Synthesis of Pyrazolone Derivatives. XXXVIII. [1, 5] Sigmatropic Rearrangement during the Cycloaddition of (1R, 4S)-3-Diazobornane-2-one to Activated Acetylenes

Abstract

(1R, 4S)-3-Diazobornane-2-one was reacted with dimethyl acetylenedicarboxylate and methyl propiolate to give (4S, 7R)-4, 7-methano-8H-pyrazolo [1, 5-a] azepines (3a, b) (5R, 8S)-5, 8-methano-1H, 4H-cycloheptapyrazole (5) via spiropyrazole intermeadiate (6). The reaction from 6 to 3a, b and 5 is interpreted as a [1, 5] sigmatropic acyl rearrangement. Compound 3a was converted to (8R, 11S)-8, 11-methano-7H-benzo [3, 4] pyrazolo [1, 5-a]-azepine (12) and (8R, 11S)-8, 11-methano-7H-pyridazino [4', 5' : 4, 3] pyrazolo [1, 5-a] azepine (16). Treatment of 3a, b with sodium methoxide in methanol resulted in cleavage of amido linkage to yield (1R, 3S)-(pyrazol-5-yl) cyclopentanes (17a, b).