AN ABSOLUTE ASYMMETRIC-SYNTHESIS OF THE [2-TO-SINGLE CRYSTAL TRANSFORMATION BY CHARGE-TRANSFER EXCITATION OF SOLID-STATE MOLECULAR-COMPLEXES COMPOSED OF ARYLOLEFINS AND BIS[1,2,5]THIADIAZOLOTETRACYANOQUINODIMETHANE(2] CYCLOADDUCT VIA SINGLE CRYSTAL)

The title electron acceptor, 1,2,5]thiadiazolotetracyanoquinodimethane (BTDA,1), formed weak electron-donor-acceptor (EDA) complexes with ary lolefins such as styrene (ST) and divinylbenzenes (DVs). Upon charge-t ransfer (CT) excitation of these complexes in MeCN, the [2 + 2]-type c ycloadducts(2) were formed via a single electron transfer. Similar cyc loaddition reactions were efficiently induced when the solid-state mol ecular complexes of 1 and arylolefins were irradiated. In contrast to the close similarities in solution photochemistry, the solid state rea ctivities of three isomeric divinylbenzenes (oDV, mDV, pDV) were quite dissimilar because of the different molecular overlaps of 1 and DVs i n the crystal. The apparent reactivity of the oDV.1 crystal was much h igher than that in solution as in the case of the ST.1 crystal, and ad duct 2o was formed via the single crystal-to-single crystal transforma tion. Because of the asymmetric crystal structure in oDV 1, the optica lly pure product with 95% ee was obtained from the achiral components without any external chiral source. On the other hand, the incomplete conversion of the mDV.1 crystal to 2m is due to the crystal-to-amorpho us transformation, and the 1:2 adduct 6 was formed on irradiation of t he pDV.1 crystal which could not be obtained on excitation of the EDA complex in MeCN.