Vinyl, from thiols addition

In contrast to oxygen, sulfur has been far less widely used as a nucleophile for addition to ruthenium vinylidenes. The formation of vinyl thioethers from the addition of thiols to aUcynes catalyzed by binuclear ruthenium complexes Cp Ru (p-SR)2RuCp (R=Et, i-Pr, f-Bu) and related complex Cp Ru(p -C6F5)(p-S) (p-SC6F5)RuCp has been described [112]. 

Thiol-yne radical reactions follow a similar initiation step to that of thiol-ene reactions. After the initial addition of a thiol to the alkyne and formation of a vinyl radical with a P-thioether function, a hydrogen abstraction from another thiol molecule generates a new thiyl radical. Subsequent addition of a thiyl radical on the vinyl thioether forms another carbon radical, which abstracts a hydrogen from another thiol molecule to give a 1,2-dithioether, and the thiyl radical generated reenters the chain process (Scheme 1.11). The addition of the first thiol to the alkyne is the rate-limiting step, and the second thiol addition to the intermediate thiol-alkene is a faster step. Studies revealed that the second addition is approximately three times faster than the first addition [45]. 

PSL, AMANO) has been found to catalyze the Markovnikov-type addition of thiols to vinyl esters (Scheme 5.23) [114] and acylases aminoacylase [115], penicillin G acylase [116], and acylase from AspergiUus oryzae [117], the same kind of addition of various nitrogen nucleophiles. Unfortunately, most additions described above are nonstereoselective. 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

The preceding study has demonstrated [2.2.1]bicycloheptenyl functionalized resins can be useful and interesting ene components in photoinitiated thiolene polymerizations. The addition of thiols to the unsaturation of this bicyclic system appears to be rapid and exothermic. The relative rates of this addition compared with allylic derivatives and vinyl ethers are quite favorable. The organic resins can be readily prepared from either polyols, f>olyamines, or acrylic precursors (Figure 10) and the yields are generally quite good. When acrylate esters are used as precursors, the cycloaddition reaction occurs spontaneously and no catalysis of the reaction is necessary. 

Alkylthioethyl acetates can be formed from vinyl acetates by the addition of thiols with BF3-OEt2 as the catalyst. The yield is 79%, compared to 75% when BF3-OEt2 is used in conjunction with Mercury(II) Sulfate or Mercury(II) Oxide. 

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