Dimethylsulphonium methylide

The plant bufadienolide scillarenin (500) has been synthesized. The starting material was 15a-hydroxycortexone (501), which was converted into the diketone ketal (502) by cupric acetate oxidation at C(21), followed by selective ketalization and tosylate elimination. Protection at C(3) as the dienol ether, oxiran formation at C(20) with dimethylsulphonium methylide, and regeneration of the C(3)- and C(21)-oxo-groups by acid hydrolysis then provided (503). Selective reaction at C(21) with the sodium salt of diethyl methoxycarbonyl-methylphosphonate, and boron trifluoride rearrangement of the epoxide ring to the aldehydo-unsaturated ester (504), was followed by enol lactonization to the bufadienolide (505). This was converted, in turn, to scillarenin (500) via the 14,15-bromohydrin, by standard reactions. Unsubstituted bufadienolides have also been prepared by the same method. 

Two short syntheses of 14a-bufadienolides have been described in which either of the aldehyde derivatives (12) or (15) are treated with carbomethoxy-methylenediethylphosphonate to give the unsaturated esters (13) and (16). The former was then cyclised directly to the bufadienolide (14) whilst (16) was converted to the free aldehyde (17) before cyclisation. The aldehyde derivatives (12) and (15) are readily prepared by short reaction sequences involving reaction of the dimethyl acetal (18) with either methoxymethylenetriphenylphosphorane or dimethylsulphonium methylide. Use of this latter route gives the spiro-epoxide... 

A new method for the preparation of hydroxyamines, e.g. (317), from 17-ketones which provides a route to D-homo-androstanes in high yield has been devised. Methylenation of the 17-ketones with dimethylsulphonium methylide or dimethyl-sulphoxonium methylide affords, in almost quantitative yield, (and stereo-selectively in the case of the former reagent) the oxirans (315) which are readily converted into hydroxy-azides (316). 

A novel method for the stereospecific synthesis of 17a- and 17) - homocorticoid side-chains from 17-ketones has been developed.The 17-oxiran (520), obtainable in high yield from the 17-ketone and dimethylsulphonium methylide, reacts with 2-lithio-2-methyl-l,3-dithian to afford (521) which on further treatment gives the 17-iso- homocorticoid (522) in high overall yield. Similar reaction of the 17-epimeric oxiran, which could not be separated from (520), afforded the normal... 

New uses for pyrylium salts include their reaction with azo-methines and ammonia to give 4-aminopyridines [e.g., (22)],37 with dimethylsulphonium methylide to yield the phenol (23) and with the anion of nitromethane to form the nitrophenol (24).38 The addition of lithium phenylacetylene to 2,6-diphenylpyrylium perchlorate in boiling ether has now been shown to form the pyran (25) but in THF at room temperature a dimeric product (26) is obtained.39 Its... 

Dimethylsulphonium methylide reacts with trimethyl- or triphenyl--cyclopropenium salts to provide trisubstituted thiophenes [53] ... 

The epoxide-forming reaction of sulphonium ylides with carbonyl compounds continues to be widely applied in a routine sense at the same time as new and unique applications are studied. Bravo et al. have reported that, whereas indole and dimethylsulphonium-methylide afford iV-methylindole (i.e. protonation of the ylide followed by sulphonium salt alkylation of the indole), the keto-amide (28) gives an epoxide. Similarly, the amide function in (29) did not interfere with epoxide formation. In... 

The cyclization of o-bcnzylthiobenzyl cyanides (326) with aluminium bromide gives 2-aminobenzo[6]thiophens (327). A new synthesis of benzothiophens is based upon the reaction of o-mercapto-aromatic ketones or their xanthates (328) with dimethylsulphonium methylide. The... 

Carbon atom insertion. Stereospecific formation of cw-epoxide (81) from nopinone (80) using dimethylsulphonium methylide, has been reported. The exclusive formation of (81) is considered to be a result of steric interactions favouring the intermediate conformation shown. The isolation of... 

The first isolation of a heterocyclic bicyclobutane (258) has been achieved by the reaction of 2-phenylazirine with dimethylsulphonium methylide. 

Dimethylsulphonium methylide methylates aromatic E-oximes in yields of 32—91% and trimethylsulphonium hydroxide methylates, in excellent yield, carboxylic acids, thiols, phenols, and certain heterocyclic nitrogen atoms. However, aromatic amines and alcohols remain unchanged. Polymer-bound reagents have proved popular in recent years such a reagent, a polymer-bound sulphonium ylide, provides excellent yields of epoxides from ketones. The spent reagent may then be regenerated for further use. Nitroalkanes are reduced, in... 

Dihydrofurans and Tetrahydrofurans.—Silver (i)-catalysed cyclizations of allenic alcohols lead to 2,5-dihydrofurans in moderate yields (Scheme 23). ° Dimethylsulphonium methylide reacts smoothly with o- and p-hydroxy-benzylidene ketones to yield 2,5-dihydrofurans. " Quinone methides, as inter-... 

Reduced Furans.—Very high yields of furan derivatives that bear substituents that are useful for further modification have been obtained by the reaction of bis(methylthio)propenones (20) with dimethylsulphonium methylide. ... 

Several ylide-metal complexes have been reported recently. These complexes include palladium(ii), platinum(n), and mercury(n) complexes with keto-stabilized sulphonium ylides, with dimethylsulphonium methylide, and with dimethyl-sulphonium dicyanomethylide, as well as chromium, tungsten, molybdenum, and manganese complexes with dimethylsulphonium cyclopentadienylide. ... 

Three separate reactions with the cyclopropene system have been reported. Dimethylsulphonium-methylide with triphenylcyclopropene... 

The reaction of dimethylsulphonium-methylide with triphenylcyclo-propylium bromide produced a 1 1.7 ratio of the thiophen (79) and the thioketone (80). Formation of a new ylide (81) as an intermediate was proposed, with ring expansion to an SS-dimethylthiophen and loss of ethane... 

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