NEIGHBORING GROUP EFFECTS ON RATES OF THERMOLYSIS OF 4-AZIDOTHIAZOLES

Rate measurements for thermolysis of 4-azidothiazoles in p-xylene solu tion have identified neighbouring group effects from nitro (19-fold ra te increase), phenyliminomethyl (16), formyl (4.5) and acetyl (2.2) su bstituents in the 5-position. These effects are very similar in magnit ude to those measured for 3-azidothiophenes, whereas in azidobenzenes the rate increases are much larger, 5-Substituents in 4-azidothiazole which are capable of conjugative donation (phenyl, ethyl propenoate) a lso increased the reaction rate. The reactions involving neighbouring group participation led to cyclized products from the 4-azidothiazoles though not all of these products were stable under the thermolysis co nditions. (C) 1997 Elsevier Science Ltd.