Synthesis and thermal transformations of pyrazolines obtained by 1,3-dipolar addition of diazocyclopropane to maleimides

Abstract

1 Pyrazolines, obtained by 1,3 dipolar cycloaddition of diazocyclopropane to N phenyl and N cyclohexylmaleimides, undergo complete dediazoniation at 175 °C for 10-16 h with the formation of spiro[3 azabicyclo[3.1.0]hexane 6,1´ cyclopropane] 2,4 diones 3 (80-89%) and isomeric 3 cyclopropyl 1H pyrrole 2,5 diones 4. On the example of 3 cyclopropyl 1 phenyl 1H pyrrole 2,5 dione, it was shown that compounds 4 are able again to enter into 1,3 dipolar cycloaddition with diazomethane or diazocyclopropane with the reaction in the case of diazocyclopropane being nonselective and leading to two regioisomeric pyrazolines in the ratio ~1.7 : 1, thermolysis of which, conversely, proceeds with high selectivity and exclusively affords a spiropentane derivative. An action of the aqueous methanol solution of sodium hydroxide on the spiropentanes fused with succinimide fragment and subsequent acidification of the salts obtained lead to stable cis amidoacids of spiropentane series.

One-pot catalyst-free synthesis of down- and upconversion fluorescent oligopyrazolines from diazoacetates and maleic anhydride

“…However, this reaction is rarely used in the synthesis of polymers, especially in the field of fluorescent polymers. To the best of our knowledge, only structure-analogues of MA, like maleimide 26 and furanone, 27 were exploited to react with diazocompounds leading to pyrazolines. Importantly, the resulting oligomer shows a 100-fold higher fluorescent emission compared with the monomer.…”

“…24,25 Although the copolymerization of diazocompounds with alkenes has been reported previously (vide supra), that with MA has never been researched thus far. To the best of our knowledge, only structure-analogues of MA, like maleimide 26 and furanone, 27 were exploited to react with diazocompounds leading to pyrazolines. As for MA, just the ring-expansion reaction was performed via the attack of carbene on the carbonyl carbon, along with the carbon-oxygen bond insertion, while the carbene was derived from oxadiazolines.…”