Syntheses and pyrolyses of benzofuran analogues of alpha-oxo-o-quinodimethane. A study on vinylcarbene-cyclopropene rearrangement.
Flash vacuum pyrolyses (FVP) of benzoic 3-methyl-2-benzofurancarboxylic anhydride (12) and benzoic 2-methyl-3-benzofurancarboxylic anhydride (13) at 550 degrees 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 alpha-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-alpha,alpha-d2 benzoate (28-d2).
Tseng
Pen-Wen
PW
Department of Chemistry and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, R.O.C.
Yeh
Su-Wen
SW
Chou
Chin-Hsing
CH