Sulphoxides pyrolysis

Cycloalkanones are converted into the corresponding a-epoxy-sulphoxide using chloromethyl phenyl sulphoxide. Pyrolysis of the epoxide yields the cycloalkene carbaldehyde (Scheme 52). One-carbon homologation of heptanal to -oct-2-en-l-al was accomplished using the same strategy. ... 

Sulphenyl Halides.—Sulphenyl chlorides are readily available by chlorinolysis of disulphides, and this remains the most commonly used method of synthesis. Chlorinolysis of penicillin esters gives the sulphenyl chloride, and a route to an azetidinone sulphenyl chloride has been devised in which the relatively unstable sulphenic acid produced by penicillin sulphoxide pyrolysis is treated with SOCh in CCl, to give [43 R =C1, R =CH(C02Me)CMe=CH2]. Sulphenyl iodides may be important intermediates in reactions at disulphide bridges in peptides and proteins, and a report of the preparation of a stable sulphenyl iodide is notable. The observation that methanesulphenyl chloride dimerizes (in SO2 in the presence of a Lewis acid) to give MeSSMeCl Cl MeS=SMeCl Cl may be useful in explaining the course of certain electrophilic reactions of sulphenyl chlorides, and should stimulate a search for new reactions of aliphatic compounds of this series. 

In the case of flash vacuum pyrolysis, the reaction may be of some synthetic utility. For example, at 700 °C diphenyl sulphoxide produces diphenyl thiosulphonate in 40% yield, however, several other products are also formed. 

Prostaglandins 624, 725, 960 Prostanoids 620 Protonation 565-567, 1049 photochemical 882 Pseudopotential methods 15, 16 Pummerer rearrangement 240, 243, 470, 843 Pyramidal inversion 602, 604 Pyrazolenines 749 Pyridazine oxides 640 Pyridine aldehydes, synthesis of 310 Pyridine oxides 640 Pyrolysis 102-105 of sulphones 110, 679-682, 962 of sulphoxides 739, 740 Pyrroles 265, 744... 

Photolysis and flash vacuum pyrolysis of diaryl sulphoxides both lead to the formation of thiosulphonates as shown in equation (73). This reaction presumably occurs by initial S—C bond scission followed by combination of two arylsulphinyl radicals as depicted in equation (74). 

The pyrolysis of steroidal sulphoxides also gives olefins. A recent study [144a] using the eight isomeric 3-phenylsuh phinyl- and 4 phenylsulphinyl-5a Cholestanes showed that development of the cyclic transition state e.g. 8) is controlled not only by the availability of a suitable cis hydrogen but also... 

Pyrolysis (in boiling toluene) of the sulphoxide obtained from a dialkyl (l-phenylth> ioalkyl)phosphonate (339) and 3-chloroperoxybenzoic acid affords an alkenephosphonic diester, and subsequent work showed that the sequence was adaptable to the production of chiral esters of alkenylphosphonic diester with optical purities of not less than 93%. Use of the ( S )p-phosphonic amide 340 afforded a mixture of the (E)-(S)p- and (Z)-(S)p-stereoisomers (341), separable by chromatographic methods. ... 

Pyrolysis of aryl sulphoxides gives rise to alkenes. Coupled with Michael addition of nucleophiles to aryl vinyl sulphoxides, a rather general synthesis of substituted alkenes results. Annulenophanes have been prepared by photolytic triethyl phosphite-induced desulphurization of cyclic bis-dialkylsulphides. ... 

Some cycloeliminations use a ring of five atoms instead of six but still involve six electrons. This is no longer a retro ene reaction but it is still a retro group transfer and is allowed in the all-suprafacial mode. Some common examples of such reactions are pyrolysis of amine oxides, sulphoxides, and selenoxides. All these reactions are syn stereospecific. 

On pyrolysis, sulphoxides with a (3-hydrogen undergo syn elimination to give alkenes (Scheme 6.24). The pyrolysis of sulphoxides takes place at about 80 °C. Like other concerted pericyclic reactions, this reaction is also highly stereoselective. For example, the anff-sulphoxide (1) on pyrolysis gives mainly frawi-methylstilbine (2), whereas the corresponding jyn-sulphoxide (3) gives predominantly cw-methylstilbine (4). 

