Ylides sulphur

It has now been found that in place of strong base (like alkyl lithium), a PTC like in presence of aq. NaOH can be used.  

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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). 

Dialkyl sulphides are converted into trialkylsulphonium salts by treatment with an alkyl halide (the bromide or iodide is usually the reactant of choice). An important example of this group is trimethylsulphonium iodide, which is used as a methylene transfer reagent by virtue of its being converted in the presence of base into a sulphur ylide, which is a nucleophilic carbene equivalent. 

The synthesis of 3-benzylcyclobutanone (3) is an illustration of an overall intramolecular alkylation of an acyl anion equivalent (Section 5.9). The a,a>-dihalide is 2-benzyl-l,3-dibromopropane, and the acyl anion equivalent is methyl methylthiomethyl sulphoxide2 the product is 1-methylsulphinyl-l-methylthio-3-benzylcyclobutane which is obtained as a mixture of cis/trans isomers [(9) and (10)] (Expt 7.3). Aqueous acid hydrolysis in ethereal solution unmasks the carbonyl group. The possible mechanism of the reaction is via a Stevens-type rearrangement of the intermediate sulphur ylide, which may proceed in a pericylic, radical or ion pair fashion. 

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. 

Deprotonation of this intermediate gives a sulphur ylide, which undergoes intramolecular deprotonation via a five-membered ring transition state and fragmentation to yield the product and DMS (odour ) ... 

Formation of sulphur ylide complexes of Pt(Pd) of type [PtX2(R2S)Sy] (X = Cl, Br or I R = Me, Et Sy = Me(Ph)SCHC(0)C6H4Cl-p) has been reported.105 The v(CO) band of the metal complexes occurs at higher frequencies than in the free ylide, and in addition spin-spin coupling between the ylide methine proton and the 195Pt nucleus is observed, which is indicative of the Pt—C bond (47). 

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. 

Hi. MIRC reactions mth ylides. Numerous cyclopropane derivatives have been synthesized via methylene transfer generated from sulphur ylides, such as dimethylsulpho-xonium methylide, to electron-deficient alkenes. This is shown in the examples in... 

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-... 

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. 

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. ... 

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... 

Prenyl rearrangement. To date, only 4-prenyl-, but no 4-tert-prenylindoles have been synthesised. Rainier and co-workers exploited an interesting sequence of sulphur ylide Claisen rearrangement and Cope rearrangement to achieve C4-prenylation of 2-thioindoles (Scheme 51) [201]. Sulphur ylide intermediate... 

Scheme 51 Sequential sulphur ylide Claisen and Cope rearrangements leading to C4-prenylation of indole [201]...

Nozahi, H., Z. Morita, and K. Kond Stable Sulphur-Ylides from Sulfoxides and ActiveMethylene Compounds.TetrahedronLetters (London) 25,2913 (1966). 

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