I noted with interest the article by Sarpong et al about activation of carbonyl imidazolides (Org Lett, 2012, 14 (8), 1970) and was reminded of a couple of earlier reports that I’d read. Sarpong et al report that pyridinium hydrochloride can promote the formation of oxazolidinones, as shown below, as well as accelerating the esterification carboxylic acids with imidazole carbamates.
Previous reports to which I refer are from Gilday et al (OPRD, 2009, 13 (1), 106) where they reported the accelerating effect of imidazole hydrochloride when coupling anilines with carbonyl imidazolides and work reported in the text ‘Process Chemistry in the Pharmaceutical Industry’, ed T Braish and K Gadamasetti. This later example is again of interest to me as it brings further intriguing details to light in CDI-mediated coupling reactions and the excellent work and enhanced understanding that development chemists bring to the fore. In this case, it was the carbon dioxide was important and actually helped to promote the desired chemistry, with the intermediacy of the ‘anhydride’ species. The coupling was inferior when carbon dioxide was purged from the system and could be ‘kick-started’ by bubbling carbon dioxide through the mixture.