Regiospecific Reduction of the 2-Carbonyl Group of the 6-Hydroxypyrimido[2,1-f]purine-2,4,8(1H,3H,9H)-trione System by Selected Metal Hydrides. A Novel Reduction of a Fused Xanthine Nucleus
A series of substituted 6-hydroxypyrimido[2,1-f]purine-2,4,8(1H,3H,9H)-triones 1 have been reduced to the corresponding 2,3-dihydro-6-hydroxypyrimido[2,1-f]purine-4,8(1H,9H)-diones 2 by treatment with excess lithium borohydride in refluxing dioxane or sodium bis(2-methoxyethoxy)aluminum hydride in a refluxing dimethoxyethane-toluene mixture. The reduction occurs regiospecifically at the carbonyl group at the 2-position of the tricyclic nucleus, as demonstrated by spectroscopic and X-ray crystallographic data. The only side products observed are chromatographically immobile materials. Other reducing agents such as sodium borohydride, borane-tetrahydrofuran, or lithium aluminum hydride fail to effect this reduction. In order to achieve practical reaction rates with lithium borohydride, the solubilities of the substrates have been enhanced by means of silylation. MNDO calculations of the relative stabilities of postulated reaction intermediates suggest a possible explanation of the observed regiospecificity of the reduction. © 1988, American Chemical Society. All rights reserved.
Conn, DJ; Kaminski, JJ; Solomon, DM; McPhail, AT
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