Convergent synthesis of 2H-chromenes-a formal [3+3] cycloaddition by a one-pot, three-step cascade

[摘要] In cases in which the palladium-catalyzed coupling of a bromoquinone with a vinyl stannane affords a vinyl quinone that enolizes, the resulting ortho-quinone methide undergoes an oxa-6 pi electrocyclization. Enolization is promoted by the presence of a polar additive. The net conversion is a formal [3+3] cycloaddition that gives 2H-chromenes. Because the first two steps of the cascade are catalyzed, the overall conversion is an example of multicatalysis. Yields for the optimized, one-pot protocol are dramatically improved over the conventional stepwise process. (C) 2011 Elsevier Ltd. All rights reserved.

[发布日期] 2011-12-23

[关键词] Electrocyclization;Cascade;ortho-Quinone methide;Stille coupling;Formal [3+3] cycloaddition