Dithiolane oxides, synthesis

Dithiolane oxides, synthesis of 241 Dithiolanes, asymmetric oxidation of 291 Divinyl sulphones, reactions of 642, 1021 Divinyl sulphoxides reactions of 349, 352, 353, 359 synthesis of 240 Donor-acceptor capacities 387... 

Advances in synthesis and research of oligomeric tetrathiafulvalenes 97MI9. Enantioselective oxidation of 1,3-dithiolanes to corresponding S-oxides and S,S-dioxides by designer yeast 99JHC1533. 

The l,3-dithiolane-2-thione (326) was first prepared by the reaction of ethylene dibromide with sodium trithiocarbonate in ethanol (1862LA(123)83>. Presumably the best synthesis of (326) is the reaction of ethylene oxide with carbon disulfide and potassium hydroxide in methanol at room temperature (46JCS1050). 

Dithiolanes are efficiently synthesized by the oxidative cyclization of 1,3-dithiols , as illustrated by the preparation of 1,2-dithiolane 77 in quantitative yield from 1,3-propanethiol 76 by oxidation with iodine in the presence of 2-methyl-2-butene (Scheme 44) <20000L369> and a similar synthesis of the l,2-dithiol-3-one 78 (Scheme 45) <2004TL4307, 2006JME5626>. 

A slight variation of the [3-I-2] cycloaddition approach <1977ICA(25)165> has also been employed for the diastereoselective synthesis of the corresponding anti- and ry -iron-substituted 1,2-dithiolane 1-oxides 243 from 237, as a source of electrophilic disulfur monoxide, and 7] -allyl iron complex 242 (Scheme 39). The method was also tested with cyclopentadienyl iron dicarbonyl crotonyl complex 244 when four diastereomers 245-248 were generated in modest yields (35%) <19980M5534>. 

An efficient approach to the synthesis of l,2-dithiolan-3-one 1-oxide, which is the bioactive moiety of macrolactam-type antiobiotic leinamycin 5, involves the sequence of reactions shown in Scheme 49 <2004TL4307, 2006JME5626>. 

The oxidative dimerization of a,o -dithiols carried out by a large number of oxidizing reagents is a well-known and widely used method for the synthesis of cyclic disulfides. An alternative one-step conversion of the acyclic bisthio-cyanates 297 using TBAF in dry THF at room temperature to form cyclic disulfides in moderate yields, including a limited number of 1,2-dithiolanes 298 (Scheme 54), has been developed <1999TL6489>. The available mechanistic information indicates that the process, induced by so-far-unreported nucleophilic attack by fluoride, tolerates ester and ketal groups, while silyl ethers are cleaved. 

A convenient three-component coupling reaction of Meldrum s acid, acrolein, and thioacetic acid was described <1997TL5785> for the synthesis of 2-(l,2-dithiolan-3-yl)acetic acid 315 (Scheme 58). As shown, diacetylthiolated propyl Meldrum s acid 311 was refluxed in methanol affording ester acid dithioacetate 312, which without purification was transformed upon acid-catalyzed methanolysis into diester 313. The subsequent oxidation step led to ester 314 which afforded the final acid 315 by a hydrolysis-decarboxylation sequence. 

Heating several thietanes with sulfur or selenium yields 1,2-dithiolanes and a 2-selenathiolane, for example, 107 from 19, respectively. The reaction of 108 with sulfur provides a synthesis of thioctic acid. ° A somewhat similar reaction involves heating thietane with aluminum oxide whereby 1,2-dithiolane and hydrogen sulfide are produced, but the dithiolane yield is very low. A photochemical ring-expansion of 99 has been described in Section 11.5.1. ° Treatment of thietane with hexafluoroacetone gives a six-membered cyclic sulfenate. ... 

Cyclic Disulphides and Cyclic Diselenides.—Formation. No fundamentally new methods of synthesis of this class of compounds have been reported in the past two years. For l,2>dithiolan the oxidation of l,3>dithiols remains a favoured method, the use of iodine in the presence of triethylamine leading smoothly to 1,2-dithiolans without attendant polymerization. cis- and tra/ -l,2-Dithiolan-3,5-dicarboxylic acids were prepared from a diastereo-isomeric mixture of dimethyl 2,4-dibromoglutarates by sequential treatment with potassium thioacetate and potassium hydroxide in the presence of iodine,and jyn-2,3-dithiabicyclo[3,2,l]octan-8-ol was formed from 2,6-dibromocyclohexanone by successive treatment with potassium thiocyanate, lithium aluminium hydride, and iodine. The stereoselective formation of the less thermodynamically stable alcohol in this case was attributed partly to the formation of chelates with sulphur-aluminium bonds. 2,2-Dimethyl-l,3-dibromopropane was converted into 4,4-dimethyl-l,2-diselenolan on treatment with potassium selenocyanate at 175 °C, but at 140 °C the product was 3,3-dimethylselenetan. Reductive debenzylation of 2-alkylamino-l,3-bis(benzylthio)propanes with lithium in liquid ammonia and oxidation of the resultant dithiols with air afforded 4-dialkylamino-l,2-dithiolans, whilst treatment of a-bromomethyl-chalcone with sodium hydrosulphide gave, as minor product, trans-3 phenyl-4-benzoyl-l,2-dithiolan. Among the many products of thermal decomposition of /ra/ -2,4-diphenylthietan was l,4,5,7-tetraphenyl-2,3-dithiabicyclo [2,2,2]octane. ... 

Synthesis. First obtained and described by Bennett and Statham in 1931, racemic trans-1,3-dithiolane 1,3-dioxide can be conveniently prepared in a good yield (83%) by m-CPBA oxidation (eq 1) of 1,3-dithiolane in dichloromethane or ether, and with complete stereoselectivity (no meso adduct). 

Single and double alkylation of the 1,3-dithiane S-oxide 104 followed by acid hydrolysis results in ring-contraction to form 1,2-dithiolanes 105 and 106 (13RSCA21911). A new method for synthesis of trithiaazapentalene derivatives has allowed examination of the relative contribution of the... 

Heterocyclic Thiols.—Representative synthetic methods described in the recent literature cover the synthesis of tetrachloropyridine-2-thiol from pentachloro-pyridine A -oxide and thiourea, the synthesis of 2-phenylthiazole-5-thiols from the S -acetyl compounds, and syntheses of 4-phenyl-l,2-dithiolan-3-... 

Cyclic Disulphides.— Most of the syntheses of these types of compounds involved oxidation of the open-chain dithiols. Asparagusic acid, or 1,2-di-thiolan-4-carboxylic acid, a new plant-growth inhibitor, has been isolated from extracts of etiolated asparagus and its structure confirmed by synthesis. Brugeriol and isobrugeriol, trans- and cis-4-hydroxy-l,2-dithiolan... 

Miscellaneous. Racemic ketones have been resolved by condensation with (R,R)- or (S,5)-2,3-butanedithiol, then reduced as above to give resolved deoxy compounds (eq 6). Oxidation of prochiral 1,3-dithiolanes under modified Katsuki-Sharpless conditions yields monosulfoxides of high ee. In peptide synthesis, (1) is frequently used as a cation scavenger during deprotection.Transition metal cations are strongly chelated by (1), as exemplified by demetalation of Cu and Ni metalloporphyiins. ... 

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