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Paper | Special issue | Vol 52, No. 1, 2000, pp.365-382
Published online, 1st January, 1970
DOI: 10.3987/COM-99-S32
Synthesis, Isolation, and Dimerization and Trimerization of Monosubstituted Thiophene 1,1-Dioxides

Juzo Nakayama,* Hidehiro Nagasawa, Yoshiaki Sugihara, and Akihiko Ishii

*Department of Chemistry, Faculty of Science, Saitama University, Urawa, Saitama 338-8570, Japan

Abstract

Monosubstituted thiophenes were oxidized with dimethyldioxirane in acetone at -20 °C and then the solvent and volatile materials were removed below -40 °C. This allowed the isolation of kinetically labile 2-methyl-, 3-methyl-, 2-ethyl-, and 2-bromothiophene 1,1-dioxides (3a, 3b, 3c, and 3e, respectively) in practically pure form. These were characterized by 1H- and 13C-NMR, IR. UV/Vis, and MS spectroscopies. The half-lives of the parent thiophene 1,1-dioxide (1), 3b, 3a, and 3c were determined to be 14, 47, 68, and 76 mm, respectively, at 313 K (40 °C) in 0.32 M CDCl3 solutions. The 1,1-dioxide (3a) underwent a [4+2] cyclodimerization in which one molecule of 3a acted as a diene and the other as a dienophile to provide two isomeric products (4a and 5a). In addition, the trimeric product (16a) was formed owing to a further [4+2] cycloaddition of the major isomer (4a) with 3a which took place in the endo and head-to-head mode. Dimeric and trimeric products formation was also observed on decomposition of 3b and 3c, whereas 3e underwent only dimerization.