A STUDY OF PERISELECTIVITY IN THE THERMAL CYCLISATION REACTIONS OF DIENE-CONJUGATED DIAZO COMPOUNDS: 1,7-CYCLISATION AS A ROUTE TO 3H-1,2-DIAZEPINES AND 1,5-CYCLISATION LEADING TO NEW REARRANGEMENT REACTIONS OF 3H-PYRAZOLES

Article abstract of DOI:10.1016/S0040-4020(01)82434-0

A range of diene-conjugated diazo compounds has been generated by the thermal decomposition of the sodium salts of the tosylhydrazones of 1-acyl-1,3-dienes. Those of type (21) with a cis relationship of the diazo group and the γ,δ-double bond and having a cis hydrogen atom at the dien terminus cyclised only by 1,7 ring closure to give 3H-1,2-diazepines (23).This mode of cyclisation was inhibited by the presence of cis methyl or phenyl groups at the diene terminus eg in (45). Compounds of this type cyclised by the alternative 1,5- ring closure to give 3-alkenyl-3H-pyrazoles eg (46) as primary products. These observations are explained on the basis of a helical transition state (54) for the 8? electron 1,7-electrocyclisation reaction. Diene-conjugated diazo compounds with a trans γ,δ double bond eg (32) also cyclised predominantly by 1,5-electrocyclisation to give 3-alkenyl-3H-pyrazoles eg (33). In most cases the 3H-pyrazoles rearranged under the reaction conditions via alkenyl group and hydrogen migrations to give 1H-pyrazoles eg (34) and (37).