CHEMISTRY OF 1,3-DIOXEPINS - XIII - (E) (Z) CONFIGURATIONAL ASSIGNMENT OF 4,7-DIHYDRO-4-HYDROXYIMINO-6-NITRO-1,3-DIOXEPINS/

The configuration of oximes 1a and 1b was investigated by chemical and spectroscopic methods. Under the Beckmann rearrangement conditions, u sing sulfonyl chlorides as reagents, the sulfonic esters 2a-c were obt ained. Under more drastic conditions, using PCl5, or P2O5, the only is olated product was 4-nitro-5H-furan-2-on (3). It was also formed as th e sole product by 'hydrolysis of oximes 1a-b, as well as sulfonic este r 2a. The structure of all compounds was determined by one- and two-di mensional homo- and hetero-nuclear H-1 and C-13 NMR correlated spectra : COSY, NOESY, HETCOR and HMBC. Gradient selected differential NOE mea surements confirmed that, in dimethylsulfoxide solution, oximes 1a and 1b exist in E-configuration, irrespective of the route of their forma tion.