Stereoselective Nazarov Cyclizations of Bridged Bicyclic Dienones
摘要:
Bridged bicyclic dienones underwent silyl-directed Nazarov cyclization with generally very high diastereoselectivity. In most cases, a strong preference for cyclization to the product with an exo-disposed cyclopentenone was seen. However, the presence of additional unsaturation in the three-carbon bridge of a bicyclo[3.2.1]octadiene system caused complete reversal in selectivity with exclusive formation of the endocyclopentenone. The observed selectivities are believed to result from a combination of steric and electronic effects.
Improved Yields with Added Copper(I) Salts in Carbonylative Stille Couplings of Sterically Hindered Vinylstannanes
摘要:
Stille coupling under standard carbonylative conditions proceeds in poor yield when using hindered alkenylstannane and enol triflate partners. The inclusion of 35 mol % CuI or CuBr significantly improves the efficiency of the coupling, providing a variety of complex 1,4-dien-3-ones in good to excellent yield.