Esters sulfonic acid, polymer-supported

In an opposite manner to bases such as 1 and 2 in terms of reactivity, polymer-supported tosyl chloride equivalent 14 is able to capture alcohols as polymer-bound sulfonates 15, which are released as secondary amines, sulfides and alkylated imidazoles with primary amines, thiols and imidazoles as nucleophiles in a substitution process (Scheme 6) [24]. This technique has further been extended for the preparation of tertiary amines [25] and esters [26]. Excess of amine was scavenged by polymer-supported isocyanate 16 [27, 28] while excess of carboxylic acid was removed by treatment with aminomethylated polystyrene 17. 

Obrecht described the reaction of resin-bound thiouronium salt 111 vrith oxophe-nylbutynoic acid tert-butyl ester. Cleavage from the support was effected by S-oxidation to the sulfone followed by displacement vrith an amine [132]. The thiouronium salt pathway is illustrated in Scheme 26. Later, Masquelin et al. developed a condensation of resin-bound thiouronium salts with methylenemalononitriles to provide polymer-bound alkylthiopyrimidines 110 [133]. Pyrimidine derivatives 112... 

Furthermore, the presence of the sulfonate groups makes these polymers soluble in water in both the doped and undoped states [79,80]. Due to the failure to electro-polymerize these monomers in their acidic or sodium salt forms, the polymers have been prepared by polymerization of the corresponding methyl esters and subsequent conversion into the polyelectrolytic form [79]. This problem was not observed with 3 -propanesulfo-nate-terthienyl (28), which, unlike the parent monomers, can be electropolymerized without supporting electrolyte, thus providing unequivocal evidence of self-doping [34]. More recently, poly(3-thiophene-/3-propanesulfo-nate) (27b) was directly obtained by a chemical polymerization [81]. Attempts to prepare self-doped PTs from 3-(oj-carboxyalkyl)thiophenes (30) have also been reported [82]. These monomers are easily electropolymer-... 

---