Dithiolactone

An interesting variation on the Paal thiophene synthesis is observed when applied to an a,p-unsaturated 7-dialdehyde. Thus, treatment of o-phthaldehyde with Lawesson s reagent produced the dithiolactone 36. When 2,3-napthalenedicarboxaldehyde reacted under similar conditions, dithio-2,3-naphthalide 37 was produced in excellent yield. ... 

This 1,3-migration of hydrogen was also observed when 40 reacted with Lawesson s reagent to produce the dithiolactone 41. However, when y-hydroxy-a,P-unsaturated aldehyde 42 was reacted under similar conditions, thiophene 43 was prepared efficiently. These results are not surprising considering that the oxidation state of 42 is equivalent to the traditional saturated 1,4-dicarbonyl substrates of the Paal thiophene reaction via tautomerization of the double bond, and aromaticity is reestablished in the fully conjugated 43. 

Scheme 5. Bridging macrocycles to form bicycles the first successful experiments with bis(thiolactone) 24. The terms bis(thiolactone) and dithiolactone are used in this chapter to describe compounds of type 24 even though such systems are sometimes referred to as dithionolactones or dithioxolactones.

It has been shown that Lewis acid catalyzed isomerization of thionolactones provides access to thiolactones. For example, exposure of the substrate 22 to catalytic amounts of BF3 OEt2 led to efficient conversion to the thiolactone 23. Such transformations were also found to give minor amounts of lactone or dithiolactone side products <06TL6067>. Substituted tetrahydrothiophene derivatives have also been obtained from 1,4-dithiane-2,5-diol and 2-nitroethyl acetate derivatives by a base induced sequence featuring a Michael addition and a Henry reaction <06TL8087>. 

The aldol reaction of dithioester enethiolates has been used for the synthesis of dithiolactones [123], chiral substrates for the Claisen rearrangement [124, 125], and oxathianes [126]. Thioamide enethiolates may be employed in this reaction as well as shown with /Tthiolactams [26], or with a precursor of the antitumour agent vinblastine [127]. 

Particular interest has been shown this year in the photochemistry of thiocarbonyl-containing compounds. Photochemically induced a-cleavage from the lowest triplet state appears to be a general but inefficient reaction of cyclobutanethiones. The biradical intermediate (237) derived from the dithione (238), for example, undergoes closure to the dithiolactone (239) or ring expansion to the carbene (240) which is then trapped with methanol as the... 

An attempted synthesis of thiete by thermolysis (300°) of a Diels-Alder adduct with anthracene was unsuccessful, no doubt because of the thermal instability of thiete.Thiete derivative 215 was obtained by other methods, and structure 217 was suggested as an intermediate in the desulfurization of 216. The unusual dithiolactone 218b is formally derived from a cycloaddition of carbon disulfide with acetylene 218a. " A 2-substituted-3,4-diphenyl-2H-thiete is obtained by treatment of the ylide, 8-methyl-1,3-diphenyldibenzo [e, h]-8-thiazulene, with diphenylcyclo-propenethione. 2-Methoxy-3,4-diphenyl-2H-thiete is one of several products obtained on photolysis of diphenylcyclopropenethione in methanol. ... 

A number of 2-iminothietanes have been prepared from ketenimines and thio-benzophenone ° or thioxanthone. Addition of carbon oxysulfide or carbon disulfide to the phosphonium ylide of a ketenimine 312 gives an imino- 3-dithiolactone as previously noted.Arylsulfonylisothiocyanates undergo cycloaddition at 50°C to vinyl ethers to give 2-iminosulfonylthietanes in 50-76% yields.A ( 2g -I- 2 ) process involving zwitterions was suggested on the basis of the observed stereochemistry. 

H) containing symmetrically bridging thioacyl and thioalkyl functions are obtained with molybdenum as the central metal (46). The dithiolactone S= C(CH2)2CH2S reacts similarly with the molybdenum complex, but in the product the a carbon is link to the nonadjacent sulfur atom by an alkyl chain (47). 

