Two approaches to the synthesis of boron-substituted pyrimidines and borazaroquinazolines (1) have been explored First, (dibutoxyboryl)ethene and bromomalononitrile were converted to l,l-dicyano-3-bromo-3-(dibutoxyboryl)propane (2), which was reduced with triphenyltin hydride to l,l-dicyano-3-(dibutoxyboryl)propane (3), which condensed with thiourea to yield 2-mercapto-4,6-diamino-5-(2-dihydroxyborylethyl)pyrimidine (4a). However, conversion of 4a to a borazaroquinazoline was not attempted because the development of boron-substituted carbanion chemistry promised a more direct and efficient approach. This second method involved condensation of 4,6-dichloro-5-formylpyrimidine (5) with the carbanion from tetrakis(trimethylenedioxyboryl)methane to form 4,6-dichloro-5-[2,2-bis(trimethylenedioxyboryl)vinyl]pyrimidine (6a), which on treatment with ammonia at 25 °C yielded 4-chloro-6-trimethylenedioxyboryl-7-hydroxy-7,8-dihydro-7,8-borazaroquinazoline (7a), which reacted with ammonia at 75 °C to form the 4-amino derivative 8. Improved yields were obtained in a similar sequence starting from tetrakis(ethylenedioxyboryl)methane. Characterization of the amino-substituted borazaroquinazolines was aided by 13 *C NMR correlations.Substitution of a boron atom for a carbon in a biochemically significant molecule might lead to antimetabolite ac-

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