Synthesis of Tetrasubstituted Alkenes by Stereo- and Regioselective Stannyllithiation of Diarylacetylenes.

Addition of trimethylstannyllithium to a diarylacetylene takes place exclusively in an anti-fashion to produce a lithio vinylstannane intermediate. The regioselectivity of the addition is controlled by the steric and electronic property of the acetylene and reaches up to >99:1. The two newly formed C-metal bonds can be sequentially and stereospecifically transformed into two new C-C bonds as illustrated by stereoselective synthesis of 4-hydroxytamoxifen and its regioisomer. A tetraarylethene bearing different aryl groups can be synthesized similarly and cyclized to a substituted dibenzo[g,p]chrysene derivative via a palladium-catalyzed arylation reaction.