Sulfur nucleophiles formation

Nucleophilic addition of sulfur nucleophiles formation of thioacetals... 

However, formation of this bond through the conjugate addition of a soft sulfur nucleophile to a,P-unsaturated aldehydes is efficiently catalysed using iminium ion catalysis [116], Using diarylprolinol silyl ether 55 the addition of a series of sulfur based nucleophiles to a variety of a,P-unsaturated aldehydes was shown to be effective (73-87% yield 89-97% ee). The products were isolated as their p-hydroxy sulfide derivatives 73 after in situ reduction of the products (Scheme 33). 

Similar reactivity is known for divalent sulfur nucleophiles (75JA3850). For 3,3-dimethyl-1,2-dioxetane, initial attack at carbon by azide ion has been postulated to explain the formation of acetone and nitrogen and imine TV-oxide (Scheme 40) (71TL749,72JA1747). 

Sulfur nucleophiles such as thiolate anion generally appear near the top of the nucleophi-licity scale and thus readily attack oxepins (Scheme 20). While adduct formation between oxepin (7) and thiols occurs spontaneously upon mixing (74JA6929), a similar reaction between the naturally occurring tripeptide thiol, glutathione, and oxepin-arene oxide intermediates formed during mammalian metabolism is catalyzed by a glutathione epoxide transferase. 

The synthesis of thiepanes by double nucleophilic reaction in dipolar aprotic solvents improves the yield even under at normal dilution (79SC857). Li2S generated in situ from hexamethyldisilathiane and methyllithium was convenient for carbon-sulfur bond formation (Equation (2)) (85JOC4969). 

The photolysis of 1,2,4-oxadiazoles in the presence of sulfur nucleophiles has been shown to afford 1,2,4-thiadiazoles. N—S bond formation between the ring species and the sulfur nucleophile is thought to account for the observed products.96 A review has appeared which includes an account of the rearrangement of 1,2,3-thiadiazoles to other heterocycles such as 1,2,3-triazoles and 1,2,3,4-thiatriazoles.97... 

The cyclopentene annulations can also occur in the reactions of alkynyliodo-nium salts with nitrogen- and sulfur nucleophiles (Scheme 61). Specifically, azi-docyclopentene 155 is formed upon treatment of octynyliodonium tosylate 154 with sodium azide in dichloromethane [123]. The reaction of alkynyliodonium salt 156 with sodium toluenesulfinate results in the formation of substituted indene 157 via alkylidene carbene aromatic C-H bond insertion [124]. 

The Michael addition mechanism, whereby sulfur nucleophiles react with organic molecules containing activated unsaturated bonds, is probably a major pathway for organosulfur formation in marine sediments. In reducing sediments, where environmental factors can result in incomplete oxidation of sulfide (e.g. intertidal sediments), bisulfide (HS ) as well as polysulfide ions (S 2 ) are probably the major sulnir nucleophiles. Kinetic studies of reactions of these nucleophiles with simple molecules containing activated unsaturated bonds (acrylic acid, acrylonitrile) indicate that polysulfide ions are more reactive than bisulfide. These results are in agreement with some previous studies (30) as well as frontier molecular orbital considerations. Studies on pH variation indicate that the speciation of reactants influences reaction rates. In seawater medium, which resembles pore water constitution, acrylic acid reacts with HS at a lower rate relative to acrylonitrile because of the reduced electrophilicity of the acrylate ion at seawater pH. 

By contrast, 3-hydrazino-l,2,4-thiadiazoles (163), which are prepared by ring closure methods, are very sensitive to acids and undergo elimination of sulfur with formation of 5-arylamino-l,2,4-triazoles (164) as indicated in Scheme 61 (63JCS4566). The mechanism of this conversion is not known but presumably involves the attack of a hard nucleophile at the 5-position followed by ring opening, loss of sulfur and recyclization as has been observed with the quaternary salts (77JCS(P1)1791) (see Schemes 22, 23, and 24). Hydrazine (163) reacts with aldehydes to produce hydrazones (165) and with dimethyl malonate to yield pyrazoles (166). Diazonium salts of type (153) have been prepared by the methods... 

For sulfur nucleophiles, the intramolecular gold-catalyzed hydrothiolation of allenes was described in 2006. a-Thio-allenes led to the formation of 2,5-dihydrothiophenes in moderate to good yields and with complete stereoselectivity. ... 

Finally, aldehydes can react with nitrogen (31-32) and sulfur nucleophiles, including H2S, which may also be present in wines. These reactions may have dramatic effects on flavor and aroma (e.g., formation of ethyl mercaptan from acetaldehyde and H2S results in formation of a onion-like or burnt rubber aroma) and will decrease the levels of free aldehydes which can be readily quantitated (1). 

Carbon-Sulfenyl Sulfur Bond Formation 5.1.1. Addition of Sulfur Nucleophiles to Unsaturated Compounds 5.1.1.1. Addition of Thiols or Thioacids... 

The addition of sulfur nucleophiles to aldehydes and ketones may be exemplified by the formation of hydrogensulfite (bisulfite) adducts (3.12). These are sulfonates that are water soluble. However, their stcric bulk means that whereas they are formed from aldehydes and methyl ketones, more highly substituted ketones are reluctant to form these derivatives. 

Sulfur reacts with many organic molecules, and in such sulfur-sulfur bond-breaking reactions free radicals may be involved the reactions are often catalysed by amines and Lewis acids. Amines and other bases activate sulfur by formation of nucleophilic sulfur species, while Lewis acids cleave the sulfur-sulfur bond to give electrophilic sulfur moieties. 

By far most of the reports on addition reactions of hetero-nucleophiles to activated dienes deal with sulfur-nucleophiles " ° 20-t37 jjj particular in the synthesis of 7/1-sulfur-substituted steroids which, like their carbon-substituted counterparts (Section ILA), are of interest because of their ability to inhibit the biosynthesis of estrogens ° 129-137 Early investigations 120-122 concentrated on simple acyclic Michael acceptors like methyl sorbate and 2,4-pentadienenitrile. Bravo and coworkers observed the formation of a 3 1 mixture of the 1,6- and 1,4-adduct in the reaction of methyl sorbate with methanethiol in basic medium (equation 39). In contrast to this, 2,4-pentadienenitrile adds various thiols regioselectively at C-5, i.e. in a 1,6-fashion (equation 4O) 121.122, jjjg same is true for reactions of this substrate with hydrogen sulfide (equation 41), sodium bisulfite and ethyl thioglycolate. ... 

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