科研之友
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摘要
Cross-coupling reactions typically rely on the use of transition metal catalysis. However, although achieving this process using metal-free organocatalysts is highly challenging, it could offer unique opportunities to discover novel bond-forming strategies in organic synthesis. Here we report a new amine catalysed direct stereoselective C-H alpha-arylation reaction of unmodified enals with bromoarenes. The power of this process, which involves an unprecedented iminium-Michael-alkylation-enamine-retro-Michael cascade sequence, has been demonstrated in the context of direct alpha-functionalization reactions of simple, unmodified enals with 4-bromophenols, 1-bromo-2-naphthol and 3-bromoindoles under mild reaction conditions. Notably, the process can be used for highly stereoselective syntheses of non-readily accessible E isomers, which normally require the use of transition metal-promoted cross-couplings and functionalized enals. The results of these studies significantly expand the scope of aminocatalysis.
