Syntheses and Pyrolyses of Benzofuran Analogues of α-Oxo-o-quinodimethane. A Study on Vinylcarbene−Cyclopropene Rearrangement

• Published in: Journal of organic chemistry 2008-05, Vol.73 (9), p.3481-3485
• Main Authors: Tseng, Pen-Wen, Yeh, Su-Wen, Chou, Chin-Hsing
• Format: Article
• Language: English
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Kinetics and mechanisms; Organic chemistry; Preparations and properties; Reactivity and mechanisms
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo702704e

Flash vacuum pyrolyses (FVP) of benzoic 3-methyl-2-benzofurancarboxylic anhydride (12) and benzoic 2-methyl-3-benzofurancarboxylic anhydride (13) at 550 °C and ca. 10−2 torr both give methylenebenzocyclobutenone (21) as the major product and indenone (22) as the minor one. A mechanism involving generation of α-oxo-o-quinodimethane 11 as the primary pyrolysis product from FVP of 13, followed by elimination of a CO molecule to give carbene 24, which undergoes a vinylcarbene−cyclopropene rearrangement and a ring contraction of the resulting carbene 23, is proposed to account for the observed results. The proposed mechanism is further supported by a deuterium-labeling study on FVP of (2-benzofuryl)methyl-α,α-d 2 benzoate (28-d 2).