Enantioselective photochemical synthesis of a simple alkene via the solid state ionic chiral auxiliary approach

Irradiation of cis-bicyclo[4.3.0]non-8-ylacetophenone derivatives (1) in solution and the solid state yields cis-3a,4,5,6,7,7a-hexahydro-1H-indene (2) via a Norrish type II cleavage process. Asymmetric induction studies were conducted by providing the reactants with carboxylic acid substituents to which ionic chiral auxiliaries were attached through salt formation with optically pure amines. Irradiation of the salts (5 in total) in the crystalline state gave enantiomeric excesses of up to 44%. Single-crystal X-ray diffraction studies were performed on ketone la as well as salts 1d and 1g, and on this basis, the structure-reactivity relationships involved are discussed.