Sensitizers thiocarboxylates

DCC can be used to prepare 5-alkyl and 5-aryl thiocarboxylates (1) from carboxylic acids and thiols according to equation (5). This method has been successfully applied to the synAesis of thiol esters with sensitive substituents, e.g. 5-methyl thioacrylate, a natural product. In particular, N-protected amino acid and peptide 5-phenyl esters, which are useful building blocks in peptide synthesis, are obtained in excellent yields without racemization. N-Hydroxyphthalimide and DMAP have been used as cocatalysts to facilitate the reaction. The preparation of the Wittig reagent (5) by this route is shown in equation (6). 

The anions of such cesium salts as cesium thioacetate or cesium benzoate often undergo extremely clean Sn2 substitution reactions. Optically active thiols, especially those sensitive to racemization, can be prepared using cesium thiocarboxylates as nucleophiles. The reaction of ethyl (i )-0-mesylmandelate (64), readily prepared from the commercially available... 

After irradiation, the HABI molecules decompose into lophyl radicals which subsequently abstract protons from a donor, e.g. thiols [BER 14] (Figure 4.9), heteroaromatic thiols, benzothiazoles, benzooxazoles, tertiary amines, alcohols, thiocarboxylic acids [BLA 09] or dyes [BEN 02], If used in a dental composite, they lead to improved compressive, yield and flexural strengths compared to conventional composites with CQ/DMABE. Furthermore, the sensitivity to ambient light could be decreased [BLA 09]. 

---