Enantioselective Trifunctionalization of Terminal Alkynes.

The stereoselective synthesis of alkenes has been one of the central objectives in organic chemistry. Significant advances in synthetic methodology have made mono- and disubstituted alkenes widely accessible from a variety of readily available precursors. However, increased steric hindrance in more highly substituted alkenes limits the effectiveness of these methods, and as a result, the efficient and selective synthesis of highly substituted alkenes remains a formidable challenge. Here, we demonstrate palladium-catalyzed trifunctionalization of terminal alkynes using organoboranes and allylic carbonates as coupling partners. This transformation provides tetrasubstituted alkenes with excellent regioselectivity and diastereoselectivity. Moreover, regiodivergent, diastereo- and enantioselective incorporation of the allylic fragment provides access to a wide range of complex 1,4-diene products. We present evidence that the palladium catalyst controls the selectivity of tetrasubstituted alkene formation and the selectivity of allylic substitution.