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.