Excess Of Carboxylic Acid Research Articles

Intramolekulare 1,3‐dipolare Cycloadditionen von Diarylnitriliminen aus 2,5‐Diaryltetrazolen

Intramolecular 1,3‐Dipolar Cycloadditions of Diaryl‐nitrile‐imines Generated from 2,5‐Diaryl‐tetrazolesAlkenyl‐substituted diaryl‐nitrile‐imines – generated by photolysis or thermolysis of alkenyl‐substituted 2,5‐diaryl‐tetrazoles ‐ undergo a regioselective intramolecular [2 + 3] cycloaddition to yield new heterocyclic compounds, e. g. fused 2‐pyrazolines. With alkinyl derivatives, the corresponding pyrazoles have been formed. UV evidence is given for the intermediate nitrile‐imine at − 190°. The latter can be trapped using an excess of carboxylic acid (UV evidence for a new intermediate at − 120°). In this case, the corresponding rearranged addition product N′‐acyl‐N′‐aryl‐benzohydrazide is isolated in good yield.

The use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in the selective N4-acylation of cytidine and its derivatives

Cytidine and its nucleoside derivatives reacted with an excess of carboxylic acid and of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) in dimethyl-formamide as solvent to form the corresponding N 4-acyl derivatives. In this way, the N 4-benzoyl, -acetyl, and tert.-butyloxycarbonyl- l-phenylalanyl derivatives of 2′- O-tetrahydropyranyl cytidine, 2′-deoxycytidine, and cytidine, respectively, were formed and isolated in yields of 75–90 %. No significant O-acylation was detected. Reaction of 2′,3′- O-isopropylidene cytidine with anisic acid and EEDQ led to appreciable O-acylation and the isolated yield of N 4-anisoyl-2′,3′- O-isopropylidene cytidine was only 40 %. None of the nucleosides of adenine and guanine tested under the same conditions gave appreciable amounts of their N-acetyl derivatives so the method is restricted to cytidine and its derivatives.