1.3- Dithiolanes reduction

The formation of S-oxides has also been observed when oxidizing a variety of 5-substituted 2-tert-butyl-l,3-dithianes in wet acetonitrile. In an undivided cell, 4-substituted 1,2-dithiolane-l-oxides were oblained (Scheme 25) [113]. A coupled cathodic process, in this case, was the reduction of protons formed in the anodic reaction. 

Reductive cleavage of 1,3-dithiolanes is accomplished in low yields with sodium in liquid ammonia and gives either dithiols or mercapto sulfides depending on substituents in position two [679]. 

Scheme 1.64). The Ag(I)-mediated cyclization afforded dipole 306 for 1,3-dipolar cycloaddition with methyl vinyl ketone to yield adducts 307 and the C(2) epimer as a 1 1 mixture (48%). Hydrogenolytic N—O cleavage and simultaneous intramolecular reductive amination of the pendant ketone of the former dipolarophile afforded a mixture of alcohol 308 and the C(6) epimer. Oxidation to a single ketone was followed by carbonyl removal by conversion to the dithiolane and desulfurization with Raney nickel to afford the target compound 305 (299). By this methodology, a seven-membered nitrone (309) was prepared for a dipolar cycloaddition reaction with Al-methyl maleimide or styrene (301). 

The reaction of a 1,3-dithiolane (336) with n-butyllithium has been shown to result in fragmentation to the corresponding thiocarbonyl compound via the mechanism detailed in Scheme 73 (80JA3S77). The thiocarbonyl compound can react further with excess lithium reagent to provide the product of carbon addition (aldehyde precursors) or reduction (saturated ketones). 

Dithioacetals (see also dithianes and dithiolanes) alkylation of 98 as acyl anion equivalents 75 carbanions of 87,97-102 cleavage of 14-18,98,102 desulfurization of 78 metal-catalysed coupling 127 reaction with Grignard reagents 127 reductive lithiation of 89 synthesis of 12-19,97-102 Dithioacids synthesis of 40... 

Dithiolanes are quite resistant to both alkaline and acid hydrolysis, however the ring can be cleaved by cadmium carbonate and mercury(II) chloride, a well-known reagent for hydrolyzing thioacetals (53MI43200). Thus the 1,3-dithiolane derivative (218) is hydrolyzed by this reagent with formation of the hydroxydithiol (219). A similar reaction takes place on reduction of the 1,3-dithiolane derivative (218) with sodium and ethanol in liquid ammonia to produce the hydroxydithiol (219) (47JCS592). 

C2-symmetric cyclic alkenyl sulfoxide (187), with cyclopentadiene, proceeded under mild conditions to give a single diastereomeric adduct (188) in excellent yield (Scheme 48). Other acyclic dienes also gave single diastereomeric adducts often without the necessity of using Lewis acids. The Ws-sulfoxide moiety can be readily deprotected using a two-step sequence of sulfoxide reduction followed by hydrolysis of the dithiolane to give the enantiomerically pure norbomenone (189). 

Thioxanes (60) give similar ring-opening reactions but the subsequent reaction to lose oxygen is not observed.1,3-Dithiolanes such as the cis and trans forms of (61) can be isomerized by Lewis acids but fail to undergo reduction with H2AICI this may be a consequence of solubility problems. 

C—S bonds can be cleaved reductively by dissolving metals, by processes which depend on the ability of sulfur to accept electrons.1,3-Dithiolanes tend strongly to suffer cleavage of both C—S bonds with sodium in liquid ammonia when C-2 is unsubstituted or carries a phenyl group isopropylidene derivatives (70), however, give single cleavage (equation 39). Bond rupture requires formation of a relatively stable carbanion. 

Sodium borohydride reduces disulfides to thiols, which can then be used to reduce nitro groups. Based on the redox properties of 1,2-dithiolane, lipoamide (17) was used for the selective reduction of mono-substituted nitrobenzenes to the corresponding anilines. Lipoamide (17) can also be immobilized on hydrophilic polymers such as polyvinylamine, polyethyleneimine and chitosan. These polymeric reducing catalysts can be recycled and are easy to separate from the reaction mixture. The system has been used to reduce nitroarenes to anilines. ... 

Dithiolanes, also named five-membered 1,3-dithioacetals or A,3 -acetals, find wide applications in organic synthesis, particularly in protection of carbonyl functions and their reductive conversion to hydrocarbons or olefins. Due to the stability of 1,3-dithiolanes toward various reagents and reaction conditions, they have attained an important position in this area despite the fact that dedithioacetalization to the corresponding carbonyl compounds is sometimes not an easy process. There are three general strategies that can be used for deprotection of 1,3-dithiolanes involving... 

Aryl-substituted 1,3-dithiolanes were useful substrates for the preparation of vinylsilanes. Treatment of 2-phenyl-substituted 1,3-dithiolanes 274 with Me2(t -PrO)SiCH2MgCl in the presence of a Ni-catalyst afforded the vinylsilane 275 in 85% yield. Subsequent reduction of the Si-O bond with LiAlH4 led to the formation of 276 in 75% yield (Scheme 34) <1997JA11321, 1998T1197>. 

A selective reduction of the carboethoxy group in the 1,3-dithiolane 490 with NaBH4 in ethanol or in a mixture of ether/MeOH provided the alcohol 491 in quantitative yield (Equation 58). A selective reduction of the ester group to formyl was also possible <2000TL5653>. 

The first thiete fused to an aromatic system 219 (and an anthracene derivative) was reported in 1965 and was prepared by reduction of a naphthothiete sulfone. An attempt to prepare benzothiete by desulfurization of benzo-l,2-dithiolane was unsuccessful. Photolysis of benzo-l,2-dithiolane 1,1-dioxide in an attempt to extrude sulfur dioxide to give benzothiete also was unsuccessful. The naphthothiete 205, however, was prepared by extrusion of sulfur dioxide from 220 and nitrogen from 221. Thiete 205 also is obtained in 6-8% yield by treatment of 1,8-dehydronaphthalene with carbon disulfide. The unstable thiolactone 211 was formed by a photochemical extrusion of benzaldehyde from 222 and from 222a at 350°C. The benzothietes 209, 223, " and 224 have been... 

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

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