Studies on Pyrimidine Derivatives and Related Compounds. LXVIII. Reactions of Dialkyl Acylphosphonates with 1, 3-Disubstituted Benzimidazolium Halides

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The reaction of 1, 3-disubstituted benzimidazolium halides (1a-d, 16) with diethyl- and dimethyl acylphosphonates (2a-b, 12a-b) were investigated. 1 : 1 adducts (3a-b) were obtained from the reactions of 1a and 2a-b. From the reactions of 1a with 12a-b, 1b-d with 2a, and 1b-d with 12a-b were obtained betaines (13a-b, 3c-e, 13c-f), respectively. The adduct 3a was synthesized by an alternative method. Alkaline treatment of both 3a and 3b afforded 1, 3-dimethyl-2-(1-hydroxy)benzyl- and ethylbenzimidazolium iodides (8a-b) as major products. Alkaline treatment of betaines (13a-d, 3c-e) gave only corresponding 2-imidazolinones and/or ring-opened N-formates. Neither of the adducts gave corresponding quinoxaline derivatives. In the case of the reactions of 1, 3-dimethyl-5-nitrobenzimidazolium iodide (16) with 2a-b were obtained 1 : 1 adducts (17a-b) accompanied by ring-opened phosphates (18a-b). The reactions of 16 with 12a-b gave betaines (23a-b). Neither of 17a-b, 18a-b, or 23a-b gave corresponding quinoxaline derivatives. Treatment of 17a with dimethylsulfoxide afforded 1, 4-dimethyl-3-hydroxy-3-phenyl-7-nitro-1, 2, 3, 4-tetrahydro-2-quinoxalinone (25) in moderate yield. The mechanisms of these reactions are discussed briefly.