Synthesis of Trisubstituted Alkenylstannanes through Copper-Catalyzed Three-Component Coupling of Alkylboranes, Alkynoates, and Tributyltin Methoxide

摘要

Alkenylstannanes are useful synthetic intermediates in organic synthesis because of their applicability in various transformations (e.g., Kosugi-Migita-Stille cross-coupling). In particular, trisubstituted alkenylstannanes should be useful for the synthesis of various tetrasubstituted alkenes that are found in many important pharmaceuticals and bioactive natural products. Among the routes to trisubstituted alkenylstannanes, transition-metal-catalyzed stereoselective carbostannylation of internal alkynes with organostannanes is the most straightforward and attractive (Scheme 1a). This catalytic method allows the simultaneous formation of C—C and C—Sn bonds. Shirakawa, Hiyama, and co-workers developed the palladium- or nickel-catalyzed carbostannylation of internal alkynes with allyl-, acyl-, and alkynylstannanes. These methods are useful for the preparation of trisubstituted alkenylstannanes, but require tedious preparation of the organostannane reagents. Additionally, sp~3-alkylstannanes have not been used for the introduction of alkyl groups. Furthermore, the regioselectivity is not always reliable, especially as the regiocontrol is generally difficult even with alkynes that are desymmetrized by electronic effects.