P-ketosulfides

The major part of the reactions of a-arylation which have been reported were performed on substrates containing active methylene groups, such as p-diketones, p-ketoesters, P-ketonitriles and malonic acid derivatives. Less activated compounds, such as P-ketosulfides have also been efficiently arylated on the a-carbon. (Table 5.3) The yield of the arylated product can be increased by addition of 1,1-diphenylethylene, acting as a free radical trap. For example, in the reaction of phenylation of ethyl cyclohexanonecarboxylate, addition of 1,1-diphenylethylene reduced the radical chain decomposition in such a way that an 80% yield was obtained instead of 55% in absence of 1,1-diphenylethylene. ... 

The absorption maximum around X 210 nm for simple dialkyl sulfides [11], corresponding to a n-o transition, experiences an important bathochromic shift for p-ketosulfides (X 240 nm) [12] due to a conjugative effect between the two functional groups. This interaction is illustrated in the spectra of 2H,6H-thiin-3-ones [13] and also of their corresponding 1-oxides [14], with the appearance of an additional absorption band around 275 nm that does not appear in the spectrum of e.g. 2fl, 6fl-pyran-3-ones [15] (Scheme 1). 

The highly enantioselective organocatalytic rearrangement of racemic a-acetoxy-P-ketosulfides (compounds that are easily obtained by Pummerer rearrangement of P-ketosulfoxides) to a-acetoxythioesters was reported by Frongia and coworkers in 2010 [36]. The process, which is formally a l,4-0,0 rearrangement of an acetyl group, can be conveniently catalyzed by quinidine 22 (Scheme 40.32). The proposed catalytic cycle, depicted in Scheme 40.33, involves the deprotonation of the... 

Scheme 40.32 Quinidine-catalyzed rearrangement of a-acetoxy-p ketosulfides to...

P-sulfonyl 857 a-acetoxy-P-ketosulfides 1207 -racemic 1207 a-acetoxythioesters 1207 N-acetylaminomalonate 502 acetylenes 1207... 

Scheme 40.33 Proposed mechanistic cycle for the rearrangement of a-acetoxy-P-ketosulfides.

PolyCy-benzyl L-glutamate) (PBLG), 15 109 Poly(y-ketosulfide)s, optically active, 23 711 Poly(P-alanine), 1 292 Poly-P-hydroxybutyrate (PHB), 12 482 Polybetaines, 20 479-482 applications of, 20 482 preparation of, 20 480-481 solution properties of, 20 481-482 synthesis of, 20 479-481 Polyborates, 4 256-258 Polyborosiloxanes, in silicon carbide manufacture and processing, 22 533 Polybrominated diphenyl ethers (PBDEs), 13 142-143 20 56... 

Ring expansion of the six-membered ketosulfide (371) produces both 5-thiocanone and 4-thiocanone [372 v 1700 cm-1 (neat)], but in low yields (70JOC584). The photochemistry of these ketones has been studied and leads to a variety of products in low yields (70JOC584). 3-Thiocanone (373 b.p. 66-68 °C/0.35 mmHg, v 1708 cm-1) is formed in 44% yield by the dihalide method, but in only 3% yield by the Dieckmann reaction under high dilution conditions (70JPR1058). 

The reactions were catalyzed under mild conditions in a short time. The silyl enol ethers reacted with activated acetals or aldehydes at -78 °C to give predominantly erythro- or threo-products, respectively [91, 92]. In the same way the aldol reaction of thioacetals, catalyzed by an equimolar amount of catalyst, resulted in y-ketosulfides [94] with high diastereoselectivity. The interaction of silyl enol ethers with a.P Unsaturated ketones, promoted by the trityl perchlorate, was shown to proceed regioselectively through 1,2- [96] or 1,4-addition [93]. Trityl salts were also... 

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