Sulfur transfer

Tliiobenzophenone 5-sulfide (35) was successfully generated by a cycloreversion of the 1,2,4-trithiolane 36 at 60°C or by a sulfur transfer from thiiranes to tliiobenzophenone (87JA902 97T939).Tlie thioketone 5-sulfide... 

Dithiatopazine 73 serves as a sulfur-transfer reagent under thermal conditions. Tlius, heating 73 and diene 130 in toluene at 100°C formed a cyclic disulfide 131 (25%) and a tetrasulfide 132 (28%) with the formation of the alkene 118 (90%). Under similar conditions, the highly strained acetylene 133 was converted to the 1,2-dithiete 134 (65%) and the congested thiophene 135 (12%) (90JA3029). 

The ion-molecule reaction between thiirane and its radical cation to form a thiirane sulfide radical cation and ethylene has been studied by Qin, Meng and WiUiams [134]. ESR studies using a low-temperature sohd-state Freon radiolysis technique provided compeUing evidence that the hemibonded dimer radical cation of thiirane is an intermediate in this so-called sulfur-transfer reaction see Scheme 2. 

An analogous sulfur transfer reaction has been proposed for the thermal decomposition of neutral thiirane to give ethylene and elemental sulfur, on the basis of ah initio calculations at the G3(MP2) level of theory [135]. 

Cp = Ti -CgHs R = 4-CIC6H4 dppe = (Ph2PCH2)2 TTP = meso-tetra-p-tolylporphyrinato Scheme 47 Sulfur transfer reactions by the use of TiCp2Ss... 

Scheme 49 Sulfur transfer reactions by the use of TiCp2(S6C6Hio) and TiCp2Sg...

It has been reported that the zinc hexasulfido complex, Zn(S6)(TMEDA) (TMEDA=] r,] T,N, N -tetramethylethylenediamine) acts as a sulfur transfer reagent in an analogous manner as the above-mentioned titanium polysulfido complexes. The sulfur transfer reaction between Zn(S6)(TMEDA) and TiCp2Cl2 cleanly proceeds at room temperature to afford ZnCl2(TMEDA) and TiCp2S5 together with Ss (Scheme 51) [132]. This result suggests that... 

The bisazolylsulfides shown below are much better sulfur transfer reagents than SXC 2 (x — 1, 2). Moreover they are reactive toward alcohols and primary and secondary amines. 

From X-ray crystal structures of the products, the reactions of these stereoisomeric disilenes with episulfides, and with sulfur, were shown to proceed with retention of configuration at silicon. These findings suggest that the reaction proceeds in a concerted fashion, through intermediates or transition states involving tetracoordination for the sulfur atom being transferred (Scheme 13). Similar intermediates are believed to occur in other sulfur-transfer reactions.86... 

If ammonium thiocyanate is used, the ammonium ion can itself provide a nitrogen atom for heterocyclic ring construction. Such nitrogen and sulfur transfer is the basis of an elegant synthesis of isothiazoles (15) from 3-chloropropenals (16).18... 

Thionyl chloride (SOCl2) is the most versatile of all sulfur transfer reagents in heterocyclic synthesis. The sulfur-oxygen bond renders the sulfur atom more electrophilic the possibility of ready removal by elimination of the oxygen atom allows easy aromatization of many of the initially formed sulfur heterocycles. Two general reviews of the chemistry of thionyl chloride are available.53 Both cover the literature up to about 1970. 

Compounds containing the iV-thiosulfinylamino group (R—N=S=S) have been reported recently.85 "88 The aryl compounds are rather unstable purple oils which show promise as sulfur transfer agents, although few definitive examples have yet been reported.87... 

The use of other phosphorus-sulfur reagents for heterocyclic synthesis appears rare. It would be interesting to investigate in more detail the reaction of compounds, such as the phosphine sulfides, with organic substrates. Triphenylphosphine sulfide is an effective sulfur transfer agent, as it converts oxiranes into thiiranes in good yield. The reaction proceeds with retention of configuration.128... 

The remaining four chapters of the present volume involve topics new to the series. Two of them deal with specific groups of compounds (C. J. Moody on Azodicarbonyl Compounds and T. Sasaki on Heteroada-mantanes ) and two others deal with the Use of Transition Organome-tallic Compounds in Heterocyclic Synthesis (J. L. Davidson and P. N. Preston) and Sulfur Transfer Reagents (M. Davis). 

The oxygen of azole A-ox ides produces a nucleophilic attack to C=S C-atom of a cycloalkanethione forming a zwitterion, which cyclizes and spontaneously decomposes, yielding the product of this sulfur transfer reaction201 (Scheme 16). 

Benzyltriethylammonium tetrathiomolybdate, [BnNEt3]2MoS4, is a useful sulfur transfer reagent which has now been shown to effect a one-pot, three-step sequence of S-transfer— reduction—Michael addition. The intramolecular version successfully produces 1,4-oxathianes from the bromoenone 108 (Scheme 65). In like manner, the bicyclo[3.3.1]nonane skeleton incorporating a thiopyran ring can be constructed . 

The a,a -dioxothione 109 can be generated from indan-l,2,3-trione using potassium thiotosylate as the sulfur transfer reagent and has been trapped as its [4+2]-cycloadduct 110 (Scheme 66). A 1,3-sulfinate migration from S — O is involved . 

Smith AD, Agar JN, Johnson KA, et al. 2001. Sulfur transfer from IscS to IscU The first step in iron-sulfur cluster biosynthesis. J Am Chem Soc 123 11103-4. 

The absolute rate constants for oxygen and sulfur transfer to a range of carbenes (dialkyl, cycloalkylidene, alkylchloro, diaryl, arylchloro, arylalkoxy, and dialkoxy), generated by laser flash photolysis of diazirine or oxadiazoline precursors, were determined. No evidence was seen for ylide formation and a concerted mechanism via an ylide-like transition state was proposed. 

But these disulfides 1 do not substitute for sulfur monochloiide, and so S2CI2 has ranked among the best sulfur transfer reagents in inorganic and organic chemistry since its discovery in the late 1800s (1860LA266). 

In order to decrease sulfur emissions, sulfur transferring catalysts containing AI2O3 or MgO (11-13), can be used. 

Treatment of 1,2-dihydroxyethane or higher 1,2-diols with S2CI2 <65JOC2696>, or with the sulfur transfer agent, thiobis(benzimidazole) <80CC825>, afforded 1,3,2-dioxathiolane 2-thiones. 

Sulfur transfer can also occur from sulfurated borohydride exchange resin <2001TL6741> the reaction proceeds in methanol at ambient temperature rapidly (<5min) and in high yield (91%). From l,4-di(acetylthio)butane, 1,2-dithiane can be obtained by a one-pot synthesis in excellent yield (98%) using BuzSn(OMe)2, FeCls, and a catalytic amount of CsF as a promoter in THF solution <1990TL3595>. 

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