NEW SYNTHETIC ROUTES TO PYRROLO-[1,2-A]-IMIDAZOL-5-ONES AND PYRROLO-[1,2-C]-IMIDAZOL-5-ONES BY FLASH VACUUM PYROLYSIS

1-Substituted and 1,3-disubstituted pyrrolo[1,2-c]imidazol-5-ones 25-2 7 have been made in fair to excellent yield by flash vacuum pyrolysis (FVP) of the Meldrum's acid precursors 11-13, FVP of the appropriate p ropenoate precursor 23, 22 and 18-20 gives pyrrolo[1,2-c]imidazol-5-on e 2, pyrrolo[1,2-a]-imidazol-5-one 3 and their 6-methyl derivatives 28 -30 respectively in 32-90% yield, The mechanism of the propenoate pyro lyses involves rate determining E to Z-isomerisation of the alkene fol lowed by elimination of an alcohol and electrocyclisation to the fused ring products.