Az—a colourful azulene-derived protecting group

Azulen-1-yl-dicarbonyl (Az) is a novel, coloured, protecting group used to mask primary and secondary alcohols. In particular, the use of Az in the construction of carbohydrates, where a number of orthogonal protecting groups are typically required, is of merit. Introduction and removal of the Az-group is performed easily and in near quantitative yields in the presence of other commonly used protecting groups, and the Az-group is compatible with glycosylation reactions using trichloroacetimidate donors. The deep-red colour of the Az-group greatly facilitates the purification of carbohydrate building blocks and the monitoring of coupling reactions. Of particular note is that the Az-group can be selectively introduced on diol systems and removed in the presence of esters, such as acetates.