Synthesis of Tetrasubstituted Alkenes through a Stannyllithiation

Key words

tetrasubstituted alkenes - stannyllithiation - diarylacetylenes

Significance

The authors disclose a stannyllithiation of diarylacetylenes to yield tetrasubstituted alkenes. Relatively few methods exist to access these synthons since regio- and stereoselectivity are often a problem. The utility of this strategy is showcased by a synthesis of two isomers of ­hydroxytamoxifen (5 and 6) and dibenzo[g,p]-chrysene (7).

Review: I. Beletskaya, C. Moberg Chem. Rev. 2006, 106, 2320-2354.

Comment

The regioselectivity of this transformation largely depends on the steric and electronic parameters of the aryl groups. In general, Me₃Sn adds to a carbon distal from ortho-substituted aryl groups and on the same carbon as electron-rich aromatic substituents. The alkenyllithium can be functionalized with a number of electrophiles, ranging from alkyl halides and carbonyl compounds to aryliodides through Negishi coupling after transmetalation to zinc. The vinylstannane can undergo cross-coupling reactions or be converted into a vinyliodide.