2.4- Dialkoxypyrimidines, reaction with

Peracylglycopyranosyl halides (a-acetobromoglucopyranose,1,3-5 3,4,6-tri-0-acetyl-2-acetamido-2-deoxy-D-glucopyranosyl chloride13) react with 2,4-dialkoxypyrimidines with the formation of C-l -C-2 -trans derivatives whereas the corresponding cis derivatives were encountered rarely (e.g., in the reaction with 2,3,4-tri-0-acetyl-/9-D-ribopyranosyl bromide12). 

Dialkoxypyrimidines, Hilbert-Johnson reaction of, 8, 115 Diazepines, chemistry of, 8, 21 Diazomethane, reactions with heterocyclic compounds, 2, 245 Diquinolylmethane, and its analogs, 7, 153... 

Pliml, J., Prystas, M., The Hilbert-Johnson Reaction of 2,4-Dialkoxypyrimidines with Halogenoses, 8, 115. 

Heterodienophiles, new, heterocyclic synthesis using, 55, 1 Heteropentalenes, 69, 271 Hilbert-Johnson reaction of 2,4-dialkoxypyrimidines with halogenoses, 8, 115... 

By use of the Hilbert-Johnson procedure,139,140 a synthesis186 of cytidine (II) was effected this involved condensation of crude tri-O-acetyl-D-ribo-furanosyl bromide with a 2,4-dialkoxypyrimidine, followed by treatment of the crude reaction mixture with alcoholic ammonia. Although the yields were low, this achievement marked the first synthesis of a naturally occurring nucleoside. 

The synthesis of cytidine9 by the Hilberb-Johnson procedure (which may be formulated as a reaction of 2,4-dialkoxypyrimidines with halogenoses) initiated further investigations in the field of the pyrimidine nucleoside synthesis. Thus, for example, the treatment of... 

Application of 2,4-bis(trimethylsilyloxy)pyrimidines23-25 instead of 2,4-dialkoxypyrimidines is mentioned in the section dealing with modified Hilbert-Johnson reactions (Section III). 

Under conditions of the Hilbert-Johnson reaction, the 2,4-dialkoxypyrimidines (29) can furnish the following by-products uracil,13 1-alkyluracil,3-7 1,3-dialkyluracil,19 4-alkoxy-2(lIZ)-pyri-midinone,7 and l-alkyl-4-alkoxy-2(lH)-pyrimidinone.7,20 Thus, for example, 5-chloro-, 5-bromo-, and 5-iodouracil were isolated32- 33 as by-products in the Hilbert-Johnson reaction (in acetonitrile at 20°) of the corresponding 5-halo-2,4-dimethoxypyrimidines and 3,5-di-O-p-toluyl-2-deoxy-D-ribofuranosyl chloride. The formation of 1,3-dimethyluracil and 1,3,5-trimethyluracil as by-products has been observed quite recently19 when the reaction of 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride with 2,4-dimethoxypyrimidine and 5-methyl-2,4-dimethoxypyrimidine, respectively, was performed in toluene at 70°. 

The reaction of a 2,4-dialkoxypyrimidine with a halogenose (or an alkyl halide) has been assumed by Hilbert30 to proceed via a quaternary salt as intermediate. Thus, the stable l-methyl-2-methoxy-4-... 

The reactivity (in acetonitrile as solvent) of various 2,4-dialkoxy-pyrimidines19 towards 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride (59) was found to decrease in the order 2,4-dibenzyloxy-, 2,4-bis(p-methoxybenzyloxy)-, 2,4-dimethoxy-, 2,4-diethoxy-, 2,4-bis(2,4-di-methoxybenzyloxy), 2,4-diisopropoxypyrimidine. In all these cases, the j8 anomer represented the sole reaction product. In view of this stereospecificity, the reaction of the halogenose (59) with the above 2,4-dialkoxypyrimidines represents a procedure of choice for preparation of uridine or cytidine and their derivatives. When the Hilbert-... 

Hilbert-Johnson Reaction of 2,4-Dialkoxypyrimidines with Hologenoses S ... 

Hilbert-Johnson reaction. Reaction of 2,4-dialkoxypyrimidines with halogenoses to yield pyrimidine nucleosides. 

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