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Paper | Special issue | Vol 47, No. 2, 1998, pp.933-950
Published online, 1st January, 1970
DOI: 10.3987/COM-97-S(N)103
[2+2] Versus [4+2] Cycloaddition Reactions of 1,3-Diaza-1,3-butadienes with Various Mono- and Disubstituted Ketenes and Supporting Mechanistic Considerations

Sucharita Mukherjee, Sujit N. Mazumdar, Arun K. Sharma, and Mohinder P. Mahajan*

*Department of Chemistry, North-Eastern Hill University, Shillong-793003, Meghalaya, India


Reactions of 1,3-diaza-1,3-butadienes with various mono- and disubstituted ketenes alongwith the associated interesting mechanistic features involved are reported. Reactions of 1,3-diazabutadienes with monosubstituted ketenes e.g. cyano-, p-nitrophenyl-, succinimido-, phthalimido- and phenoxyketenes gave [4+2] cycloadducts irrespective of the nature of azadiene and/or ketene substituents. However, diphenylketene underwent [2+2] cycloaddition reactions with 1,3-diazabutadienes (1a) and gave [4+2] adducts with 1b, having electron donating function at 2-position. Interestingly, the reactions of 4-(N-arylamino)-1,3-diaza-1,3-butadienes (19) with diphenylketene gave simple nucleophilic addition products (22), whereas, their reaction with dimethylketene, yielded [4+2] cycloadducts (23). The factors influencing [2+2] versus [4+2] and cyclic versus acyclic products are also discussed.