Silyl sulfides

Palladium dimethylsilanedithiolato complex is a precursor for Ti—Pd and Ti—Pd2 heterometal-lic complexes.311 The bis-silyl sulfides (R3Si)2S have been widely used to prepare a variety of metal sulfide clusters, because these reagents exploit the strength of the Si—O and Si—Cl bond to... 

Since the silyl sulfide is very water-sensitive, all glassware should be dried carefully. 

The following routes to unsymmetrical disulfides and symmetrical trisulfides use silyl sulfides and thiosulfinates [41.42]. Thiosulfonates react similarly. 

Another route which has recently been used to generate thiocarbonyl ylides involves the bromodesilyl-ation reaction of a-bromosilyl silyl sulfide (189). This process is related to the methodology first developed by Padwa for the preparation of azomethine ylides. Thus, heating a sample of (189) generates thiocarbonyl ylide (190) which can be trapped with various dipolarophiles to give cycloadducts of type (191 Scheme 44). 

The iron-catalyzed reaction of propargyl sulfides 66 and trimethylsilyldiazomethane 67 delivers allenyl a-silyl sulfides 68 [44]. 

The simple reductive lithiation and quench of dithioacetals means that a-functionalised - and in particular, a-silylated sulfides are very easy to prepare. Cohen has exploited this in a number of ways for example, a ketenedithioacetal 70 can be used to generate an a-lithiovinylsilane 71 if a silyl halide is used as the electrophile in the first step.85... 

Ricci and co-workers showed that it is possible to transform a wide range of acylsilanes 2 into the corresponding thioacylsilanes 1 by reaction of bis(trimethyl-silyl)sulfide in the presence of CoC12-6H20 under very mild conditions and in good yields (Table 2)19 (Scheme 2). 

Appreciable diastereoselectivity (50%) was found in the cycloaddition with buta-1,3-diene at -78 °C and the protiodesilylation of the diastereomeric mixture of the adducts with TBAF gave dihydrothiopyran with 51% ee (Scheme 28). Similar diastereoselectivity was observed in the reaction with organo-lithium and Grignard reagents which gave a-silyl sulfides in moderate yields with medium to good levels of asymmetric induction (de = 40-76%).45 As an example, the derivative with E = D gave with protiodesilylation a-deuterio benzyl methyl sulfide with 45% ee. These results lead to the conclusion that in both cases protiodesilylation occurs stereospecifically without loss of the induced chirality (Scheme 28). 

The difference in reactivity between the a-stannyl sulfide 16A and the a-silyl sulfide 16B can be explained by comparing the two-center energies of their carbon-metal bonds. Semiempirical molecular orbital calculation revealed that the bond energies decrease in the order of 2-silyl, 2-germyl, and 2-stannyl-1,3-dithiane cation radicals. As the silyl dithiane was completely consumed by the oxidation under the... 

Zinc bromide catalysis effects a similar aminomethylation of silyl sulfides and phosphites (equation 11). ... 

Alknyl silyl sulfides, R C=CSSiR 3, which are readily obtained by silylation of anions (39), react as thioketene equivalents. Thus, (3-thiolactams are formed in the reaction with C=N systems (c/. Volume 5, (Chapter 2.2) and thioamides on addition of amines equation (18) shows a typical example. This approach has great promise for the thioacylation of very sensitive natural products. 

Detailed electrochemical studies and the detection of crossover disulfide products in mixed electrolyses support the first mechanism [178]. Cleavage of an a C-Si bond on oxidation of a-silyl sulfides to give phenylthio carbocations as shown in Eq. (34) M=SiMe3 is known [179-182] ... 

Table 5. Oxidation potentials of a-silyl sulfides and reference compounds ...

Thus irradiation of 168 or 169 in the presence of 1,4-naphthalenedicarbonitrile gave 170 and 171 in 84 and 61% yields, respectively [323]. The mechanism for these reactions is analogous to that suggested for the preceding examples but the yields for the a-silylated sulfides proved far inferior to those of the corresponding a-stannyl sulfides. 

Thioamides. By activation of the substrate with phosphoryl chloride before treatment with the silyl sulfide, amides and lactams can be converted to the thio analogs under extremely mild (—78 C) conditions without the need for a catalyst. 

Without additional reagents Reactions with silyl sulfides Dimethyl mercaptals from oxo compds. under neutral conditions... 

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