Uracils reaction with nitrile oxides

In a recent paper, Kim and Ryu have demonstrated that the reaction of some stable nitrile oxides with uracil nucleosides cleanly gave products of 1,3 addition (Scheme 34). The 5-aroylpyrimidine nucleoside oximes 57-64 were prepared in moderate to good yield by the reaction of hydroximoyl chlorides 55a-e with the corresponding pyrimidine nucleosides 56a-d. 

Bicyclic A(0-Mti-homonucleoside analogues such as 591 were synthesized through 1,3-dipolar cycloaddition of an enantiopure 3-hydroxy-l-pyrroline A -oxide and protected allyl alcohol and subsequent introduction of thymine by a Mitsunobu reaction <2003T5231>. Furthermore, isoxazole, isoxazoline, and isoxazolidine analogues of (7-nucleo-sides such as 592-594 were synthesized by 1,3-dipolar cycloaddition of nitrile oxides and nitrones derived from uracil-5-carbaldehydes with suitable dipolarophiles <2003T4733, 2006T1494>. 

Nitrile oxides undergo dipolar [3 + 2] cycloadditions to carbon-carbon double bonds and triple bonds, for example, as in reactions 17-19 with an olefin a uracil derivative ... 

Furthermore, Bauerle and Emge prepared uracil-substimted end-capped terthiophene 2.188 and bithiophene 2.189 (Scheme 1.24) [283, 284]. Compound 2.188 was prepared by reaction of 5-bromopentyl-substituted terthiophene with orotic acid in 38% yield. Bithiophene derivative 2.189 was synthesized by conversion of 3-(5-bromopentyl)-2,2 -bithiophene to the nitrile and carboxylic acid followed by reaction with 6-(chloromethyl)uracil in 36% yield. Molecular recognition properties of 2.188 and 2.189 with complementary acetyl-9-octyladenine and 2,4-diacetamido-6-pentoxypyrimidine were smdied by cyclic voltammetry in CH2CI2 solutions. A positive shift of the oxidation potential (AE = 20-130 mV) was observed upon addition of complementary nucleobases to the electrolyte. 

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