ENANTIOSELECTIVE PHOTOREACTIONS OF CYCLOOCTA-2,4,6-TRIEN-1-ONE AND CYCLOOCTA-2,4-DIEN-1-ONE IN THEIR INCLUSION COMPLEXES WITH (R,R)-(-)-1,6-BIS(O-CHLOROPHENYL)-1,6-DIPHENYLHEXA-2,4-DIYNE-1,6-DIOL - MECHANISTIC STUDY BASED ON X-RAY CRYSTAL-STRUCTURE ANALYSES

A host molecule, (R,R)-(-)-1,6-bis(o-chlorophenyl)-l,6-diphenylhexa-2,4-diyne-l,6-diol (1), includes two enantiomers (2a and 2b) of a guest molecule, cycloocta-2,4,6-trien-l-one (2), and gives the crystalline complex I (host:guest = 1:2). On the other hand, 1 includes one of the two enantiomers (4a and 4b) of cycloocta-2,4-dien-l-one (4) and produces the crystalline complex II (3:2). Irradiation of I and II in the solid state gives an optically active intramolecular photocyclization product, (-)-bicyclo[4.2.0]octa-4,7-dien-2-one (3), and an intermolecular pho-todimerization product, (-)-trans-anti-trans-tricyclo[8.6.0.02,9]hexadeca-7,ll-diene-3,16-dione (6a), respectively. Mechanisms of the enantioselective photoreactions of 2 in I and 4 in II were studied by X-ray crystal structural analyses. In both complexes I and II, one host links two guests through the O-H-O hydrogen bond. There are two enantiomers in complex I, in which one enantiomer, 2a, is enclosed loosely and another one, 2b, tightly. On the other hand, in complex II, there is a column composed only of host molecules, the column plays a role as chiral hydrophobic spacer, and one enantiomer, 4a, is included stereoselectively. Mechanisms of the enantioselective photoreactions of 2 in I and 4a in II are demonstrated. © 1990, American Chemical Society. All rights reserved.