Sulfur-based nucleophile

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). 

Scheme 33 Conjugate addition of sulfur based nucleophiles...

Pyrazines undergo nearly all of the same reactions as pyrimidines, from nucleophilic substitution (SnAt) to palladium-catalyzed cross coupling reactions. Displacement of the chlorides via SnAt reactions with nitrogen (157 158) and sulfur-based nucleophiles (158... 

The reaction of C 4-acetoxylated catechin 517 and epicatechin with nucleophiles under Lewis acid conditions to yield C-4-elaborated flavan-3-ols 518 has been described. The C 4 acetoxy group is activated by a Lewis acid, such as BFj-OEo or TMSOTf, allowing delivery of a variety of carbon-, nitrogen-, and sulfur-based nucleophiles in stereoselective fashion to this position (Scheme 94) <2002TL7753>. An SnI mechanism was invoked for the process. Table 4 displays the results for catechins. 

Table 2.8 compares hydrolysis half-lives with half-lives for reaction with sulfur-based nucleophiles for several halogenated aliphatics. These data show that the environmental half-lives for substrates such as 1-bromohexane and 1,2-dibromoethane can be substantially reduced in the presence of HS and polysulfides. Enhanced degradation of 2-bromopropane and 1,1,1-trichloroethane, as well as chloroform and carbon tetrachloride (results not shown) was not observed, suggesting that steric hindrance significantly impedes reaction with the sulfur based nucleophiles (Haag and Mill, 1988a). 

Myers AG, Herzon SB (2003) Identification of a novel Michael acceptor group for the reversible addition of oxygen- and sulfur-based nucleophiles. Synthesis and reactivity of the 3-alkylidene-3H-indole 1-oxide function of Avrainvillamide. J Am Chem Soc 125 12080-12081... 

The asymmetric conjugate addition of sulfur-based nucleophiles to Michael acceptors has been achieved using enantiomerically pure metal-based catalysts and organocatalysts. Sulfur nucleophiles are soft, and preferentially react by conjugate addition with a, p-unsaturated carbonyl compounds. Only catalytic amounts of the lithium thiolate (11.65) are required, since addition to the enone (11.66) generates the enolate (11.67). The enolate is then able to deprotonate thiol (11.68), regenerating thiolate (11.65) with formation of the product (11.69). 

Ring-Opening meso-Oxabicyclic Alkenes with Sulfur-Based Nucleophiles 423... 

TABLE 4. Sulfur-Based Nucleophiles Reported to React with AUylic Carbonates... 

Mechanism of action. Acrolein has two functional groups that can contribute to its biocidal activity. It is an a, jS-unsaturated aldehyde and as such the carbon-carbon double bond is extremely reactive. Nucleophiles, typically sulfur based nucleophiles, can react with the terminal carbon in a Michael type reaction (March, 1992), while the aldehyde group can undergo reactions typical of all aldehydes. From a biocidal point of view, those sulfur-based nucleophiles would include cysteine residues of the cell wall and those proteins associated with the cell wall. The amine containing amino acids (lysine and arginine) may also react with the aldehyde group of acrolein. 

Starting from vescalagin (34), all of the condensation reactions we performed using various carbon-, oxygen-, and sulfur-based nucleophiles occurred with retention of configuration at C-1, that is, the newly formed bond is still (3-oriented (see Section 4.3). As these chemical reactions produce ellagitannin derivatives with the same Cj-configuration as that of... 

In 1997, the Sundararajan group reported a heterobimetallic complex Al-Li-(21a)2 as a promoter for the asymmetric sulfur-Michael addition of thio-phenols to cyclic enones with 96-97% yields and 26-45% enantiomeric excess. " Later in 2001, they described a new polymer-anchored chiral catalyst Al-Li-(28)2 for the addition of thiols to cycloalkenones (Scheme 19.36). With thiophenol and p-methylthiophenol as the sulfur-based nucleophiles, the adducts were obtained in excellent yields but moderate enantioselectivities (33-57% enantiomeric excess). 

Direct nucleophilic substitution of the hydroxyl group of ferro-cenyl alcohols has also been disclosed. Very low catalyst loadings were sufficient for the substitution with various carbon-, oxygen-, nitrogen-, and sulfur-based nucleophiles (eq 5). ... 

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