Selectivity in cycloadditions—X : Regiochemistry of cycloadditions of nitrile oxides to thiophene and benzothiophene 1,1-dioxides |
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Authors: | F Marinone Albini P Ceva A Mascherpa E Albini P Caramella |
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Institution: | Institute of Organic Chemistry, University of Pavia, Viale Taramelli 10, 27100 Pavia, and Department of Chemistry, University of Catania, Viale A. Doria 8, 95125 Catania Italy |
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Abstract: | Thiophene-1,1-dioxide undergoes regioselective cycloaddition to benzonitrile oxide. In the reaction with the less reactive mesitonitrile oxide the sulfur dioxide deriving from the dimerization of the dipolarophile causes a catalytic decomposition of the nitrile oxide, which competes with the cycloaddition. Benzothiophene-1,1-dioxide and the vinyl sulfone system of 2,3-dihydrothiophene-1,1-dioxide and nitrile oxides with lower regioselectivity. The directing effect of the sulfonyl group has been elucidated with the aid of CNDO/2 calculations. |
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