1.2- Dithiolane derivatives

Hussain and Nizamuddin have synthesized 1, 3-dithiolane substituted spiro-(5-lactams (Scheme 27) since 1, 3-dithiolane derivatives exhibit various biological activities like fungicidal, bactericidal, and insecticidal [97]. The starting thiadia-zoles 104 were treated with sodium hydroxide and carbon disulfide to get the corresponding disodium dithiocarbamate 105, which were stirred with 1,2-dichlo-roethane to obtain 106. Cyclocondensation of 106 with chloroacetyl chloride in dry dioxane in the presence of triethylamine gave the spiro-(5-lactams 107. These spiro-(5-lactams were found to exhibit antifungal activity 75-85% at 100-ppm concentration against P. oryzae and F. oxysporum. 

A catalytic amount of hydrobromic acid with an excess of hydrogen peroxide is found to be an effective reagent for the facile regeneration of carbonyl compounds from their 1,3-dithiane and 1,3-dithiolane derivatives.136 Bromide-assisted oxidation of substituted phenols with hydrogen peroxide, catalysed by heterogenous WO42-ions, resulted in the formation of p-quinols and their ethers in almost quantitative yields.137... 

Table 3 Bond Angles (°) of some 1,3-Dithiole and 1,3-Dithiolane Derivatives...

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). 

The 1,3 -dithiolane ring also can be cleaved by alkylative hydrolysis using different reagents (77S357). For example treatment of the 1,3-dithiolane derivative (220) with triethyloxonium tetrafluoroborate followed by hydrolysis with copper(II) sulfate solution and basification gives the ketone (221) in 95% yield (77S357). 

Another method involves the reaction of the bis Bunte salt (280) with acetone in the presence of hydrogen chloride at room temperature which proceeds with formation of the 1,3-dithiolane derivative (281) (66HC(21-1)447). The syntheses of several substituted 1,3-dithiolanes have been described (66HC(21-1)447). 

Reaction of the 1,3-dithiolane derived from propiophenone with the reagent hexafluoro-propene-diethylamine and 1,3-dibromo-5.5-dimcthylhydantoin (DBH) yields the vinylic fluoride instead of the expected gem-difluoroalkane (see Section 1.1.7.2.). "... 

The reaction of 1,3-dithiolanes derived from diaryl ketones with sulfuryl chloride and hydrogen fluoride/pyridine as a convenient hydrogen fluoride source gives diaryldifluo-rodiphenylmethanes 9 in high yields. The method is not suited to 2,2-dialkyl- or 2-alkyl-2-aryl-1,3-dithiolancs as chlorination of the substrate occurs. The reaction proceeds equally well with sulfuryl chloride fluoride as a Cl source. 

Dithiolanes derived from chromanones do not form the ew-difluoro compounds, instead they undergo l,3-dithiolane-dihydro-1,4-dithiin rearrangement giving 10. ... 

The 1,3-dithiolane derived from tctralone yields 2-bromo-l.l-difluoro-l,2,3,4-tetrahydronaph-thalene (11), ... 

Table 7 Melting points of selected 1,3-dithiolane derivatives...

Alkylated 1,3-dithiolane derivatives 331 with formyl or ester groups at C-2 could be prepared starting from the unprotected aldehyde 329 or ester 330 (no yields given) (Equation 36) <2000TL5653>. 

An interesting transformation was observed in the case of the 1,3-dithiolane derivative 332, which after deprotonation with LDA smoothly produced the thiolothionophthalic anhydride 335. The proposed mechanism assumed a loss of ethene and intermolecular attack of the resulting intermediate dithiocarboxylate 334 onto the ester function. Further heating of 335 afforded the 3,3 -bithiophthalide 336 in 83% yield (Scheme 43) <20000L3891>. 

Highly enantioselective sulfoxidation was observed using the di-/t-oxo Ti(salen)/UHP (salen = A. A -bisisalicylal-dehydolethylenediamine UHP = urea hydrogen peroxide) catalyst complex in methanol (Equation 43). In oxidations of 1,3-dithiolane derivatives, enantioselectivity increased with the size of the 2-substituent <2002TL3259>. 

