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Paper | Regular issue | Vol 41, No. 9, 1995, pp.1967-1977
Published online, 1st January, 1970
DOI: 10.3987/COM-95-7091
■ A Study of 2-Propenethials Obtained by Flash Vacuum Pyrolysis of 2-Ethenyl-1,3-dithiolane 1,1-Dioxides

Li-Fan Liao, Pen-Wen Tseng, Chin-Hsing Chou, Wen-Chih Chou, and Jim-Min Fang

*Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, R.O.C.

Abstract

Synthesis of substituted 2-propenethials by the flash vaccum pyrolysis of appropriately substituted 2-ethenyl-1,3-dithiolane 1,1-dioxides has been investigated. Pyrolysis of 2-propenyl-1,3-dithiolane 1,1-dioxide (5a) gives thiophene, 2,5-dihydrothiophene, a [4+2] dimer (11) and a [4-+4] dimer (12) of 2-butenethial (4a). Pyrolysis of 2-(1-methylpropenyl)-1,3-dithiolane 1,1-dioxide (5b) gives 3-methylthiophene and a [4+4+4] trimer (14) of 2-methyl-2-butenethial (4b). Pyrolysis of 2-(2-phenylethenyl)-1,3-dithiolane 1,1-dioxide (5c) gives 2H-1-benzothiin (15) and a [4+2] dimer (16) of 3-phenyl-2-propenethial (4c). The dimer (11), 2-propenyl-4-methyl-4H-1,3-dithiin, can be considered as the meta-substituted cycloaddition product of 2-butenethial, whereas the dimer (16), 3-(2-phenylethenyl)-4-phenyl-3,4-dihydro-1,2-dithiin, can be considered as the ortho-substituted cycloaddition product of 2-phenyl-2-propenethial.