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

Abstract

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-6π 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.

Recent Advances in Oxa-6π Electrocyclization Reactivity for the Synthesis of Privileged Natural Product Scaffolds

“…During this methodological development, the authors noted that the second combination between 31b/32b was more sensitive to oxidation, which could be overcome by providing rigorous inert conditions in a glove box to generate the angular and highly substituted 2H-pyrans 34 in good yields. This tandem process was later evaluated by Mindt and successfully applied to the synthesis of benzoand naphtopyrans in a single step from readily available bromoquinone and vinyl stannane substrates [55].…”

“…During this methodological developmen authors noted that the second combination between 31b/32b was more sensitive to o tion, which could be overcome by providing rigorous inert conditions in a glove b generate the angular and highly substituted 2H-pyrans 34 in good yields. This tan process was later evaluated by Mindt and successfully applied to the synthesis of b and naphtopyrans in a single step from readily available bromoquinone and vinyl nane substrates [55]. In 2020, an oxidative dearomatization for the generation of ortho-quinone me with exquisite chemoselectivity has been reported to enable a series of tandem reac such as the oxa-6π electrocyclization [56].…”