Formal [4+1] cycloaddition of camphor-derived sulfonium salts with aldimines: enantioselective synthesis of 2,3-dihydrobenzofurans

An asymmetric formal [4+1] cycloaddition of camphor-derived sulfonium salts with aldimines has been described. The reaction allows for the efficient synthesis of trans-2,3-disubstituted-2,3-dihydrobenzofurans in moderate to good yields with >95:5 dr and up to 98% ee under mild reaction conditions.