The synthesis of the first examples of Class II mesoionic xanthine acyclonucleosides is described. A series of mesoionic anhydro‐(8‐methoxyalkyl‐5‐hydroxy‐7‐oxothiazolo[3,2‐a]pyrimidinium hydroxides), Class II mesoionic analogs isoconjugate with xanthine, were prepared by the thermal condensation of methoxyalkyl‐2‐aminothiazoles with substituted bis(2,4,6‐trichlorophenyl)malonic esters. The memoxyalkyl‐2‐aminothiazoles were prepared via an aromatic nucleophilic substitution reaction between 2‐bromothiazole and the appropriate methoxyalkylamine in excess. The resulting 8‐methoxyalkyl‐substituted mesoionic xanthines were demethylated using iodotrimethylsilane in acetonitrile at room temperature to afford the corresponding mesoionic anhydro‐(8‐hydroxyalkyl‐5‐hydroxy‐7‐oxothiazolo[3,2‐a]pyrimidinium hydroxides) as the Class II mesoionic xanthine acyclonucleosides.

A Facile Preparation of Some Novel Class II Mesoionic Xanthine Acyclonucleosides.-The first examples of acyclonucleosides containing a six-membered mesoionic ring system (class II) are prepared with a view to the bacteriostatic and antifungal activities exhibited by related compounds. -(GIANDINOTO, S.; MBAGWU, G. O.; ROBINSON, T. A.; FERGUSON, C.; NUNEZ, J.; J.

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The reported substitutions are of the type PhsCeNCS --f Ph3CX and probably involve the ion Ph&+ as an intermediate. In strong acids, the isothiocyanate undergoes protonation and ionic dissociation, and gives the alcohol on addition of water; its dissociation is complete in concentrated sulphuric acid. Triphenylmethanol or its carboxylic esters are obtained from solutions in some carboxylic acids, but formic acid eventually causes complete reduction to triphenylmethane, whilst trifluoroacetic acid gives some triphenylmethylamine ; thiolcarboxylic acids give good yields of their triphenylmethyl esters. Observations on the reversibility of hydrolysis and alcoholysis of triphenylmethyl isothiocyanate are reported. The appropriate alkali-metal salts in organic solvents effect the substitutions, Ph&NCS + M X +Ph&X (X = OH, OMe, CN, N3, SCOR) ; the iodide, thus obtained, undergoes homolysis. The ready substitution reactions of triphenylmethyl isothiocyanate with solutions of silver nitrate, silver perchlorate, silver salts of carboxylic acids, and ferric chloride exemplify the assistance afforded by a transition-metal ion, but much more drastic conditions are needed for reaction with silver cyanide or mercuric cyanide.MOBILITY of the substituent group in organic thiocyanates is known chiefly with respect to the isomerisation reaction, for which there is evidence2 of ionisation as the intermediate step:

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