Asymmetric synthesis of 3-benzofuranones through 5-exo-trig cyclization of 4-nitroaryl olefins. Issue 31 (3rd August 2016)

• Record Type: Journal Article
• Authors: Verma, Nishant; Kumar, Sumit; Ahmed, Naseem
• Is Part Of: Tetrahedron letters. Volume 57:Issue 31(2016)
• Page Start: 3547
• Page End: 3550
• Publication Date: 2016-08-03
• Subjects: 3-Benzofuranones -- Organocatalyst -- Enantioselective -- 5-exo-trig cyclization -- 4-Nitroarylolefins; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tetlet.2016.06.118
• Languages: English
• ISSNs: 0040-4039

Abstract

Graphical abstract: Highlights: Organocatalyzed aldol condensation via intramolecular 5 -exo-trigonal cyclization. Conjugation effects of 4-nitroaryl moiety suitable for Baldwin's rule. Non-equilibrating intermediates (NEIs) regio- and enantioselective cyclization. ( S )-Pyrrolidinyl-tetrazole enantio-enriched gave 3-benzofuranones in 80–96.6% ee. Abstract: Organo-catalyzed aldol condensation of 2-hydroxyacetophenone and 4-nitrobenzaldehyde underwent regio- and enantioselective cyclization via intramolecular 5 -exo-trigonal cyclization to give 4-nitroaryl-3-benzofuranones. The product formation indicated that the proline bases (organocatalysts) suppressed the effect of carbonyl group by iminium ion formation and hence Michael addition is not possible. The conjugation effect moved toward 4-nitroaryl moiety suitable for 5 -exo-trig cyclization (Baldwin's rule). Thus, the non-equilibrating intermediates (NEIs) which gave in enantio-enriched 3-benzofuranones. A high enantioselectivity (80–96.6%) was obtained with ( S )-pyrrolidinyl-tetrazoleV under a metal-free condition.