figuration (Figure 8). Chemoselective esterification was obtained for phenolic carboxylic acids, accompa- nied by a slight amount of dialkylated products.
An efficient and selective esterification of carboxylic acids with chloroformates was reported using silica- supported hexaalkyl guanidinium salt (SiO2/PBGS- iCl) (Table 18, entry 11)160 (Figure 9). Aliphatic and