Title: Lewis Acid Catalysis in the Oxidative Cycloaddition of Thiophenes
Authors: Li, Yuanqiang 
Thiemann, Thies 
Sawada, Tsuyoshi 
Mataka, Shuntaro 
Tashiro, Masashi 
Issue Date: 14-Nov-1997
Publisher: American Chemical Society
Citation: The Journal of Organic Chemistry. 62:23 (1997) 7926-7936
Abstract: Thiophenes 1 were treated with m-chloroperbenzoic acid (m-CPBA) under BF3·Et2O catalysis to afford thiophene S-monoxides. These could be reacted in situ as intermediary species with a number of dienophiles to provide arenes (with alkynes as dienophiles) or 7-thiabicyclo[2.2.1]hept-2-ene 7-oxides (with alkenes as dienophiles). It was also possible to isolate thiophene S-monoxides in solution and to cycloadd them in a second step. In either way it could be shown that the use of BF3·Et2O enhances the yields of the oxidative cycloaddition of thiophenes considerably. Moreover a greater variety of dienophiles (29a, 29b, 29c) could be reacted with thiophenes than in the case of the noncatalyzed reaction. All cycloadditions catalyzed by BF3·Et2O give only a single diastereoisomer as cycloadduct. The reactions show a high π-facial selectivity, a fact that can be explained by the Cieplak-effect. Without added dienophiles, 2-methylthiophene (1e) gave a single dimer (36) of 2-methylthiophene S-monoxide, whereas 2,5-dimethylthiophene (1a) gave three dimers (32a−c). In the case of tetrasubstituted thiophenes, thiophene S-monoxides (e.g., 31b and 31c) could be isolated in substance.
URI: http://hdl.handle.net/10316/10321
ISSN: 0022-3263
Rights: openAccess
Appears in Collections:FFUC- Artigos em Revistas Internacionais

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