Unlike the ruthenium alkynyl complex in Table III, the iron complex 328 does not undergo insertion with CS2, but forms a [2 + 2] cycloaddition product (329) containing a 2//-thiete-2-thione 08-dithiolactone) functional group, which can react further with electrophiles, for example, Mel. The CS2 addition was found to be reversible in solution and in the solid... 

In a heterocyclic environment, the dithiocarboxylate functionality may give a more complex reaction pattern, as shown by dithiolactones (19). Here, secondary aliphatic amines lead to ring cleavage providing 2-(thioacylamino)thiobenzamides (20), whereas primary aliphatic or aromatic amines give thiolac-tams (21 Scheme 5). ... 

Allenylsilveifl) compounds are prepared in situ by deprotonation of the allenic hydrocarbon with n-butyllithium and subsequent treatment with silver bromide (equation 5). Allenylsilver compounds afford allenic derivatives when treated with a variety of electrophiles, without significant isomerization to the propargyl system (equation Reaction of the allenylsilver compound with carbon disulfide results in an interesting transformation to p, y-unsaturated-7-dithiolactones presumably by way of silver salts (Scheme 11). - ... 

Oxidation. MCPBA is useful for oxidation of a-dithiolactones to give 1,2-dithietan-... 

Muthuramu and Ramamurthy have reported the first example of Norrish Type 1 cleavage in a thione, or more specifically a dithiolactone. 

A spirocyclic dithiolactone 65 was synthesized in high yield by sulfenyl group-assisted dehydration followed by intramolecular cyclization of P-hydroxy y-(phenylthio) dithioate66 (Scheme 16) [52,53]. 

The synthesis of the five-membered cyclic dithioate 65 is shown in Scheme 16 [52,53]. The parent y-dithiolactone (3,4,5-trihydrothiophene-2-thione) (146) is prepared by thionation of the corresponding thiolactone 147, as shown in Eq. 32 [74]. Preparations for the l,3-dithiolane-4-thione derivatives 148 have been reported [75,76] (Scheme 32). It was proposed that the adamantanespiro compound 148a was formed by a reaction of the thiocarbonyl ylide, generated from 149 by extrusion of N2, with carbon disulfide [75]. 

The reaction of diiodide with phosphorus pentasulhde instead of sulfur gives dithiolactone 162. " ... 

Treatment of 57 with 1.2equiv of sodium thiophenolate in refluxing acetone afforded a 44% yield of the dithiolactone 155 (Equation 11) <1997LA1517>. 

Alkyl- and aryl-substituted 2,5-dihydroxythieno[3,2-Zi]thiophenes appeared to occur exclusively as dithiolactones. In no case was the hydroxy form of these compounds detected (78JOC2197). NMR spectroscopy demonstrated that 2,3-dihydrothieno[3,2-Zi]thiophene-2,5-dione (E) is a favourable structure. Tautomer F was detected only for the unsubstituted compound. However, this tautomer is readily transformed into tautomer E. For 6-substituted compounds, two stereoisomers of the form G are observed these stereoisomers have opposite configurations at the C(6) atom. 

The reaction is completed within 5-15 min if tetralin at 210 °C is used as solvent. Also, dithio-y-lactones, including dithio-phthalides and dithio-Q -p)Tones, are formed smoothly whereas the hitherto unknown simple or 3-dithiolactones cannot be prepared, neither with LR nor by any other method. Interestingly, dithiopilocarpine is formed as a mixture of diastereomers on reaction of pilocarpine with LR (eq 16), i.e. both oxygen atoms of (12) are replaced by sulfur. In an interesting sequence of thion-ation and rearrangement reactions, three different thiono analogs of 1,8-naphthalic anhydride were prepared (eq 17). ... 

Miscellaneous Reactions of LR. Under particular conditions, certain carbonyl compounds and other substrates react with LR to form thiophosphonates or heterocycles, which fact throws some hght on the mechanism of thionation reactions with LR. Carbinols undergo nucleophilic substitution with LR to form the corresponding thiols. The redox properties of LR can be utilized to prepare dithiolactones from dialdehydes (eq 22), a-0X0 thioamides from nitro ketones (eq 23), or sulfides from sulfoxides. ... 

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