Regioselective 1,3-Dipolar Cycloadditions of (1Z)-1-(Arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide Azomethine Imines to Acetylenic Dipolarophiles

✍ Scribed by Cvetka Turk; Jurij Svete; Branko Stanovnik; Ljubo Golič; Simona Golič-Grdadolnik; Amalija Golobič; Lovro Selič

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: German
• Weight: 137 KB
• Volume: 84
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/1522-2675(20010131)84:1<146::aid-hlca146>3.0.co;2-7

✦ Synopsis

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-2ynedioate; 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.