Pd-Catalyzed Strain-Releasing Dyotropic Rearrangement: Ring-Expanding Amidofluorination of Methylenecyclobutanes

Abstract

Under the Pd(II)/Pd(IV) catalytic cycle, the cyclization of pent-4-en-1-amine derivatives typically yields either pyrrolidines or piperidines depending on the N-protecting group. We report herein an unprecedented Pd(II)-catalyzed oxidative domino process that converts readily accessible N-protected 2-(2-amidoethyl)-1-methylenecyclobutane derivatives to 1-fluoro-2-azabicyclo[3.2.1]octanes. This transformation constructs three chemical bonds under mild conditions [Pd(hfacac)₂ (5.0 mol %), Selectfluor (2.0 equiv), MeCN, 60 °C, 10 min] through a domino sequence involving 5-exo-trig amidopalladation/Pd(II)–oxidation/chemoselective dyotropic rearrangement/C–F bond-forming reductive elimination. Notably, the cyclization mode remains independent of the N-protecting group under these conditions. Furthermore, diverse functional groups can be introduced at the bridgehead position of a bicyclic compound via an apparent anti-Bredt bridgehead iminium intermediate.