Single-crystal-to-single-crystal enantioselective [2+2] photodimerization of coumarin, thiocoumarin and cyclohex-2-enone in the inclusion complexes with chiral host compounds

Single-crystal-to-single-crystal enantioselective [2+2] photodimerization reactions of coumarin (la), thiocoumarin (Ib) and cyclohex-2-enone (2) were found to proceed efficiently in inclusion complexes with (R,R)-(-)-trans-bis(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxacyclopentane (3a), (R,R)-(-)-trans-2,3-bis(hydroxydiphenylmethyl)- 1,4-dioxaspiro[4.4]nonane (3b), and (-)-1,4-bis[3-(o-chlorophenyl)-3-hydroxy-3-phenylprop-1-ynyl]benzene (4), respectively. Through these reactions, (-)-anti-head-to-head dimer 6a, (+)-anti-head-to-head dimer 6b and (-)-syn-trans dimer 10 were obtained in 100, 100 and 48% ee, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.