Oxepins and Dioxepins

Carboxymethyl-S-ethoxyoxazole reacts with fumaronitrile to give 4,5-di-cyano-2-methyl-3-pyridinol. ° It reacts with 4,7-dihydro-l,3-dioxepine to give W-294, which is hydrolyzed with dilute hydrochloric acid to pyridoxine. The ethyl ester of Coarboxymethyl-5-ethoxyoxazole reacts with 1,3-dioxepine to form XII-294 and Xn-295, which can also be hydrolyzed to pyridoxine. S-Cyano-4-methyloxazole and 4,7-dihydro-l,3-oxepines have been used to... 

Having considered the expansion of a small ring into an oxepine, we should now look at the reverse, i.e. the contraction of a dioxepane into a furan derivative. Suzuki et have investigated the action of ruthenium hydride on olefins, and shown that they may be caused to migrate into conjugation with heteroatoms. Such a conversion can be used to mildly deprotect an alcohol previously masked as an allyl ether, but when applied to a suitable dihydro-l,3-dioxepine (407)... 

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