ABSTRACT
Phosphate and especially sulfonate esters (e.g., tri ates, mesylates, and tosylates) are extensively used in organic chemistry, mainly under thermal conditions, with the R groups (in compounds 1 and 2 in Schemes 17.1 and 17.2) being the most important moiety. e phosphate or sulfonate esters act as suitable leaving groups having the exclusive role of activating the R groups for the synthesis of the target compound (R-Nu) and are thus eliminated at the end of the reaction (paths a and b). Actually, the capability of sulfonate esters as leaving groups in aliphatic nucleophilic substitution rivals that of the widely used halogen anions. Moreover, an alcoholic function can also act as a leaving group when transformed into a sulfonate ester and, in the last years, vinyl or aryl sulfonates have attracted increasing attention as the electrophilic partner in metal-catalyzed reactions (Scheme 17.2, path b). By means of this approach, Ar-X bonds (X = C, N) have been easily formed by metal-catalyzed activation of the Ar-O bond [1]. However, this is not the same for phosphate esters, which are virtually unused in the synthesis except when activated by a benzyl or a vinyl group and again under metal catalysis (Scheme 17.1, path a) [2].
