Sulfur scheme

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Halide ions may attack 5-substituted thiiranium ions at three sites the sulfur atom (Section 5.06.3.4.5), a ring carbon atom or an 5-alkyl carbon atom. In the highly sterically hindered salt (46) attack occurs only on sulfur (Scheme 62) or the S-methyl group (Scheme 89). The demethylation of (46) by bromide and chloride ion is the only example of attack on the carbon atom of the sulfur substituent in any thiiranium salt (78CC630). Iodide and fluoride ion (the latter in the presence of a crown ether) prefer to attack the sulfur atom of (46). cis-l-Methyl-2,3-di-t-butylthiiranium fluorosulfonate, despite being somewhat hindered, nevertheless is attacked at a ring carbon atom by chloride and bromide ions. The trans isomer could not be prepared its behavior to nucleophiles is therefore unknown (74JA3146). 

The [SaN]" cation was first obtained in low yield in 1978 by the oxidation of S7NH with SbCls. The reaction of in situ generated [SN]" salts with sulfur (Scheme 5.3) or the reduction of the [ClSNSCl] cation with anhydrous tin(II) chloride in SO2 or CH2CI2 can be used to prepare [S2N] salts. The best large scale synthesis involves the reaction of AsFs with a mixture of S4N4 and sulfur in the presence of a trace amount of bromine (as a catalyst) (Eq. 5.10). ... 

Very recently, the first disulfur complexes of a tetracoordinated transition metal PtS2[P(Ar)Me2]2 (Ar=Tbt, Bbt) were synthesized by the reaction of ze-rovalent platinum complexes Pt[P(Ar)Me2]2> generated by treatment of the dichloride complexes PtCl2[P(Ar)Me2]2 with lithium naphthalenide, with elemental sulfur (Scheme 6) [37]. Since the use of excess elemental sulfur also... 

Wachter et al. reported the synthesis of polysulfido complexes of group 5 metals by the reaction of the corresponding trihydrides with elemental sulfur (Scheme 15). The reaction of Cp yNbHs with Ss gives the dinuclear poly-... 

The Jt-facial selectivity was explained by the Cieplak Effect due to back-donation of lone pair electrons on sulfur (Scheme 49). Mansuy and coworkers reported that in situ generated thiophene 1-oxide 99 could be trapped by 1,4-benzoqui-none to afford the corresponding syn attack product [58]. Tashiro and coworkers also reported that in situ generated thiophene 1-oxide derivatives 98,100-103 and... 

A series of diastereomerically pure 5 -0-DMT-nucleoside 3 -0-(2-thio-l,3,2-oxathiaphospholanes) and their oxathiaphospholane ring-substituted analogues 283-294 were isolated in 80-83% yield by column chromatography on silica gel of the appropriate diastereomeric mixtures [the ratio ca 55 45 (31P NMR assay)] obtained from the reaction of 2 - A, IV- dii so p rop y I a m i n o- 1,3,2-oxathiaphospholane 279-281 with 5 - 0 -D M T- n uc I cosides 282a-d in the presence of tetrazole (phosphi-tylation), followed by addition of sulfur (Scheme 67) [105-107]. 

Addition of alcohol occurs on P=N bond of 11,2,3]diazaphospholo[ 1,5-a pyridine (2) and P=C bond of 11,4,2 diazaphospholo[4,5-a Ipyridinc (76) in the presence of sulfur or selenium. In the case of 2, addition is followed by 1,3-H shift and a catalytic amount of the respective alkoxide is required for completion of reaction at room temperature. The reaction of 2 with thiophenol is completed at reflux temperature in the presence of sulfur (Scheme 24) [88],... 

Carmack20 has suggested that thiirenes are intermediates in the classic Willgerodt and Kindler reactions of aldehydes or ketones with amines and sulfur (Scheme 3). 

Scheme 6.186) [347]. The condensation of O-allylic and O-propargylic salicylalde-hydes with a-amino esters was carried out either in the absence of a solvent or - if both components were solids - in a minimal volume of xylene. All reactions performed under microwave conditions rapidly proceeded to completion within a few minutes and typically provided higher yields compared to the corresponding thermal protocols. In the case of intramolecular alkene cycloadditions, mixtures of hexa-hydrochromeno[4,3-b]pyrrole diastereoisomers were obtained, whereas transformations involving alkyne tethers provided chromeno[4,3-b]pyrroles directly after in situ oxidation with elemental sulfur (Scheme 6.186). Independent work by Pospisil and Potacek involved very similar transformations under strictly solvent-free conditions [348]. 

Interestingly, the same authors [13b] have isolated the l,2-dihydro-l,2,4,5-tetra-zine intermediate 21 by condensation of 2-cyanopyridine 20 with hydrazine hydrate in presence of flower of sulfur (Scheme 8.9 b). The reaction time is reduced under the action of microwave irradiation (125 W) protic solvents also promote the transformation. 

The 1,2-cyclic sulfites are readily obtained from anomeric mixtures of 1,2-diols by reaction with sulfinyl diimidazolide as mixtures of exo- and endo-isomers at sulfur (Scheme 4.34) [312-314],... 

Thiophenyl acetates (366 R = Me) and propionates (366 R = Et) react with electrogenerated polysulflde ions S3 in DMF to yield thiocarboxylate ions, thiolate ions, and phenyl tetrasulfanide (367), the last deriving from the reaction of thiolate ions with sulfur (Scheme 48). Smdies of the aminolysis by a set of substimted anilines of Y-aryl dithio-2-thiophenates (368 X = S) and dithio-2-furoates (368 X = O) in acetonitrile have shown that the rate-determining step in these reactions is the departure of the thiophenolate ion from the zwitterionic tetrahedral intermediate T= = (Scheme 49). Experiments with deuteriated anilines yielded k i/IcQ values of 1.7-1.9,... 

