Self assembly assisted preparation of a homochiral porphyrin

The multiple alkylation of porphyrin 3 by four equivalents of the homochiral ditosylthreitol 4 proceeded in high yields, and only one of the two possible isomers was formed. The crystal structure of the product 5 suggests that that this novel phenomenon is a consequence of conformational changes, induced by the first alkylation. The formation of the first bridge completely eliminates the possibility of obtaining one of the isomers, while at the same time it seems to assist in the formation of the other isomer in a self assembly fashion. (C) 1996 Elsevier Science Ltd