Asymmetric Diels–Alder cycloaddition of a di-P-stereogenic dienophile with cyclopentadiene

The Diels–Alder cycloaddition of the di-P-stereogenic dienophile (S_P,S_P)-1 leads to novel di-P-stereogenic norbornene derivatives and proceeds with moderate diastereoselectivity in the absence of a catalyst. In the presence of TiCl₄, however, the diastereoselectivity was raised to 9:1. The major diastereoisomer has been characterized crystallographically. The separation of the diastereomeric cycloadducts was possible by fractional crystallization in the presence of (?)-O,O-dibenzoyltartaric acid monohydrate.