A highly efficient, diastereo- and enantioselective route was developed to access a great variety of lignans. The asymmetric synthesis of the 2,3-disubstituted γ-butyrolactones 9a-c could be improved in the case of aldol reactions by employing 2.2 equivalents of LiCl as an additive to provide, after purification, highly diastereo- and enantioenriched starting materials for the synthesis of the furofuran lignans (-)-methyl piperitol, (-)-sesamin, and (-)-aschantin. Furthermore, the γ-butyrolactone 15 was converted into dibenzylbutyrolactone lignan (+)-yatein, the dibenzylbutandiol type (+)-dihydroclusin, the tetrahydrofuran type (+)-burseran, and the dibenzocyclooctadiene type (-)-isostegane.
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Enders et al. (2002) studied this question.