Sulfur-stabilized

The initiating step in these reactions is the attachment of a group to the sulfoxide oxygen to produce an activated intermediate (5). Suitable groups are proton, acyl, alkyl, or almost any of the groups that also initiate the oxidations of alcohols with DMSO (40,48). In a reaction, eg, the one between DMSO and acetic anhydride, the second step is removal of a proton from an a-carbon to give an yUde (6). Release of an acetate ion generates the sulfur-stabilized carbonium ion (7), and the addition of acetate ion to the carbonium ion (7) results in the product (eq. 15) ... 

Second-row elements, particularly phosphorus and sulfur, stabilize adjacent carba-nions. The pATs of some pertinent compounds are given in Table 7.10. 

Discuss the relevance of these observations to the structure of sulfur-stabilized carbanions and rationalize your conclusion about the structure of the carbanions in MO terms. 

Enolates of aldehydes, ketones, and esters and the carbanions of nitriles and nitro compounds, as well as phosphorus- and sulfur-stabilized carbanions and ylides, undergo the reaction. The synthetic applications of this group of reactions will be discussed in detail in Chapter 2 of Part B. In this section, we will discuss the fundamental mechanistic aspects of the reaction of ketone enolates with aldehydes md ketones. 

Sulfur-stabilized ylides underwent photodriven reaction with chromium alkoxy-carbenes to produce 2-acyl vinyl ethers as E/Z mixtures with the E isomer predominating (Table 22) [ 121-123]. The reaction is thought to proceed by nucleophilic attack of the ylide carbon at the chromium carbene carbon followed by elimination of (CO)5CrSMe2. The same reaction occurred thermally, but at a reduced rate. Sulfilimines underwent a similar addition/elimination process to produce imidates or their hydrolysis products (Table 23) [ 124,125]. Again the reaction also proceeded thermally but much more slowly. Less basic sulfilimines having acyl or sulfonyl groups on nitrogen failed to react. 

Table 22 Photo-driven reaction of sulfur-stabilized ylides with alkoxycarbenes...

The direct addition of simple alkyl groups onto aldehydes is the most challenging in water. Mitzel reported the indium-mediated alkylation of carbonyl compounds with a-sulfur stabilized systems.224 Recently, Li and co-workers reported an efficient addition of simple alkyl halides to aldehydes mediated by Zn/Cul with a catalytic amount of InCl in water (Eq. 8.89).225... 

Sulfur stabilized carbanions Heterocycle stabilized carbanions... 

The ligand (298), coordinating through phosphorus and all three sulfurs, stabilizes iron(IV) in [Fe(298)Cl], which is the first stable trigonal bipyramidal iron(IV) complex to be prepared. 

Adamantanedimethylium dications 236 Bicyclo[3.3.3]undecane-l,5-diyl dication (manxyl dication) 238 A sulfur-stabilized carbodication 238... 

Miller and coworkers have recently prepared a sulfur-stabilized carbodication, 1,3,5,7-tetramethyl-2,4,6,8,9-pentathiabicyclo[3.3.l]nonane-3,7-diylium dication (103). 

Radical cations of 2-alkylidene-l,3-dithianes can be generated electrochemically by anodic oxidation using a reticulated vitreous carbon (RVC) anode <2002TL7159>. These intermediates readily react with nucleophiles at C-1. Upon removal of the second electron, the sulfur-stabilized cations were trapped by nucleophilic solvents, such as MeOH, to furnish the final cycloaddition products. Hydroxy groups <20010L1729> and secondary amides <2005OL3553> were employed as O-nucleophiles and enol ethers as C-nucleophiles (Scheme 50) <2002JA10101>. 

TABLE 4. Generation of sulfur-stabilized anion with organometaUic reagents... 

Composition (wt. %) NH4CIO4 67 aluminum 17 CuO202, a burning rate accelerator 0.1 sulfur, stabilizer 0.1 N-phenylnaphthylamine, stabilizer 0.1 Fe(AA)3 0.015 HAA 0.009 polyether-polyurethane binder containing 25% isodecyl pelar-gonate 15.68%. 

A new method for the synthesis of 2-substituted, as well as 2,4- and 2,5-disubstituted, cyclopentanones in 53-93% yield has been reported.81 For example, the Lewis acid catalyzed transformation of l-propanoyl-l-(4-tolylsulfanyl)cyclobutane gave 2-ethyl-2-(4-tolylsulf-anyl)cyclopentanone (1) in 93 % yield. The formation of the cyclopentanone is best explained by a mechanism which involves initial coordination of aluminum trichloride to the carbonyl oxygen, followed by ring expansion to form the sulfur-stabilized carbocation. Finally, migration of the ethyl group to the carbocation center regenerates concomitantly the carbonyl function.81... 

Bordoloi, . K. Pearce, E. M. "Plastic Sulfur Stabilization by Copolymerization of Sulfur with Dicyclopenta-diene" ADV. CHEM. SER. 1978, 165, 31. 

Sulfur stabilized nitrenes have been implicated in aziridination, e.g. (4) + (5) — (6) (94CPB27). Oxynitrenes derived from the oxidation of alkoxyamines are known, but are generally less efficient in aziridination. 

Sulfur-stabilized copper-zinc carbanions have been used [299] by Knochel et at A first type obtained from the reaction of the Simmons-Smith reagent with a copper(i) thiolate was treated with a... 

Most of the applications of sulfoxides in synthesis make use of the reactions of sulfur-stabilized carbanions with electrophiles [385, 386]. Thus the methylsulfinyl methylene carbanion, conveniently generated through the interaction of sodium hydride with DMSO [387], is a powerful nucleophile. 

From oxidative cleavage of 1,2-diols and 1,2-amino alcohols Dibutyltin oxide, 95 By reaction of alkyl halides with sulfur-stabilized carbanions Methylthiomethyl p-tolyl sulfone, 192 From reduction of carboxylic acids Vilsmeier reagent, 341 From terminal alkenes by addition reactions... 

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