Investigations on diazo compounds and azides- LXII.1 1 Part LXI: H. Heydt, P. Eisenbarth, K. Feith and M. Regitz, J. Heterocycl. Chem., 22, (1985), in press. Synthesis and reactions of a-diazo phosphonates with a conjugated 1,3-diene unit

Article abstract of DOI:10.1016/S0040-4020(01)96364-1

α-Diazo phosphonates with a conjugated 1,3-diene unit are synthesised by the Bamford-Stevens reaction (2 →4→3). They undergo [4+2]-cycloadditions with the dienophile 5 to form the tetrahydrotriazolopyridazines 8, which possess an unchanged diazo group. In contrast, dimethyl acetylenedicarboxylate (9) reacts exclusively with the diazo dipole of 3 to yield the 3H-pyrazoles 10, which rearrange to 11 by sigmatropic PO-shifts and hydrolyse to form 13. The diazo compound 3b isomerises to the pyrazole 16 when heated in benzene.