Unexpected reactions of alpha,beta-unsaturated esters with hydrazine hydrate

The reactions of hydrazine hydrate with methyl acrylate and ethyl acrylate do not result in the formation of 1,5-diazabicyclo[3.3.0]octane-2,6-dione 1 at reaction temperatures below 200 degreesC; 1,2-bis(alkoxycarbonylethyl)p yrazolidin-3-one 8, 1-(alkoxycarbonylethyl)pyrazolidin-3-one 6, and 2-(alko xycarbonylethyl)pyrazolidin-3-one 11 were isolated and identified. At 260-2 80 degreesC, however, 1 could be isolated in 20-28% yield; formation of 1 c ould also be observed by spectroscopic measurements when the reaction was c arried out above 200 degreesC. It is concluded that the major pathway invol ves initial Michael addition to give a 1,1-disubstituted hydrazine that can not yield 1 without undergoing unfavourable retro-Michael reactions. The ap parently similar reaction of hydrazine with excess diethyl glutaconate to g ive 4,8-bis(ethoxycarbonylmethyl)-1,5-diazabicyclo[3.3.0]octane-2,6-dione 2 takes a quite different course. Initial Michael addition gives a 1,2-disub stituted adduct for steric reasons. Although double cyclisation of this add uct to 2 appears straightforward, retro-Michael reaction of the monocyclise d adduct is very rapid and competes with the second cyclisation. The reacti on of ethyl methacrylate and hydrazine hydrate at 80 degreesC results in a complex reaction mixture, which is transformed into 4-methylpyrazolidin-3-o ne 13 at 390 degreesC under reduced pressure.