TY - JOUR
T1 - Lewis Acid Catalysis in the Oxidative Cycloaddition of Thiophenes
AU - Li, Yuanqiang
AU - Thiemann, Thies
AU - Sawada, Tsuyoshi
AU - Mataka, Shuntaro
AU - Tashiro, Masashi
PY - 1997
Y1 - 1997
N2 - Thiophenes 1 were treated with m-chloroperbenzoic acid (m-CPBA) under BF3·Et2D 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 5-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. 1 Graduate School of Engineering Sciences, Kyushu University 2 Institute of Advanced Material Study, Kyushu University 3 Universidade de Coimbra.
AB - Thiophenes 1 were treated with m-chloroperbenzoic acid (m-CPBA) under BF3·Et2D 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 5-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. 1 Graduate School of Engineering Sciences, Kyushu University 2 Institute of Advanced Material Study, Kyushu University 3 Universidade de Coimbra.
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U2 - 10.1021/jo961985z
DO - 10.1021/jo961985z
M3 - Article
AN - SCOPUS:0000314020
SN - 0022-3263
VL - 62
SP - 7926
EP - 7936
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
IS - 23
ER -