The chirality at sulphur in 3a-t-butylsulphinyl-5a-cholestanes determines the proportions of olefins formed on pyrolysis, while n-butyl isomers with R)- or (5)-chirality at sulphur give the identical product mixture. It would seem that the steric requirements of n-butyl are too small to influence the disposition of groupings that are involved in the transition state leading to elimination products. In addition to cholestenes, the 3a-t-butyl sulphoxides give sulphur-containing steroids, including the disulphide (102). 

The principal component of the lachrymatory factor of the onion (Allium cepa) has been identified by flash vacuum pyrolysis (FVP)/microwave techniques as (Z)-propanethial 5-oxide, CH3CH2CH=S=0. It functions as a 1,3-dipole and as a dipolarophile, and it dimerizes in cold benzene to give principally trans-3,4-diethyl-1,2-dithietan 1,1-dioxide rather than 2,4-diethyl-1,3-dithietan 1,3-dioxide, as previously proposed. Formation of this sulphine from its cellular precursor, rran5-(+)-S-(prop-l-enyi)-L-cysteine sulphoxide, is suggested to involve the formation of a Schiff base and the elimination of ( )-prop-l-enesulphenic acid, which then rearranges to the sulphine (Scheme 2). 

Pyrolysis of N-oxides known as Cope elimination takes place at lower temperatures (100-150 °C). The pyrolysis of sulphoxides and selenoxides takes place easily below 100 °C because of weaker C-S and C-Se bonds. As for example, ery/firo-N-oxide 6 and eryT/iro-sulfoxide 7 on pyrolysis give cis and trans olefins as major product, respectively. 

The standard method for the conversion of a-thio-esters into a,/3-unsaturated esters involves oxidation to the corresponding sulphoxide followed by pyrolysis. An alternative approach, which avoids the use of an oxidant, is by formation of a sulphonium salt using CFjSOaCHzSiMea followed by ylide formation using caesium fluoride and rearrangement (Scheme 44). This method can run into difficulties if the starting thio-ester already contains an olefinic bond. 

This behaviour is illustrated in a preparation of the 2-thioxopenam (258) from the sulphoxide (259). Thus, pyrolysis of (259) induces a sulphoxide-sulphenate ester rearrangement followed by intramolecular trapping to give the disulphide (260) which is converted in two steps into the penam (258). ... 

Sulphur.—Compounds Containing Bivalent Sulphur. Attempts to oxidize bistrifluoromethyl sulphide (conveniently prepared by pyrolysis of commercial bistrifiuoromethyl disulphide at 425—435 °C) to either the sulphoxide or the sulphone using the reagents ( i-(n C H4-CO)sOa-100°C, NOjCIO, NOa-u.v., or NOa-Oa-350°C have proved unsuccessful fluorination of the monosulphide with hot argentic or cobaltic fluoride gave trifluoromethyl-sulphur pentafluoride, while bis(trifluoromethyl)sulphur difluoride was formed at low temperatures with fluorine itself. " Bis(trifluoromethyl)-sulphur difluoride and several other bis(perfluoroalkyl)sulphur difluorides, obtained from the corresponding sulphides and chlorine monofluoride (see p. 162), have been converted into bisperfluoroalkyl sulphoxides ... 

Apart from one citation, all the papers collected here to illustrate the reactions of vinyl sulphoxides deal with addition reactions. " As would be expected from the nature of the sulphoxide functional group, there are several novel features in these addition reactions compared with those of other vinyl compounds. Pyrolysis of alkyl styryl sulphoxides gives benzothiophens. The proposed mechanism, which involves formation and homolysis of a sulphenic acid followed by cyclization, (54) (55), is supported by the formation of benzo-... 

Kingsbury, using phenyl benzyl sulphoxide carbanion generated with organolithium reagents, has shown that condensation of sulphinyl carban-ions with benzaldehyde leads predominately to the threo-isomer of the 2-sulphinylcarbinol (96). Pyrolysis of the carbinol afforded a ketone. 

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