Thiolates conversion

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

Replacement of iodine in (perfluoroalkyl)ethyl iodides predominates over the usual conversion to olefins when the reagent is very nucleophilic and weakly basic Soft nucleophiles like sodium thiocyanate and sodium thiolates react well in displacements [46, 47] (equation 42)... 

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... 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

Another method for reductive dimerization has been developed in hy-drosilylation. NiCl2-SEt2 is an effective catalyst in silylative dimerization of aromatic aldehydes with a hydrosilane (Scheme 12) [40]. A catalytic thiolate-bridged diruthenium complex [Cp RuCl(/ 2-SPrI)2RuCp ][OTf] also induces the conversion to 1,2-diaryl-1,2-disiloxyethane [41]. A dinuclear (siloxyben-zyl)ruthenium complex is considered to be formed, and the homolytic Ru - C bond fission leads to the siloxybenzyl radicals, which couple to the coupling product 14. 

The thiolate species (182) and (183) do not require photo excitation in order to initiate polymerization (182) consumes 200 equivalents MMA in 18 h at 35 °C (Mn = 22,000, Mn(calc) = 20,000, Mw/ Mn= 1.12) 446 The propagating species is again believed to be an enolate.447 Propagation is accelerated upon addition of (185), with 100 equivalents of MMA requiring just 90 seconds for full conversion. The steric bulk of the Lewis acid prevents scrambling of the propagating enolate between the two aluminum centers.448 Hence, for aluminum diphenolates, ortho substitution is essential, whilst smaller Lewis acids such as Me3Al may only be used successfully at low temperatures, e.g., —40 °C. 

The corresponding thiolate (324) will also polymerize epoxides following photoinitiation 944 For example, using 190 equivalents of EO, a conversion of <2% was observed after 205 min in the dark. However, this rises to 97% if the system is irradiated for 80 min (Mn = 8,700, Mn calc = 8,100, Mw/Mn= 1.05). 111 NMR studies confirm that the propagating species is a metal-alkoxide and as a result, if irradiation is stopped once initiation has occurred, the polymerization will persist, although... 

Several Pd11 complexes with thiolate or thioether derivative ligands have been studied to be applied in the hydroxycarbonylation reaction.394 Aminothiolate complexes of palladium with PPh3 catalyze the conversion of styrene to 2-phenylpropionic acid in high yield and excellent regioselectivity.644 Under mild conditions and in the presence of a catalytic amount of an S, TV-chelated palladium or//zo-amino-arenethiolate complex, styrene reacts with CO and oxalic acid or water to selectively give 2-phenylpropanic aid in high yield.645... 

The final method for constructing epidithiodiketopiperazine motifs relied on the nucleophilic thiolation of /V-acyliminium ions. Access to alpha-oxidized diketopi-perazine structures was central to this approach, and key developments were made in this regard. Schmidt first demonstrated the feasibility of this ionization approach in 1973 by conversion of proline anhydride to its diacetate using Pb(OAc)4 [42], Hydrolysis of the acetates, ionization of the hemiaminals with zinc chloride in the presence of hydrogen sulfide, and oxidation with iodine provided the epidisulfide of interest. In 1975, Matsunari reported access to alpha-methoxy diketopiperazines,... 

SIBBESEN, O., KOCH, B., HALKIER, B.A., M0LLER, B.L., Cytochrome P450TYr is a multifunctional heme-thiolate enzyme catalyzing the conversion of 1-tyrosine to p-hydroxyphenylacetaldehyde oxime in the biosynthesis of the cyanogene glucoside dhurrin in Sorghum bicolor (L.) Moench, J. Biol. Chem., 1995, 270, 3506-3511. 

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. 

As shown in Table IV, a number of well-known, single-site, ionic PTCs also catalyze the aromatic fluoroalkoxylation reaction, albeit at somewhat higher molar ratios than that required for the optimum conditions using PEG-8000. The most effective of these ionic materials was tetrabutylphosphonium bromide (TBPB) which is in agreement with a study by Bruneile (34c) on the PTC-mediated reaction of thiolates with polychlorobenzenes. It is interesting to note that solid-liquid conditions generally provided better conversions for the ionic PTCs than liquid-liquid conditions and that water... 

The use of six equivalents of dihydrogen peroxide leads to a clean conversion of the dithiolate complex to the disulfonate compound. Earlier studies on oxidation of nickel thiolates showed that oxidations with dioxygen stop at monosulfinates. Our observation and the characterization of the first chelating bis-sulfonato nickel complex formed from the direct oxidation of a mononuclear nickel dithiolate, may also provide new insight into the chemistry of sulfur-rich nickel-containing enzymes in the presence of oxygen. 

This heme-thiolate-dependent enzyme [EC 1.14.15.4], also known as steroid 11/3-monooxygenase, catalyzes the reaction of a steroid with reduced adrenal ferredoxin and dioxygen to produce an 11/3-hydroxysteroid, oxidized adrenal ferredoxin, and water. The enzyme also catalyzes the hydroxylation of steroids at the 18-position and can catalyze the conversion of 18-hydroxycorticosterone into aldosterone. 

This heme-thiolate-dependent enzyme [EC 5.3.99.5] catalyzes the conversion of (5Z,13E)-(155 )-9a ,lla -epidi-oxy-15-hydroxyprosta-5,13-dienoate to (5Z,13 )-(155)-9o ,llQ -epoxy-15-hydroxythromba-5,13-dienoate. Thus, it converts prostaglandin H2 into thromboxane A2. 

Araki et al. have found that La wesson s reagent, 2,4-bis(4-methoxyphenyl)-l,3-dithiaphos-phetane-2,4-disulflde, provides a convenient one-step conversion of mesoionic olates to mesoionic thiolates <88BCJ2977>. Thus 3-phenyl-1,2,3,4-thiatriazolium-5-olate (170) was converted to (171) in high yield by refluxing for 50 min in benzene (Equation (14)). This eompound had previously been prepared from compound (161 R = Ph) by treatment with sodium sulfide in aqueous dimethyl-formamide at room temperature <79JCS(Pi)732>. 

Robert and co-workers (239,240) discovered novel conversions of 2-amino-1,3-dithiolium-4-olates (348) into other mesoionic heterocycles. For example, reaction of 348 with carbon disulfide, phenyl isocyanate, or phenyl isothiocyanate affords l,3-dithiolium-4-thiolates (349), l,3-thiazolium-4-olates (350), and 1,3-thiazolium-4-thiolates (351), respectively. Some of these reactions proceed via the ring-opened ketene tautomer of 348 (240). 

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