A process for preparing unsaturated esters useful as intermediates for HDAC inhibitors, by reacting an aldehyde or ketone having the following formula I: ##STR00001## wherein R.sub.1 is an aromatic group or a combined aliphatic and aromatic group; X is --O--, --S--, --COO--, --OOC--, --CONR.sub.7--, or --R.sub.7NCO--; L.sub.1 an aliphatic linking group, an aromatic linking group, or a combined aliphatic and aromatic linking group; R.sub.2 and R.sub.3 are each independently hydrogen, a hydroxy group, an alkoxy group, an amino group, a carboxyl group, an amide group, an ester group, a carbamate group, an aliphatic group, an aromatic group, a combined aliphatic and aromatic group, R.sub.2 and R.sub.3 together are .dbd.O, or one of R.sub.2 and R.sub.3 form a double bond with one of R.sub.4 and R.sub.5; R.sub.4 and R.sub.5 are each independently hydrogen, a hydroxy group, an alkoxy group, an amino group, a carboxy group, an amide group, an ester group, a carbamate group, an aliphatic group, an aromatic group, a combined aliphatic and aromatic group, or one of R.sub.4 and R.sub.5 form a double bond with one of R.sub.2 and R.sub.3; R.sub.6 is hydrogen, an aliphatic group, an aromatic group, or a combined aliphatic and aromatic group; R.sub.7 is hydrogen, an aliphatic group, an aromatic group, or a combined aliphatic and aromatic group; m is 0 or 1; n is 0 or 1; and p is 0 or 1; with an ester having the following formula II: ##STR00002## wherein R.sub.8 is an aliphatic group, an aromatic group, or a combined aliphatic and aromatic group; R.sub.9 and R.sub.10 each independently hydrogen, an aliphatic group, an aromatic group, a combined aliphatic and aromatic group, or one of R.sub.9 and R.sub.10 form a double bond with L.sub.2; R.sub.11 and R.sub.12 are each an aliphatic group, an aromatic group, or a combined aliphatic and aromatic group; L.sub.2 is an aliphatic linking group, an aromatic linking group, or a combined aliphatic and aromatic linking group; A is P or As; and p is 0 or 1.