Pyridopyrimidines. Part VII. Reductive ring cleavage of pyrido[3,4-d]pyrimidin-4(3H)-ones with lithium aluminium hydride

Treatment of pyrido[3,4-d]pyrimidin-4(3H)-ones with lithium aluminium hydride has been shown to yield 3-amino-4-aminomethylpyridines. A 3-aryl substituent enhanced the rate of this cleavage at the 2,3-position, and 4-anilino-methyl-3-ethylamino-2,6-dimethylpyridine, for example, was isolated in excellent yield from a rapid reduction of 2,6,8-trimethyl-3-phenylpyrido[3,4-d]pyrimidin-4(3H)-one. Pyrido[3,4-d]pyrimidin-4(3H)-ones not bearing a 3-aryl substituent also underwent a reductive cleavage at the 2,3-position but much longer periods of time were required and 3,4-dihydro- and 1,2,3,4-tetrahydropyrido[3,4-d]pyrimidines were additionally obtained.