Functionalization of the (3-position in the 1,3-dithiolane derivatives 475 was achieved via lithiation with LDA or lithium 2,2,6,6-tetramethylpiperidide (LTMP). The resulting (3-lithio derivatives were trapped with various electrophiles to form the corresponding (3-functionalized 1,3-dithiolanes 476 in 55-96% yields (Equation 57) <1998JOC6239, 1999PS689>. 

Another modification of a cyclopentene moiety was achieved by the cycloaddition reaction of the 1,3-dithiolane derivative 483 with singlet oxygen O2 to form the endoperoxide 484, which upon treatment with either triethyl-amine, triphenylphosphine, or bromine gave the corresponding hydroxy ketone 485, a mixture of the epoxide 486 and the enonc 487, or a mixture of isomeric adducts 488 and 489, respectively (Scheme 69) <1995JOC1333>. 

One of the effective reagents for highly chemoselective dithioacetalization of carbonyl compounds is ceric ammonium nitrate (CAN) in chloroform. When a mixture of benzaldehyde and acetophenone was allowed to react with 1,2-ethanedithiol and a catalytic amount of CAN, the 1,3-dithiolane derived from the aldehyde was obtained in 84% yield while the ketone was recovered unchanged. It is noteworthy that aromatic ketones, 7-lactones, and acylic ketones did not react at all under these conditions and even at elevated temperatures for longer reaction times <1995T7823>. 

Tetracyanoethylene (TCNE) is widely used as an excellent dipolarophile in cycloaddition reactions, also including syntheses of 1,3-dithiolane derivatives. Thus, the reaction of the allylic dithioesters 583 with TCNE produced the 1,3-dithiolane cation radical 584, which next reacted with TCNE yielding 3,3,4,4-tetracyano-5-phenyl-6,8-dithia-bicyclo[3.2.1]octane 585 (Scheme 83) <1995T11503>. 

Ketene itself reacts with l,2-dithiole-3-thiones with formation of a 1,3-dithiolane derivative.211,212 In the same manner a l,2-dithiol-3-one gives a 1,3-oxathiolane derivative (147). 

Dimethylketene reacts in the same way and gives 148, whereas methyl-ketene gives the enolester (149).212 The reaction of diphenylketene with 1,2-dithiole-3-thiones occurs with loss of the thiocarbonyl sulfur213 (e.g., 150). It is suggested that this reaction proceeds via the normal 1,3-dithiolane derivative.211... 

It is of interest to note that tetrathiafulvalene (5) is not planar, but rather slightly distorted into a chair conformation <71CC889>. Also, the five-membered ring of the 1,3-dithiolane derivative (6) was found to be slightly puckered with C(4) and C(5) being above and below the plane defined by S(l>—C(2)—S(3) <54ACS1145>. 

Table 2 Bond lengths (A) of some 1,3-dithiole and 1,3-dithiolane derivatives.

TSA under solvent-free conditions to afford 1,3-dithiane and 1,3-dithiolane derivatives (Scheme 3.14). TSA is a strong solid acid that can activate the carbonyl group to decrease the energy of the transition state of the nucleophilic attack step (Karami et al., 2012i). 

Karami, B., Taei, M., Khodabakhshi, S. and Jamshidi, M. 2012i. Synthesis of 1,3-dithiane and 1,3-dithiolane derivatives by tungstate sulfuric acid (TSA) Recyclable and green catalyst. J. Sulfur Chem. 33(l) 65-74. 

Olefins reacted with 5-phenyl-l,2,4-dithiazole-3-thiones when irradiated to give 1,3-dithiolan derivatives, cyclohexene for example giving (150), which on acid hydrolysis unexpectedly gave (151). The m-fusion of the rings in (151) was established by its conversion into cyclohexene on treatment with triethyl phosphite. Olefins with electron-withdrawing substituents did not react with 5-phenyl-l,2,4-dithiazole-3-thione, suggesting that free-radical intermediates, and not 1,3-dipolar intermediates, were involved in the initial addition. The hitherto unknown l,3-dithiolan-4-thione system has been synthesized cyclohexane-1,1-dithiol reacted... 

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