2,3-Diphenyl-, 2-methyl-3-phenyl-, and 2-methyl-3-(4-methylphenyl)cyclopropenone oxime hydrochlorides (3) were prepared in good yields from the corresponding cyclopropenones and hydroxylamine hydrochloride in methanol. The salts 3 reacted with alkyl and aryl isocyanates in the presence of triethylamine to afford 1:2 addition products 4,6-diazaspiro[2.3]hexenones in moderate yields. In contrast, acetone