Ck. Ghosh et al., BENZOPYRANS - PART 39 - 2-AMINO-3-IMINOMETHYL-1-BENZOPYRAN-4-ONES DO NOT FUNCTION AS HETERODIENES, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 37(4), 1998, pp. 387-390
The hydrazone 3 (R-1=H and Me) in refluxing chloroform is converted by
dimethyl acetylenedicarboxylate (DMAD) to the aminonitrile 12 whereas
3 and 4 when refluxed in DMF with either DMAD or N-phenylmaleimide un
dergo self-condensation to the diazocine 12 and pyranopyrimidine 14, r
espectively instead of giving any [4+2]-cycloadduct.