C=S double bonds

The conversion of a thiolactone to a cyclic ether can also be used as a key step in the synthesis of functionalized, stereochemically complex oxacycles (see 64—>66, Scheme 13). Nucleophilic addition of the indicated higher order cuprate reagent to the C-S double bond in thiolactone 64 furnishes a tetrahedral thiolate ion which undergoes smooth conversion to didehydrooxepane 65 upon treatment with 1,4-diiodobutane and the non-nucleophilic base 1,2,2,6,6-pentamethylpiperidine (pempidine).27 Regio- and diastereoselective hydroboration of 65 then gives alcohol 66 in 89 % yield after oxidative workup. Versatile vinylstannanes can also be accessed from thiolactones.28 For example, treatment of bis(thiolactone) 67 with... 

Compounds with a thiocarbonyl a to the S-S bond such as the dithiuram (e.g. 8f2Al and xanthogen disulfides (e.g. 9)M have transfer constants that are much higher than other disulfides. In part, this may be due to the availability of another mechanism for induced decomposition (Scheme 6.9) involving addition to the C S double bond and subsequent fragmentation. Thiocarbonyl double bonds are very reactive towards addition and an addition-fragmentation mechanism has been demonstrated for related compounds (Section 6.2.3.5). 

The trend in relative effectiveness of RAFT agents with varying Z is rationalized in terms of interaction of Z with the C=S double bond to activate or deactivate that group towards free radical addition. Substituents that facilitate addition generally retard fragmentation. O-Alkyl xanthates (Z=0-alkyl, Table... 

Thiourea Ugands can be bounded to the metal centre through one nitrogen atom, the sulfur atom, or the C = S double bond. These coordination modes were studied by density functional theory calculations for Rh-thiourea complexes (Scheme 13). No stable structure was attained by optimisation of the nitrogen coordination mode I but optimised geometries as trigonal-bipyramidal complexes were obtained for modes II and III. An coordination is determined for the latter complex through both S and C atoms. As this... 

Most Naturally Occurring Unsaturated Fatty Acids Have c/s Double Bonds... 

Figure 10.8 Nanotube formation upon introducing a c/s-double bond in a diaminopyridine alkylamide and their corresponding alkyl chain packing in DAP-2. Reprinted with permission from [75] (2004) American Chemical Society.

Figure 10.9 Unsaturated glycolipids with varying positions ofthe c/ s-double bond and the corresponding EF-TEM images ofthe self-assemblies (a) 13-c/s (b) ll-c/ s (c) 9-cis ...

Figure 10.11 Adaptive response nature of c/s-double bonds in N-cardanyltauramide that undergoes micelle-vesicle-micelle transition with respect to temperature.

Dimethyl-3-methylenepyrrolidine-2-thione, which reacts with nitrones regio- and stereoselectively at its exocyclic C=C bond to give only spirocy-cloadducts 116, behaves more complicatedly with nitrile oxides. The latter undergo 1,3-dipolar cycloaddition both to the exocyclic C=C and C=S double bonds with subsequent cycloreversion and formation of spiro-lactams 117 (281). 

Apparently, the reaction involves cycloaddition of nitronate at the C=S double bond of thioketene. This approach can be useful for deoxygenation of labile nitronates. 

Intermolecular [3 + 2]-Addition to other Dipolarophiles Data on this problem are scarce and concern primarily interactions of SENAs with the C,S double bond. (383-386)... 

They proposed a mechanism as shown in Scheme 10, because they found close contact between the oxygen atom of the C=0 group and the carbon atom of the C=S group in a range of 2.77-2.86 A. These contacts are well below the sum of the van der Waals radii for oxygen and carbon (3.22 A). Thus, in the crystalline state, the oxygen atom is ideally positioned for excited-state nucleophilic attack on the C=S double bond, and this process may be the first step of the mechanism by which thiobenzanilides are formed in this medium. This would lead reversibly to the 1,3-oxazetidinium ion 18, which could react with water present in the medium and then break down, via species 19, to the enol of thiobenzanilide 16 and 3-phenylpropanoic acid 17. 

It is worth mentioning that fluorothiocarbonyl isothiocyanate, produced by the reaction of CSFCl with metal thiocyanates (52), combines with chlorine quantitatively at low temperatures at the C=S double bond, without suffering an attack on the isothiocyanate group 21) ... 

In an attempt to add sulfenyl halides to the C=S double bond, only the unsymmetrical disulfanes are formed, instead of mercapto-substi-tuted sulfenyl halides (54, 56, 72), e.g.,... 

Oxidation Carbon-Sulfur Systems. The most common metabolic process that affects a C-S system is S-oxidation. The S atom is oxidized to a sulfoxide. In the case of thioketones, the C=S double bond is converted to a C=0 bond. For thioethers, oxidative S-dealkylation is a possibility. 

Another type of cyclization reported in CHEC-II(1996) involves sulfonamides 240 and 241 as three-atom components and electrophilic C=0 or C=S double bonds, mainly those of heterocumulenes, affording 1,4,2-oxa/ thia)2-azoline-l,1-dioxide derivatives 242-246 (Scheme 33) <1996CHEC-II(4)534>. 

Benzo[7]thiete 41 reacts in the ortho-qumoiA isomer 41 with cyclic trithiocarbonates such as l,3-dithiolane-2-thione, (ethylene trithiocarbonate), l,3-dithiole-2-thiones, and adamantanethione <1997LA1603>. In boiling toluene, 1,3 dithiolane and dithiole derivatives formed the spiro compound 42 and 43 in good yield. The related l,3-dithiole-2-thiones reacted chemoselectively at the C=S double bond. The use of adamantanethione yielded the polycyclic adduct 44 in a smooth and quantitative reaction (Scheme 3). 

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