Palladium‐Catalyzed Cascade to Benzoxepins by Using Vinyl‐Substituted Donor–Acceptor Cyclopropanes. (26th May 2021) - Faltracco, Matteo
Abstract: A palladium‐catalyzed intermolecular cascade (4+3) cyclocondensation of salicylaldehydes and vinylcyclopropanes is reported. A key feature of the reaction is the use of a phosphonate group as an acceptor moiety on the cyclopropane, exploiting its propensity to undergo olefination with aldehydes. Subsequent O‐allylation enabled the formation of a range of substituted benzoxepinsWith a novel chiral ligand, the products were obtained in generally good yield and with reasonable enantioselectivity. Abstract : Enantiomerically enriched benzoxepins were synthesized from phosphonate‐functionalized vinylcyclopropanes and salicylaldehydes by palladium‐catalyzed ring opening followed by Horner–Wadsworth–Emmons olefination and subsequent O‐allylation (see scheme). In contrast to existing cycloaddition reactions of donor–acceptor cyclopropanes, the two bonds are each formed in a separate event, thus allowing greater flexibility in reaction design.