Rhodium(ii)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones with 1-sulfonyl-1,2,3-triazole: synthesis of cyclopropa[cd]indole and benzofuran derivatives

Abstract

A rhodium(II)-catalyzed divergent intramolecular tandem cyclization of N- or O-tethered cyclohexa-2,5-dienones with 1-sulfonyl-1,2,3-triazole has been disclosed in this paper. When the connecting atom between the cyclohexa-2,5-dienone unit and the 1-sulfonyl-1,2,3-triazole moiety was a N-sulfonated group, a cyclopropanation of the olefinic unit in the cyclohexa-2,5-dienone moiety could take place, affording cyclopropa[cd]indole derivatives in moderate to good yields. This is the first example of the cyclopropanation of α-imino rhodium carbenes with electron-deficient intra-annular olefins. If the connecting linker was an oxygen atom, an oxy–Cope rearrangement could be triggered under similar reaction conditions, giving benzofuran derivatives. The reaction mechanisms have also been proposed along with a synthetic transformation.