The synthesis of thiophenium and of oxazolium salts from diazoketones

4-Diazoacetylthianthren with perchloric acid in acetonitrile gave 2-oxo-1,2-dihydrothieno[3,2,1 -de]-thianthrenium perchlorate which gave the corresponding enol ether with diazomethane. This ether was compared with 3-methoxy-1-methylbenzo[b]thiophenium perchlorate, prepared from 3-methoxythiophen, and which was much more stable to solvolysis than the demethoxy-analogue. In contrast to the 4-diazoacetyithianthren, 7-diazoacetyl-2-methylbenzo[b]thiophen with acetonitrile and perchloric acid cyclised in an alternative mode to give a new synthesis of 2-methyl-4-substituted oxazolium perchlorates.