text: In 1975, Mukaiyama reported that N-methyl-2-chloropyridinium iodide (also called 2-chloro-1-methylpyridinium iodide) allowed for a dehydration condensation between a carboxylic acid and an alcohol or similar functional groups to form an ester linkage. In the initial stage of the process, the carboxyl displaces the halogen atom on the reagent in the presence of a base. The resulting pyridyl ester is an activated electrophile and also serves as a good leaving group in a subsequent nucleophilic acyl substitution reaction with the alcohol reactant as nucleophile. Thus, the family of 2-halo-N-alkylpyridinium salts are named the Mukaiyama reagents. The reaction gives low yields if there are sterically large groups adjacent to the site of the reaction, such as tertiary carbons, but can be improved by using bromine as the halogen. In the years since its discovery, a number of different onium salts of aza-arenes have been used to catalyze a number of different dehydration reactions, including a macrolactonization. In 1994, Isamu Shiina developed his namesake macrolactonization in the Mukaiyama lab, making use of an aromatic carboxylic acid anhydride in the presence of a Lewis acid catalyst.