Alkyl thioacrylates

Nakayama, Tsututa, Furuakawa and Kawasaki (46) have studied the stereospecific anionic polymerization of a series of alkyl thioacrylates. They found that the M-propyl, i-propyl, w-butyl, i-butyl, -sec.-butyl, and /-butyl thioacrylates gave crystalline polymer. The ethyl compound gave amorphous polymer. 

Marvel and co-workers [7] were one of the first groups to study in detail the preparation and polymerization of alkyl thioacrylates. Mikeska [8] earlier prepared thioacrylic esters by the reaction of chloropropionyl chloride and the mercaptan followed by dehydrohalogenation with diethylaniline. Marvel prepared alkyl thioacrylates by the reaction of a,yS-dibromopropionyl chloride with mercaptan followed by the reaction with sodium iodide to eliminate the bromine atoms to give the acrylate ester. 

The stereospecific polymerization of alkyl thioacrylates has also been reported using n-butyllithium [11]. 

The a-addition of alkyl or aryl thionucleophiles R H to y9-nitroacrylates R2(NC>2) C=CC02R3 in THF in the presence of Et3N or DBU does not stop at y9-nitro-o -thioalkanoates R2CH(N02)CH(SR1)C02R3, but proceeds further with concomitant elimination of nitrous acid to afford a-thioacrylates R2CH=C(SR1)C02R3.191... 

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). 

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