Of dithiolanes

The preparation of e/n-difluoro compounds by the oxidative fluorodesul-furization ot 1,3-dithiolanes readily proceeds by treatment with a pyridinium polyhydrogen fluoride-Af-halo compound reagent the latter serves as a bromonium ion source [2], l,3-Dibromo-5,5-dimethylhydantoin is the most effective of several At-halo oxidants. It is believed that /V-halo compounds combine with hydrogen fluoride to generate in situ halogen fluorides, the oxidants. Formation of gem-difluorides from dithiolanes derived from ketones is efficient and rapid, even at -78 °C, whereas the reaction of dithiolanes derived from aldehydes requires higher temperature (0 °C) (equation 4). 

Pyridyl-l,3-dithianes (50) result from the reaction of picolyl lithium reagents with 1,2-dithiolanes in the presence of HMPT. An initial ring opening is followed by reaction at the carbanion site with a second mole of dithiolane <96PS(112)101>. 

Di- -butylstannyl dithiolates also serve as sources of dithiolanes and dithianes. These reactions are catalyzed by di-u-butylstannyl triflate.102... 

Comparative Metabolism of Dithiolane Insecticides in Plants, Animals, and the Environment... 

An interesting synthetic approach to thietanes is the selective desulfurization of cyclic disulfides.The treatment of dithiolanes with a diethyl-aminophosphine results in a ring contraction to thietanes, (Eq. 19). This has been demonstrated with a-lipoic acid, a coenzyme with a dithiolane structure involved in the biological oxidation of pyruvic acid. The reaction is proposed to be initiated by the electrophilic attack of the phosphorus on the ring sulfur atom, resulting in the formation of an acyclic internal phosphonium salt, which by subsequent elimination of a phosphine sulfide, closes to the four-membered ring. °... 

New applications for 1,2-dithiole and dithiolane compounds include evaluation of dithiolanes such as 84 and 85 as flavour components <98MI177>, 86 as a new indigo chromophore <99T14429>, 87 as a fungicide and insecticide <99JAP11279179>, 88 as a... 

Pyrolytic methods involve the use of dithiolane S, S -dioxides as starting materials which, upon heating, afford reactive thioaldehydes, such as trifluorothioacetaldehyde, trapped as the Diels-Alder adduct369,370 (equation 82). In equation 80 an enethiolate was formed, and this feature has been employed also in the cleavage of the oxathiolane 78. The silver vinylthiolate 79 thus obtained was applied in the preparation of new antibacterial cephem derivatives371. 

Dithiolane-fused oxadithiepins, widely used in the synthesis of charge-transfer complexes, are available by [3+4] substitution reactions of dithiolane dithiolates with di(chloromethyl) ether (see Section 13.16.9.4.1). 

The intramolecular thia-anti-Michael addition has been reported to occur on treatment of dithiolane (86) with aliphatic primary amines, which produced a series of... 

Fig. 54 Pyridine catalyzed ring-expansion polymerization of dithiolane-2,4-dione...

Though the anion of dithiolane decomposes as described in the chapter and cannot be used as a d1 reagent, the example shown here works well without any decomposition. Explain and comment on the regioselectivity of the reaction. Anions of dithianes are notorious for preferring direct to conjugate addition. 

A base-induced ring opening of dithiolanes 34 and subsequent cyclization gives 5-vinylsulfanylthiophenes 35 (Scheme 8) <2004H(63)1281>. 

In Kiyooka s approach to acetate aldols by use of a stoichiometric amount of 3f, the enantiomeric excess obtained in the reaction with silyl ketene acetals derived from a-unsubstituted acetates was much lower (ca 10-20 %) than that obtained in the reaction with l-ethoxy-2-methyl-l-(trimethylsiloxy)-l-propene (> 98 % ee). Introduction of an removable substituent, e.g., a methylthio or bromo substituent, after aldol reaction at the a-position of chiral esters, resolved this problem [43e], Asymmetric synthesis of dithiolane aldols was achieved in good yield by using the silyl ketene acetal derived from l,3-dithiolane-2-carboxylate in the 3f-promoted aldol reaction, and desulfurization of the dithiolane aldols resulted in production of the acetate aldols in high enantiomeric purity (Eq. 56). 

Another method for the formation of dithiolane derivatives, exploiting the potential of organometallic reagents but limited to two examples, is the nucleophilic ring opening of aziridines 289 and 295 (Scheme 53) with benzyltriethy-lammonium tetrathiomolybdate 290 <2002SL1762, 2005JA12760>. 

Reaction of dithiolane (70) with BuLi followed by a hindered organoborane gives (71), which after oxidative woric-up affords an unsymmetrical ketone in good yield (Scheme 43). ... 

Scheme 4.10 Reductive removal of dithiolane moieties from silicon-containing compounds with calcium reagents...

Kiyooka et al. have reported that stoichiometric use of chiral oxazaborolidines (e.g. (S)-47), derived from sulfonamides of a-amino acids and borane, is highly effective in enantioselective aldol reactions of ketene TMS acetals such as 48 and 49 (Scheme 10.39) [117]. The use of TMS enolate 49 achieves highly enantioselective synthesis of dithiolane aldols, which can be readily converted into acetate aldols without epimerization. The chiral borane 47-promoted aldol reaction proceeds with high levels of reagent-control (Scheme 10.40) [118] - the absolute configuration of a newly formed stereogenic center depends on that of the promoter used and not that of the substrate. 

Syntheses of dithiolanes, dithiolium salts, and tetrathiafulvalenes from carbon disulfide 84S797. 

These derivatives are often difficult to cleave. The following method relies on the essential irreversibility of dithiolane formation. 

Scheme 2.68 Proposed mechanism of oxidative fluorodesulfuration of dithiolanes [142] (X stands for electrophilic bromine Br+ , iodine 1+ , or the nitrosyl cation, NO+).

Also alkynes have been used for the synthesis of dithiolanes. Thus, 2,3-dithioquinoxaline (355) gave, by vinylogous addition onto 3-oxo-l-alkynes (356) 2-(2-oxoalkyl)-l,3-dithiolo[4,5-i]qui-noxalines (357) (Equation (73)) <82KGS1489>. 

When the reaction of TFE and sulfur is carried out in a closed system by continuous addition of TFE to molted sulfur, compound 53 (contaminated by trace of dithiolane 54) can be prepared in 61 % yield. The formation of 54 can be suppressed by using CS2 as a solvent (Fig. 9.13). 

The regioselectivity of dithiolane formation from unsymmetrical 1,4-diketones has been examined [93SUL1S7]. Electrocyclic reaction of allyl dithiobenzoate with TCNE gives bicyclic dithiolane (60) [94SUL119]. Substituent effects on the cycloaddition of dithioesters with alkynes to gives 1,3-dithioles have been investigated [93ZOR1089]. Reaction of aliphatic dithioacid dianions with CS2 followed by electrophiles leads to a variety of 1,3-dithiole... 

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