Orthoformic acid derivatives purines

A 2- or 6-hydroxy-substituted purine can be prepared from the corresponding 4,5-diamino-pyrimidinol by cyclization with an acid, ester, ortho ester, or amide. If the ring closure is performed with reagents such as urea, alkyl chloroformates, urethanes, phosgene, and alkyl isocyanates, the 8-hydroxypurines are formed. Various xanthine and uric acid derivatives have been prepared by the condensation of 5,6-diaminopyrimidine-2,4-diols with formic acid. Purin-2-ol (1) was prepared by this route from 4,5-diaminopyrimidin-2-ol and ethyl orthoformate. ... 

Some heterocycles can be linked to supports as tetrahydropyranyl derivatives. Attachment of indoles, purines, or tetrazoles (Table 3.29) has been achieved by treatment of a support-bound dihydropyran with the heterocycle in the presence of catalytic amounts of pyridinium tosylate [487], camphorsulfonic acid [539], or TFA [540] in DCE at 60-80 °C for 16-24 h. Indole-derived orthoesters, such as that in Entry 7 (Table 3.29), can be prepared by heating the indole with triethyl orthoformate (160 °C, 24 h) followed by acid-catalyzed reaction of the resulting orthoester with a resin-bound diol [541,542], As illustrated by Entry 8 (Table 3.29), indoles can also be linked to the Wang resin or related supports as carbamates. Cleavage by TFA is, how-... 

Cyclopropylamines react with aldehydes to yield the corresponding imines in fair yield.Cyclopropane-1,2-diamine reacted with two equivalents of benzaldehyde to give corresponding diimine 1 in 58% yield. Imine formation is also involved as the key step in multistep reactions leading to a variety of complex compounds. For example, 4-[2,2-bis(benzyloxymethyl)cyclopropylamino]-6-chloro-5-formamidopyrimidine (2) reacted with triethyl orthoformate in the presence of hydrochloric acid to give purine derivative 3 in 58% yield. An analogous reaction took place when 1-azido-l-vinylcyclopropane was treated successively with triphenylphosphane and benzaldehyde to give iV-benzylidene-l-vinyl-cyclopropylamine in almost quantitative yield. 

C]purines such as [ " CJgriseolic acid diester 135 in about 29% yield and, in 59% yield the [ CJimidazodiazepinone derivative 136. an intermediate in the synthesis of [ C]-pentostatin. Lastly, one example has been reported demonstrating that this type of reaction may be extended to other, appropriately 1,2-, 1,3- or 1,4-functionalized substrates thus, condensation of triethyl orthoformate with a highly substituted aryl hydrazide furnished 2-aryl substituted [5- C] 1,3,4-oxadiazole 137 in a low, but useful radiochemical yield of 10% l... 

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See also in sourсe #XX -- [ , ]

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