Reactions with sulphur ylides

Epoxides can be synthesised by the action of aldehydes or ketones with sulphur-ylides. They can also be prepared from alkenes by reaction with m-chloroperoxybenzoic acid. 

H]Squalene, 155, and [3- H]-2,3-oxidosqualene, 156, the key compounds in studies of the biosynthesis of sterols have been obtained according to the route shown in equation 53, which involves the modified Wittig reaction of [l- H]trisnorsqualene aldehyde 157 with phosphorus ylide to give 155 or with sulphur ylide to give 156 in high radiochemical yield and high purity. 

There is evidence, however, that these reactions may not involve conversion of the iodonium ylide into a carbene which then adds to the relevant substrate, but that this substrate is involved prior to cleavage of the carbon-iodine bond [136]. Other ylide interchange reactions which have been recorded include the conversions of various ylides into an oxosulphonium ylide by reaction with sulphur monoxide, generated in situ [141] ... 

The methylene insertion reactions have been found to proceed better in ionic liquids such as [bmin] [PFJ or [bmin] [BFJ on treatment with sulphur ylides. Sulphur ylides are obtained in situ by the reaction of alkyl halides with sulphides. The reaction works equally well with preformed sulphonium salts (Scheme 10). 

Unsaturated branched-chain sugars are mentioned in Chapters 13 and 16, and reactions of nitro-alkene carbohydrates with sulphur ylides are covered in Chapter 9. 

A useful method for the direct epoxidation of carbonyl compounds involves reaction of an unstabilized arsonium ylide (10) with an aldehyde or ketone, analogous to the reactions of sulphur ylides. Unlike previous methods, the reaction of (10) to form (11) proceeds with a high degree of stereochemical control, and most aldehydes react cleanly giving frans-oxirans. Drawbacks to the method are (i) the toxicity of arsenic, and (ii) the fact that since PhaAs is... 

Reaction of (CpMn(C0)2 THF)] with sulphur ylides (Me2N)RSO(CH2) produces Mn2( t-CH2)(C0)4CP2] or with ben2yl azide, [Mn2 it-CON(CH2Ph)N2 (CO)3Cp2), an intermediate in the formation of benzyl Isocyanate. 

Stabilised sulphur ylides react with alkenylcarbene complexes to form a mixture of different products depending on the reaction conditions. However, at -40 °C the reaction results in the formation of almost equimolecular amounts of vinyl ethers and diastereomeric cyclopropane derivatives. These cyclopropane products are derived from a formal [2C+1S] cycloaddition reaction and the mechanism that explains its formation implies an initial 1,4-addition to form a zwitterionic intermediate followed by cyclisation. Oxidation of the formed complex renders the final products [30] (Scheme 8). 

Trialkyl(2-borylvinyl)stannanes react with sulphur bis(trimethylsilylimide) to yield heterocyclic ylide compounds, as shown in reaction 21277. 

The use of dimethylsulphoxonium methylide, as a specific methylene insertion reagent for a, /J-unsaturated ketones and esters, is illustrated by its reaction with ethyl crotonate in dimethylformamide solution to form (39) (Expt 7.16).12 The sulphur ylide initially attacks the /J-carbon of the conjugated system (Michael acceptor site), and this is followed by cyclisation and loss of dimethyl sulphoxide. 

Chiral cyclopropanes geminally substituted with two EWGs (259) are obtained when alkenes, complexed with Fe carbonyls (257), are treated which sulphur ylides bearing an EWG (equation 78). Reaction of cyanosulphoniummethylide (260) with electron-... 

The recently described sulphur ylide diphenylsulphonium cyclopropylide (172), which converts saturated ketones into spirocyclobutanones, reacted with a steroidal 4,6-dien-3-one in a more complex manner. Two moles of the reagent were incorporated to give the spiro[2,4]heptan-4-one (173) and the epimer at the C-3 position of the steroid. Scheme 7 illustrates the likely reaction path. ... 

Reaction at Sulphur Thiophen Dioxides. - The stable S-ylide (167) was formed, in 40% yield, in the reaction of 2-isobutenylthiophen with dimethyl diazomalonate in the presence of rhodium acetate.The transient thiophen... 

