively directed to bound substrate as a consequence of the distance dependence of triplet-triplet energy transfer. This effect, which is equivalent to a binding-induced rate enhancement, enables substoichiometric chirality transfer from the receptor template to the substrate, as observed in the intramolecular enone-olefin photo[2 + 2]cycloaddition of a quinolone substrate.