Vinyl dithiocarbamates

The use of heteroaryl vinyl sulfides and vinyl dithiocarbamates (166) as hetero-Michael addition acceptors has been described. Combined chelating and electron-withdrawing effects were postulated to stabilize the transient anionic species and allow smooth Michael-induced ring closure to produce C-glycosides (167).191... 

O-Alkyl xanthates and A -ary l-A -alkyl dithiocarbamates are effective with vinyl acetate. 97 Dithioesters and trithiocarbonates give severe retardation or even inhibition which is attributed to slow fragmentation of the adduct radical. 

In a series of papers, Matsuda et al. [291-295] employed RAFT-SIP with immobilized benzyl N,N-diethyldithiocarbamate to form polymer brushes from styrene, methacrylamides, acrylamides and acrylates, NIPAM and N-vinyl-2-pyrrolidone on various surfaces. The SIP is initiated by UV irradiation of the surface-bonded dithiocarbamates. Thermoresponsive polymer brushes were prepared by the polymerization of NIPAM and investigated by XPS, wetting experiments and mainly SPM [294]. Patterned polymer brush layers were also prepared. When chloro-methyl styrene was used as a comonomer, RAFT-SIP resulted in branching. By control of the branching, spatio-resolved hyperbranching of a controllable stem/ branch design was realized (Fig. 9.32) [293, 295]. 

Another entry to 1,3-dithiolylium salts starts from 5-vinyl Af,iV-dialkyl dithiocarbamates (239) which are easily obtained by reaction of sodium dithiocarbamates with 1,2-dibromoethane. Treatment of the dithiocarbamates (239) with bromine gives the 1,3-dithiolylium bromides (242) via the intermediates (240) and (241) (73CL867). 

A second populous class of T/2-vinyl complexes has resulted from addition of phosphines, phosphites, isonitriles, and thiolates to neutral d4 alkyne complexes. In particular, recent extensive work by the Davidson group with CpM(CF3C=CCF3)2X (97,176) and other hexafluorobutyne reagents has clarified much of this chemistry. We turn to this realm of Tj2-vinyl chemistry after first considering the one class of dithiocarbamate alkyne complexes known to form tj2-vinyl ligands. 

Monodentate carboxylates 02CR, dithiocarbamates S2CNR2, amidates RC(NR)2, alkyl, aryl, vinyl (alkenyl), acetylide (alkynyl), formyl, acyl, aroyl. 

Dithiocarbamate-iunctionalized polymers of styrene and MMA at both ends are prepared [148] by thermal free radical initiation with tetraethylthiuram disulfide which is known [146] to behave as initiator, chain transfer agent and terminator (iniferter). Successive photolysis of the terminal dithiocarbamate end groups, in the presence of another vinyl monomer, allows one to obtain three-block cc lymers (Scheme 43). 

By a similar approach 5-vinyl-A7,A7-dialkyl-dithiocarbamates (214) afford, upon reaction with bromine, the 1,3-dithiolylium bromides (215) (Equation (35)) <73CL867,75S277>. 

Dithiole-2-one (60), which can be readily transformed into its thio- or seleno-carbonyl derivatives, is a key intermediate for the synthesis of tetrathiafulvalene (Scheme 13)[31]. We first anticipated that compound 57, a Michael addition product of xanthate 54 to vinyl sulfoxide, might be an ideal intermediate for the synthesis of 60 via cyclization under Pummerer rearrangement conditions. However, although Michael addition of dithiocarbamate 53 to vinyl sulfoxide proceeded smoothly to yield compound 55, the addition reaction with xanthate 54 failed. We then turned to the alkylation approach. Xanthate 54 was alkylated smoothly with 56, which served as the synthetic equivalent of the vinyl sulfoxide, in ethanol under sonication in 90% yield [32]. Cyclization of 57 under Pummerer rearrangement conditions in the presence of trifluoroacetic acid afforded 58 in 79% yield. Sodium metaperiodate oxidation gave the unstable sulfoxide 59 which underwent thermal elimination to yield 60 in refluxing benzene in moderate yield. 

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