Miscellaneous. The unusual reductions of benzyltriphenylphosphonium salts with sodium to give benzyldiphenylphosphine have been shown to involve reduction of the benzylidenephosphorane. This ylide with sulphur in benzene at 70 °C gave triphenylphosphine sulphide, a pentasulphide formulated as (45) or (46), and only traces of isomeric stilbenes. Previous workers reported high yields of stilbenes from the same reaction carried out in refluxing toluene. Benzoylmethylenetriphenylphosphorane (47) with sulphur gave a polymer of the thioaldehyde (48). 

Carbenes can also be trapped by thioamides as in the reactions of the carbenes obtained by irradiation of564. The possibility is that a sulphur ylide is formed in this system and the subsequent intramolecular reaction with the amide nitrogen affords the final products 565. Even in simple systems an ylide can be formed, as in the reaction of singlet methylene with acetone. ... 

Reactions of Thiophen Aldehydes and Ketones.—The synthesis of bis-(4-methylpent-3-enyl)thiophens was achieved by applying the Wittig reaction to (106). A convenient method for the synthesis of (2-thienyl)ethylene oxide from thiophen-2-aldehyde and a sulphur ylide has been worked out. From 2-thenil and diethyl ketone, (107) was prepared, and its Diels-Alder reactions have been studied. The reaction of (108) with different Grignard reagents has been... 

Johnson and Katekar have found that when one of the sulphur substituents in a sulphoximine was an alkyl group, treatment with a strong base such as sodium hydride would remove a proton alpha to sulphur to form a sulphoximine ylide. Thus, phenyl methyl sulphoxide with tosyl azide formed the sulphoximine (109). Treatment with sodium hydride apparently formed the ylide (110), as evidenced by its reaction with acetophenone to form a-methylstyrene oxide in 68% yield. By a similar... 

Several bi- and tri-cyclic thiepan derivatives were obtained by autoxidation of the cyclobutadiene (111) or by various reactions with strained sulphur-containing acetylenes, e.g.. the dithiet (112). The ylides derived from cis- and trans-ill) were alkylated stereoselectively at low temperatures, and they reacted with carbonyl compounds to give ring-opened oxirans (113). Reduction of the 6-methoxy-carbonyl derivative of (72) afforded the ten-membered cyclic sulphide (114). ... 

The sulphur ylide Cr[CH2S(0)Me21(CO)5 reacts with (Ph2P)2C=CH2 to form the electrophilic CrTcH pTPhT cT=CH TpPh2](CO)4.In related reactions with (R2P)(RnE)C=PR3 the analogous complexes CrTcH PPh HI=PRj7pPh2 ] (CO) 4 arise (ERjj = PR2 SPh R various... 

Considerable attention has been focussed recently upon the reaction of car-benes with sulphur compounds, and there are now many examples of stable sulphonium ylides. The first example of a rearrangement within this series has been reported by Benati et aL, with formation of the dibenzothiepin (251). 

Thus, Simonneaux and co-workers have reported treatment of methyl allyl sulphide with 2-diazoethyl acetate at 25 in the presence of (SBF>4PRuCO as catalyst (homogeneous reaction, entry 1 in Table 4), which leads to ethyl-2-(methylthio)pent-4-enoate in 88 % yield with 8 % of dimers [56]. As presented in Scheme 21, the formation of ethyl-2-(methylthio)pent-4-enoate derives from the [2,3]-sigmatropic rearrangement of the sulphur ylide and that of the dimers (di-ethylfumarate and diethylmaleate) derives from 2-diazoethyl acetate dimerization. 

Dibromocarbene generated under phase-transfer conditions inserts into the a-C-H bond of ( -l,3-hexadiene)Fe(CO)3 to give (74) a similar reaction occurs with (chd)Fe(CO)3. Diazomethane reacts with triene (75) to give (76) on oxidation with Ce +, nitrogen extrusion to yield the cyclopropane derivative occurs, in addition to decomplexation. Reaction of (75) with the sulphur ylide (CH3)2 S=CHC02Me proceeds similarly to give (77).Methods for the addition of carbene and dichlorocarbene to the unco-ordinated double bonds of (cot)Fe(CO)3 and (chpt)Fe(CO)3 have been described. 

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