Dimethylsulphoxonium methylide

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. 

The trienone (74), either by reaction with diazomethane and pyrolysis of the derived pyrazoline or by treatment with dimethylsulphoxonium methylide anion, yielded28 the 1 a,2 -methylene derivative (75). Epoxidation followed by the action of hydrogen chloride gave (77). The methylene bridge was re-formed by the reaction of collidine, the product being (76). Halogenated steroids of use in determining the metabolic fate of 16-chloro-oestrone methyl ethers and of chlormadinone acetate have been synthesized.29... 

A high-yield synthesis of deacetamidoisocolchicine (456), and therefore of colchicine into which it has been converted, has been accomplished from the methoxyquinone ketal (450). This dienone is treated with dimethylsulphoxonium methylide to give the enone (451), which with the appropriate Grignard reagent gives the tertiary alcohol (452, R=H). Treatment of... 

The spirocyclobutanone (290) is produced from a 16a-methyl-17-chloro-pregnan-20-one (288) and its 17-epimer by reaction with dimethylsulphoxonium methylide. In the absence of the 16a-methyl group, c.g. (289), the reaction is less selective, affording both the cyclobutanones (291) and (292). 

Reagents i, dimethylsulphoxonium methylide ii, isoamyimagnesium bromide iii, pyridinium chloro-chromate iv, MeOH-HCl v, HSCH2CH2SH-Bp3,Et20 vi, Raney nickel... 

Attempts to effect the direct addition of 2-lithio-l,3-dithian to 17-keto-steroids have met with limited success. On the other hand, reactions of 17-spiro-epoxides were found to provide convenient access to homopregnane derivatives. Whereas treatment of the 17-ketoandrostene (188) with dimethylsulphoxonium methylide gave an inseparable mixture of the two epimers (189) and (190), reaction of (188) with dimethylsuphonium methylide afforded exclusively the 17j3-oxiran (189) in high yield. Opening of the epoxide of (189) with 2-methyl-1,3-dithianyl anion proceeded smoothly to give the 17)S-hydroxy-dithian (191). 

Isoflavans and Isoflavylium Salts.—Cycloaddition of dimethylsulphoxonium methylide (183) to cyclohexanediones (or their enols) (182) gave good yields of 3,4,5,6,7,8-hexahydro-3-hydroxy-2//-l-benzopyran-5-ones (184). When the O-acetate (185) of this was pyrolysed at 150 °C, a 2 1 mixture of 2H- (186) and 4//-benzopyrans (187) was obtained. ""... 

The reactions of ketonucleoside (74 B=thyminyl, theophyllinyl) with dimethylsulphoxonium methylide have been investigated. Under certain conditions the q-L-galacto product (75) was produced, indicating epimerization at... 

The condensation of dimethylsulphoxonium methylide with ethylenic ketones ... 

Phenalenone (20 R = H) did not give the expected cyclopropylketone (21 R = H) on reaction with dimethylsulphoxonium methylide, attack at the 9-position instead generating the betaine (22X which collapsed to 9-methylphenalenone (20 R = Me). However, treatment of the latter gave the cyclopropane (21 R = Me). 

Dimethylsulphoxonium methylide continues to be used for olefin cyclopropana-tion, but the reagent appears to be of little use with -substituted styrenes since an alternative pathway which results in a 2-isoxazoline N-oxide is frequently followed. The diylide (144) undergoes condensation with electron-deficient olefins to give the... 

Condensatioii Reactions.—Little emphasis has been placed on the use of condensation reactions in cyclopropane synthesis during the past year. Dimethylsulphoxonium methylide has been used for cyclopropanation of the side-chain double bond in brassicasterol, a A steroidal diene, due to the failure of carbene and carbenoid additions. Michael addition of the ylide (136) to acrolein affords an isomeric mixture of cyclopropanes, whereas addition to acrylonitrile stereoselectively gives only one isomer, the identity of which has not been established. An analogous... 

The benzocyclobutenone (399) reacts with dimethylsulphoxonium methylide to give the indanone (400) rather than the expected epoxide (401). This is presumably a reflection of the strain in (399). 

The addition of dimethylsulphoxonium methylide to activated olefins is greatly facilitated by the presence of cuprous salts. Hence, 2l -isoxazine-7V-oxides were prepared in excellent yield from nitrostyrenes (Scheme 128)X ... 

The stereochemical course of the addition of dimethylsulphoxonium methylide to 3-arylidenechroman-4-ones (15) has been shown to be affected by the structure of (15). The results were interpreted by considering the steric interactions of the conformations of the zwitterionic intermediates. 

Thiophen-fused Tropylium Ions and Related Compounds.— The reaction of some thieno-tropones such as (241) with dimethylsulphoxonium methylide gave cyclopropane derivatives (242). The reaction of (241) with electrophilic reagents has been studied. The synthesis of compounds of type (241) has been modified... 

The reaction of diphenyl trithiocarbonate with phenyl-lithium, which takes place at -78 °C to form (446), constitutes a further example of a thiophilic addition to the thiocarbonyl double bond. Compound (446) appeared to be stable in solution below -20 C, and its structure was confirmed by its reactions with deuterium oxide and methyl iodide, affording (447) and (448), respectively. Dimethyl trithiocarbonate reacted with two equivalents of dimethylsulphoxonium methylide to form... 

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