Hilbert-Johnson reaction halogenoses

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... 

The influence35 of solvents on the ratio of the a anomer to the / anomer is shown in Table III (see Section XII). It has been found that the anomer considerably predominated when the Hilbert-Johnson reaction of the bases 54 or 55 with the halogenoses 56,57, and 58 was performed in polar solvents, e.g., in acetonitrile or nitro-methane. On the other hand, in poorly polar solvents, e.g., in benzene or toluene, the value of the ratio a anomer// anomer is lower, but the anomer still predominates. 

The Hilbert-Johnson reaction of 5-halo-2,4-dimethoxypyrimidines with the halogenose (59) in acetonitrile or benzene as solvents afforded good yields of the corresponding l-(2,3,5-tri-0-benzoyl-j8-D-ribo-furanosyl)-4-methoxy-5-halo-2(l//)-pyrimidinonesfreeofaanomers.50... 

Recently, the use of mercuric bromide (in acetonitrile or benzene) in the Hilbert-Johnson reaction has been investigated.20,35,49 Thus, with 3,5-di-0-p-toluyl-2-deoxy-D-ribofuranosyl chloride, the reaction rate was higher in the presence of one or more molar equivalents of mercuric bromide, but the total yield of the anomeric mixture was considerably decreased because of the rapid decomposition of the deoxyhalogenose the amount of the j3 anomer in the anomeric mixture increased in this case. With stable halogenoses,49,60 the use of mercuric bromide leads to shorter reaction times (the total yield is not lowered to such an extent as with deoxyhalogenoses). 

In addition to the Hilbert-Johnson reaction, the so-called mercuri process,37 and, less frequently, the cyclization procedure of Shaw et a/.,53 64 have been used for the synthesis of nucleosides and their derivatives. l-Peracylglycosyl-4-alkoxy-2(l//)-pyrimidinones, the intermediates of the Hilbert-Johnson reaction, can be, in principle, prepared 56,56 also by the mercuri process, namely by reaction of 4-ethoxy-2(lZ/)-pyrimidinone chloromercuri salt with the corresponding halogenoses, but this method is of less importance because of the contamination of iV-l-glycosyl derivatives with the 0-2 isomers, namely, with 2-peracylglycosyloxy-4-alkoxypyrimidines. The advantageous features of the mercuri process in comparison with the Hilbert-Johnson reaction might be formulated as follows. 

The Anomeric Ratio op Products op the Hilbert-Johnson Reaction op Dimethoxyfyrimidines (54 and 55) with Halogenoses (56, 57, and 58) in Acetonitrile (Procedure A) and in Benzene (Procedure B)... 

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

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