摘要：

Methods for selectively protecting one of the degenerate nitrogen atoms of the cyclic urea derivatives 1,3-dihydro-2H-benzimidazol-2-one (6a), 1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one (11), 1,3-dihydro-2H-imidazo[4,5-b]quinolin-2-ones (20), 1,3-dihydro-2H-imidazo[4,5-c]pyridin-2-one (22), and 1,3-dihydro-4-phenyl-2H-imidazol-2-one (27) were developed. Heating these cyclic ureas with ethyl 2-pyridyl carbonate in the presence of a base in CH3CN at reflux or DMF at 100 degrees C cleanly provided the monoethoxycarbonyl derivatives 7a, 12, 21, 23, and 28, respectively. Alternatively, treatment of 6a with an excess of diethyl pyrocarbonate or di-tert-butyl dicarbonate afforded the bis-alkoxycarbonyl derivatives 8a and 8b, respectively, which underwent disproportionation to 7a and 7b upon heating with 1 mol equiv of 6a and K2CO3 in CH3CN at reflux. The regiochemistry of the introduction of alkoxycarbonyl groups to benzimidazol-2-one derivatives was not significantly influenced by an electron-withdrawing (CF3, 6b) or an electron-donating (OCH3, 6c) substituent at C-5 of the heterocyclic ring. However, the reaction was found to be sensitive to steric factors since a chlorine substituent ortho to one of the urea N atoms (6e) completely directed the alkoxycarbonyl moiety to the less sterically encumbered N atom, affording a single product (7f, 7g). Alkylation of 7a-g proceeded efficiently to provide products 10a-10ag after removal of the protecting group. Halogenation of monoprotected benzimidazol-2-one 7a occurred regiospecifically to give the monohalo derivatives 7h, 7i, and 7k, the identity of which were readily established from the characteristic chemical shift and spin coupling pattern in their 1H NMR spectra. A protecting group interchange strategy that took advantage of the distinctive chemical reactivities of the EtO(2)C and t-BuO(2)C protecting groups toward isopropylamine was developed that provided access to the isomerically substituted series of monohalo, mono-N-alkylated benzimidazol-2-ones 71 and 7m. The efficient derivatization of the unprotected N atom of these monoprotected cyclic urea derivatives was accomplished by treating with activated and unactivated halides in the. presence of K2CO3 or exposure to alcohols under Mitsunobu conditions. In several cases, mixtures of O- and N-alkylated products were produced which were readily separated by chromatography. Alkylation of 7h with activated halides, using K2CO3 in CH3CN at reflux, occurred without protecting group equilibration; however, a mixture of isomeric alkylated products was obtained when 7h was heated at 110 degrees C in DMF with cyclohexylmethyl bromide in the presence of K2CO3 as the base. Derivatization of 7h under Mitsunobu reaction conditions proceeded with retention of the topological substituent relationships. Subsequent removal of the alkoxycarbonyl moiety afforded monoalkylated cyclic urea derivatives.

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