Thiolate addition

In a thorough investigation of thiolate additions to acceptor-substituted enynes, Shus-trova and coworkers180,181 were able to demonstrate that the ratio of 1,4- and 1,6-addition depends on the reaction conditions, in particular on the duration of the experiment (equation 75) whereas only 1,4-adduct was observed in the reaction of methyl 6,6-dimethyl-2-hepten-4-ynoate and ethyl thiolate after 1 h, the product distribution shifted towards the 1,6-addition product with increasing reaction time, the latter being the sole... 

In the initially proposed mechanism, the intermediate 2-nitro-2-propyl radicals, Me2(N02)C, undergo two reactions with the more basic (nucleophilic) thiolates addition of thiolates leading to SRN1 products (Equation 10.20 in Scheme 10.32), and SET to yield the nitro anion and thiyl radicals (RS ), Equation 10.21, which combine to give disulfide. 

Thiolate addition is a simple reaction and once we had realized the necessity of including explicit solvation was straightforward this work will be reported shortly. 

Magnus, P. Eisenbeis, S.A. Rose, W.C. Zein, N. Solomon, W. Studies on dynemicin. A nonradical cycloaromatization pathway for the azabicyclo [7.3.1]enediyne core structure initiated by thiolate addition. J. Am. Chem. Soc. 1993, 775, 12627-12628. 

CHaSNa, DMF, -20°C, 1-7 h, 77-91% yield or 25°C, 4 min, 86% yield. In this case, cleavage occurs by thiolate addition to the 10-position followed by elimination. 

The first step of this process involves the Knoevenagel condensation of an aldehyde with malononitrile to form the corresponding Knoevenagel product (5). The second molecule of malononitrile then undergoes Michael addition to 5 followed by simultaneous thiolate addition to C N of the adduct and cyclization to dihydropyridine (6) which on aromatization and oxidation (air) under the reaction conditions leads to pyridine. 

This enhanced reactivity difference for thiolate addition has been attributed to the combination of two factors. The first is the favorable soft acid-soft base interaction for the reaction of the soft carbene complex with the soft thiolate ion which contrasts with the unfavorable hard acid (CH3COH)-soft base (EtS ) interaction in reaction (66). The second is the favorable hard acid-hard base interaction between the hard MeO with the hard methylbenzoate which contrasts with the unfavorable soft acid-hard base interaction in the reaction of the carbene complex with MeO. ... 

Aminothiazole derivatives (243) can be prepared by treatment of enamines of type 240 with sulfur and cyanamide at room temperature in ethanol (701) yields range from 30 to 70%, and no catalyst is required. Initial formation of the thiolated intermediate (241) is probably followed by addition of cyanamide, yielding 242 (Scheme 124). 

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). 

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

Chemisorption of alkanethiols as well as of di- -alkyl disulfides on clean gold gives indistinguishable monolayers (251) probably forming the Au(l) thiolate species. A simple oxidative addition of the S—S bond to the gold surface is possibly the mechanism in the formation of SAMs from disulfides ... 

The 3-substituents in 3-nitro- and 3-phenylsulfonyl-2-isoxazolines were displaced by a variety of nucleophiles including thiolate, cyanide and azide ions, ammonia, hydride ions and alkoxides. The reaction is pictured as an addition-elimination sequence (Scheme 54) (72MI41605, 79JA1319, 78JOC2020). 

A thiol, usually under basic catalysis, can undergo Michael addition to an activated double bond, resulting in protection of the sulfhydryl group as a substituted S-ethyl derivative. Displacement of an ethyl tosylate by thiolate also affords an S-ethyl derivative. 

Quite a number of asymmetric thiol conjugate addition reactions are known [84], but previous examples of enantioselective thiol conjugate additions were based on the activation of thiol nucleophiles by use of chiral base catalysts such as amino alcohols [85], the lithium thiolate complex of amino bisether [86], and a lanthanide tris(binaphthoxide) [87]. No examples have been reported for the enantioselective thiol conjugate additions through the activation of acceptors by the aid of chiral Lewis acid catalysts. We therefore focussed on the potential of J ,J -DBFOX/ Ph aqua complex catalysts as highly tolerant chiral Lewis acid catalyst in thiol conjugate addition reactions. 

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... 

Similarly, when aziridines 16 were opened with thiolates, exclusive addition at the carbon proximal to the carbonyl was observed (Scheme 12.21). The best results were obtained when DMF was used as the solvent. 

Like gold, silver readily forms insoluble (yellow) thiolates [Ag(SR)] primary alkylthiolates are thought to have non-molecular structures but with bulky tertiary alkyls (n = 8), probably having a cyclic structure. Addition of excess thiolate leads to the formation of clusters like Ag6(SPh)g, Ag5(SPh)7 and Ag5(SBu )6 (phosphine adducts are known, too). 

The experiments with 2-(3-butenyloxy)benzenediazonium ions (10.55, Z = 0, n = 2, R=H) and benzenethiolate showed a significant shift of the product ratio in favor of the uncyclized product 10.57. They also indicated that the covalent adduct Ar — N2 — SC6H5 is formed as an intermediate, which then undergoes homolytic dissociation to produce the aryl radical (Scheme 10-83). Following the bimolecular addition of the aryl radical to a thiolate ion (Scheme 10-84), the chain propagation reaction (Scheme 10-85) yielding the arylphenylsulfide is in competition with an alternative route leading to the uncyclized product 10.57. 

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