Structurally similar seven-membered dihydro-l,2,7-thiadiazepine 69 and l,2,7-thiadiazepan-3,6-dione 70 were obtained by an unexpected dimerization of acetoxime 71 (1997BSB605) and a ring closure of dicarboxamide 72 (1995CC1449). Curiously, the reaction of sulfur monochloride containing two sulfur atoms in both cases led to the insertion of one sulfur atom to the seven-membered ling or three sulfur atoms to the by-product 73 in the second reaction, but not two sulfurs (Scheme 36). 

Direct metalation at the /8-carbon of azoles can also occur, although it is a much less facile process than that for the adjacent a-carbon, because of the greater charge density at what is normally a nucleophilic center in enamine-type reactions. Thus in order for reaction to occur, it is usually necessary to either block the a-position or activate the /3-site. If both factors are accommodated than /8-metalation occurs readily, and thus 3,4-disubstituted-2(3//)-thiazolethiones undergo direct lithiation with lithium diisopropylamide (LDA) at the 5-position, which is activated by the inductive effect of the adjacent sulfur (Scheme 4) (80S800). 

The 1,2,3-thiadiazole salt (22) when heated in pyridine affords a reactive intermediate that dimerizes with the extrusion of sulfur (Scheme 4) <86JPR741>. 

The corresponding 1,2-dithiin derivative with bicyclo[2.2.2]oct-7-ene units 213 was synthesized from the diiodide in 59% yield by treatment with 4equiv of ///t-butyllithium in THE at —78°C and subsequent treatment with a toluene solution of an excess amount of elemental sulfur (Scheme 58) <2002JA15038>. The two 1,2-dithiin derivatives 25 and 213 were so stable that decomposition or sulfur extmsion was not observed in daylight and at room temperature in sharp contrast to the light-sensitive nature of other 1,2-dithiin dervatives. 

Reaction of Meldrum s acid derivative 25 with secondary alkylamines in dichloromethane at room temperature afforded a mixture of compounds, including furo[2,3- -l,2,3-dithiazoles 26, the novel Meldmm s acid derivatives 79a-g, and sulfur (Scheme 8 and Table 1). Usually the reaction time is less than 6h with yields of approximately 20%. Of note is the fact that cyclic amines such as piperidine and pyrrolidine do not produce furo[2,3- / -l,2,3-dithiazoles in this way <2000J(P1)3107>. 

Thermal extrusion of a sulfur atom is the most common thermal reaction of a thiepin. The mechanism of this thermal process involves two orbital symmetry controlled reactions (69CC1167). The initial concerted step involving a reversible disrotatory electrocyclic rearrangement is followed by a concerted cheleotropic elimination of sulfur (Scheme 29). Similar aromatization reactions occur with thiepin 1-oxides and thiepin 1,1-dioxides, accompanied by the extrusion of sulfur monoxide and sulfur dioxide respectively. Since only a summary of the major factors influencing the thermal stability of thiepins was given in Section... 

Traditional routes to phenoxazines include the thermolysis of 2-aminophenol and catechol, the latter acting as an acid catalyst, or catechol and ammonia. Phenothiazines are prepared similarly by heating diphenylamines with sulfur (Scheme 10) (B-78MI22701). 2-Hydroxy- (or mercapto-) 2, 4 -dini-trodiphenylamines cyclize to phenoxazines (or phenothiazines) in base by elimination of nitrous acid. This reaction is complicated by Smiles-type rearrangement so that mixtures of isomeric products are obtained (Scheme 11). 

The delay period exhibited with sulfenamide cures is explained in terms of the formation of intermediates by reaction with activated sulfur (Scheme 5) (80MI11508). The 2-mercap-tobenzothiazole (31) produced reacts rapidly with the sulfenamide providing a more facile pathway for vulcanization (equation 11). The amine (38) produced also acts as a catalyst, so that the cure, once started, becomes autocatalytic (64MI11503). 

Though silacyclopropanes readily insert sulfur (Scheme 8), silacyclobutanes are not reported to react. Insertion does occur in the germacyclobutane ring on heating, however, to give the germatetrahydrothiophene. Selenium behaves similarly (Scheme 78) (68JOMI 12)143). 

The C-thioacylation of l-alkyl-2-methyltetrahydropyrimidines and 1,2-dimethyl-dihydroimidazole has been achieved by reaction with thiophene-2-carbaldehydes in the presence of sulfur (Scheme 115) (82T1673). The yield of product is better with thiophene-2-carbaldehydes (30-40%) than with benzaldehyde. 

Azide, sulfonium ylides and (V-aminopyridinium ylides are also known to add to the 2-position of substituted thiopyrylium compounds (presumably via reversible addi-tion/elimination sequences, as for methoxide) and cause ring opening followed by ring closure with loss of sulfur. Scheme 24 shows these conversions (80NKK604). 

Traditional routes to phenoxazines include the thermolysis of 2-aminophenol and catechol, the latter acting as an acid catalyst, or catechol and ammonia. Phenothiazines are prepared similarly by heating diphenylamines with sulfur (Scheme 111). 

Several substituted cyclopentadienylcobalt dithiolenes were obtained57 by a rather surprising route from CpCo carbyne clusters and elemental sulfur (Scheme 3). An astonishing solid state phenomenon was discovered58 in the related CpCo benzenedithiolate a dimerization reaction was observed at room temperature, which could be reversed at 150°C (Scheme 4, see also Section 16.5.3.1). 

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