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Rate measurements for thermolysis of 4-azidothiazoles in p-xylene solution have identified neighbouring group effects from nitro (19-fold rate increase), phenyliminomethyl (16), formyl (4.5) and acetyl (2.2) substituents in the 5-position. These effects are very similar in magnitude 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) also 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 conditions. |
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