FORMATION OF 2 HETEROCYCLIC DIMERS FROM DIMETHYL DIAZOMALONATE AND BIS(METHOXYCARBONYL)CARBENE - PREPARATION AND TRAPPING OF METHOXY(METHOXYCARBONYL)KETENE WITH CYCLOPENTADIENE

Thermal decomposition of dimethyl diazomalonate (I) gives two dimers 9 and 10, in varying ratio and yield. depending on the reactant / solve nt. It is suggested that the kt tcne II, formed by Wolff rearrangement , reacts by two different pathways to produce the dimers: a mechanism which seems more reasonable than several alternatives. Independent pre paration of 11 in the presence of 1 did not produce either dimer bur w ith cyclopentadiene the 4-membered ring adduct y-7-(methoxycarbonyl)bi cyclo[3.2.0]hept-2-en-6-one (13) was produced. The structure of 13 was obtained by X-ray crystallography. Ab initio calculations (6-31G) in dicated that the observed product 13 was more thermodynamically stable than the isomeric adduct 16. (C) 1997 Elsevier Science Ltd.