engleski

Chemistry of 1,3-Dioxepins. XII. 4,7-Dihydro-5-nitro-1,3-dioxepins in the Diels-Alder Reaction with 4-Methyloxazole

4,7-Dihydro-5-nitro-1,3-dioxepins 4 prepared by dehydrohalogenation of vic-chloronitro-dioxepanes 2 and/or dehydrohalogenation-demercuration of vic-chloromercurynitro-dioxepanes 3 represent reactive dienophiles in the Diels-Alder cycloaddition with 4-methyloxazole (5), giving pyridoxine (8) intermediates 1,5-dihydro-9-hydroxy-8-methyl-3H-[1,3]dioxepino[5,6-c]pyridines 6 in poor yields. The side products of this reaction were 4,7-dihydro-4-hydroxyimino-6-nitro-1,3-dioxepins 7, the structure of which was confirmed by parallel synthesis, i.e. by nitrosation of 4 with ethyl nitrite. The order of reactivity in the series of 5-substituted-4,7 -dihydro-1,3-dioxepins, calculated by AM1 semiempirical method, is predicted to be 5-nitro- > 5-unsubstituted- > 5-cyano- > 5-chloro-4,7-dihydro-1,3-dioxepin, and it is in agreement with experimental data.

Nitro-dioxepines; chloronitro-dioxepanes; dehydrohalogenation-demercuration; dienophles; Diels-Alder reaction; pyridoxine intermediates; hydroxyimino- nitro-dioxepins; semiempirical AM1 method

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