Chemistry of 1 , 3 - Dioxepins . 111 . Dehydrohalogenation of 5 , 6 - Dihalogen - 1 , 3 - Dioxepanes with Strong Bases
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چکیده
Dehydrohalogenation of 5,6-dihalogen-1,3-dioxepanes II with KOH/MeOH or NaOCH3/MeOH under controlled reaction conditions gave mainly 5-halogen-4,7-dihydro-1,3-dioxepines III. Further substitution of vinylic-bromine in III whit KO-t-Bu/tert-BuOH or KOH/MeOH led to corresponding 5-substituted-4,7-dihydro-1 ,3-dioxepines some of which underwent spontaneous isomerization to 6,7-dihydro-1,3-dioxepines. Substitution of vinylic-bromine appeared to follow an elimination-addition mechanism with initial formation of an intermediate with a triple bond.
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