Michael addition of N ‐isobutylidene‐ t ‐butylamine to dimethyl methoxymethylenemalonate and a new synthesis of some fused pyrazole derivatives from the adduct

N ‐Isobutylidenemethylamine reacted with dimethyl methoxymethylenemalonate to afford the N ‐alkylation product 3a exclusively. Exchanging the N ‐substituent of the Schiff's base from methyl to t ‐butyl altered the course of the reaction, allowing Michael addition to take place predominantly. The Michael adduct 4c on reaction with hydrazinoalkanols 6a,b, 6c,d and 6e gave tetrahydropyrazolo[5,1‐ b ]oxazoles 9a,b , tetrahydro‐pyrazolo[5,1‐ b ][1,3]oxazines 9c,d and hexahydropyrazolo[5,1‐ b ][1,3]oxazepine 9e , respectively.