329358-20-5Relevant academic research and scientific papers
Regioselective 1,3-dipolar cycloadditions of (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines to acetylenic dipolarophiles
Turk, Cvetka,Svete, Jurij,Stanovnik, Branko,Golic, Ljubo,Golic-Grdadolnik, Simona,Golobic, Amalija,Selic, Lovro
, p. 146 - 156 (2001)
The 5,5-dimethylpyrazolidin-3-one (4), prepared from ethyl 3-methylbut-2-enoate (3) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a-i to give the corresponding (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a-i. The 1,3-dipolar cycloaddition reactions of azomethine imines 6a-h with dimethyl acetylenedicarboxylate (=dimethyl but-2-ynedioate; 7) afforded the corresponding dimethyl pyrazolo[1,2-a]pyrazoledicarboxylates 8a-h, while by cycloaddition of 6 with methyl propiolate (= methyl prop-2-ynoate: 9), regioisomeric methyl pyrazolo[1,2-a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a- i with methyl propiolate (9) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a-e derived from benzaldehydes 5a-e with a single substituent or without a substituent at the orthopositions in the aryl residue, led to mixtures of regioisomers 10a-e and 11a-e. Azomethine imines 6f-i derived from 2,6-disubstituted benzaldehydes 5f-i gave single regioisomers 10f-i.
