Syntheses of pyrimido[4,5-c]pyridazine derivatives. II. A novel reaction of .ALPHA.-diazo-.BETA.-oxo-5-(4-chloropyrimidine)propionate with triphenyl phosphine leading to 1,4-dihydro-4-oxopyrimido[4,5-c]pyridazine-3-carboxylate.

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A new and convenient synthetic method was presented for the derivatives of the pyrimido [4, 5-c] pyridazine. Reactions of α-diazo-β-oxo-5-(4-chloro-2-substituted pyrimidine) propionates (1a-c) with triphenyl phosphine afforded ethyl 1, 4-dihydro-4-oxo-7-substituted pyrimido [4, 5-c] pyridazine-3-carboxylates (3a-c) in good yields. α-Diazo-β-oxo-5-(4-methoxy-2-methylthiopyrimidine) propionate (5a), when treated with triphenyl phosphine in the same conditions, yielded {[1-ethoxycarbonyl-2-oxo-2-(4-methoxy-2-methylthio-5-pyrimidinyl) ethylidene] hydrazono} triphenyl phosphorane (6a) which was an intermediate for the 7-methylthio derivative (3a). The conversion of 6a into 3a was effected by treating with aqueous alcohol via ethyl α-hydrazono-β-oxo-5-(4-methoxy-2-methylthiopyrimidine) propionate (7a). The 2-phenyl derivative (5b) gave the 7-phenyl analog (3b). Reaction mechanisms for 1 leading to 3 were discussed.

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