Reaction with sulfur ylids

Double-bond compounds that undergo the Michael reaction (15-21) can be converted to cyclopropane derivatives with sulfur ylids. Among the most common of these is dimethyloxosulfonium methylid (109), which is widely used to... 

The generally accepted mechanism for the reaction between sulfur ylids and aldehydes or ketone is which is similar to that of the reaction of sulfur ylids with... 

A modern example of an agent used against human fungal infections is Pfizer s fluconazole, which actually contains two triazoles. The first is added as the anion to an a-chloroketone and the second is added to an epoxide made with sulfur ylid chemistry (you will meet this in Chapter 46). Note that weak bases were used to catalyse both of these reactions. Triazole is acidic enough for even... 

A similar reaction assisted by electrostatic interaction is shown in Scheme 7. As is seen in this Scheme, the diaminochlorocyclopropenium ion readily reacts with sulfur ylid to give diamino triafulvenes 35). This reaction seems to proceed through the reaction intermediate 36) (Scheme... 

An interesting approach to azasugars (e. g. 116 in O Scheme 31) from the epoxsides built at the anomeric centers of unprotected carbohydrates was presented recently [78]. Such epoxides (e.g. 115) were obtained with very high selectivity hy reaction of the corresponding hemi-acetals (e. g. 114) with sulfur ylid (O Scheme 31). This reaction is applicable for various sugar aldehydes [79]. 

A) and used in organic synthesis. a-Lithio sulfides give useful carbanion reactions and sulfur ylids can be formed (secs. 8.6, 8.8.B). The difficulties in preparing primary and secondary amines by traditional methods (from halides or tosylates via reaction with imides or azides, sec. 2.7) make the hydroboration-amination sequence a mild and useful alternative for the synthesis of amines. 

Some 2,3-epoxyamides of aldonic acids have been prepared by reaction of acyclic aldose derivatives with sulfur ylids (Scheme 1). 5y -epoxidation of some racemic 2-benzyloxy-4-alkenamides by way of iodohydrin formation and subsequent base treatment has afforded epoxides such as 2. Epoxidation of hex-2-enopyranosyl phosphonates has been effected with H202/sodium tungstate. ... 

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

In the late 1960s, methods were developed for the synthesis of alkylated ketones, esters, and amides via the reaction of trialkyl-boranes with a-diazocarbonyl compounds (50,51), halogen-substituted enolates (52), and sulfur ylids (53) (eqs. [33]-[35]). Only one study has addressed the stereochemical aspects of these reactions in detail. Masamune (54) reported that diazoketones 56 (Ri = CH3, CH2Ph, Ph), upon reaction with tributylborane, afford almost exclusively the ( )-enolate, in qualitative agreement with an earlier report by Pasto (55). It was also found that E) - (Z)-enolate isomerization could be accomplished with a catalytic amount of lithium phenoxide (CgHg, 16 hr, 22°C) (54). 

The relative rates and stereochemistry of epoxidation reactions of 5-substituted-adamantan-2-ones with two sulfur ylids (methylenedimethylsulfurane and its oxy-sulfurane analogue) have been studied in DMSO and in benzene.318... 

The simplest sulfur ylids are formed from sulfonium salts 69 by deprotonation in base. These ylids react with carbonyl compounds to give epoxides.18 Nucleophilic attack on the carbonyl group 70 is followed by elimination 71 of dimethylsulfide 72 and formation of the epoxide 73. You should compare diagram 71 with diagram 23 in chapter 15. The phosphonium ylid reacted by formation of a P-0 bond and an alkene in the Wittig reaction. The sulfonium compound reacts by formation of a C-O bond 71 as the S-O bond is much weaker than the P-0 bond. The sulfonium salt 69 can be reformed by reaction of 72 with Mel. 

Sulfur ylids have traditionally been prepared by two principal methods (1) deprotonation of S-alkylsulfonium salts and (2) reaction of carbenes or carbenoids with thioethers (75MI1). Both methods have been applied to the... 

Just as sulfur ylids react with the carbonyl of an aldehyde or ketone to give an epoxide, tellurium ylids react with imines to give an aziridine. The reaction of an aUyhc tellurium salt, RCH=CHCH2Te Bu2 Br, with lithium hexamethyldisila-zide in HMPA/toluene leads to the tellurium yhd via deprotonation. In the presence of an imine, the ylid add to the imine and subsequent displacement of Bu2Te generates an aziridine with a pendant vinyl group. ... 

The sulfur ylid Me2S(0)CH2 is a very weak base, and, when coordinated to nickel in the complex [Ni( / -C2H4)2CH2S(0)Me2] (91), spontaneous decomposition to ethane, cyclopropane, and methane occurs (93). In another reaction, compound 92 rearranges under UV irradiation to yield, with insertion of iron into a phenyl-carbon bond, a cyclic carbene complex, 93 94). 

Reaction with an aldehyde starts by the removal of a proton with quite a weak base (usually a tertiary amine) to give the ylid 189 in which the negative charge is stabilised partly by electrostatic interaction (the ylid) and partly by the sulfur atom. Nucleophilic attack on the aldehyde gives 190 which can transfer a proton from C to O to give uncharged 191. 

Reactions of chiral allylic boranes with carbonyl compounds Reactions of chiral allyl boranes with imines Asymmetric Addition of Carbon Nucleophiles to Ketones Addition of alkyl lithiums to ketones Asymmetric epoxidation with chiral sulfur ylids Asymmetric Nucleophilic Attack by Chiral Alcohols Deracemisation of arylpropionic acids Deracemisation of a-halo acids Asymmetric Conjugate Addition of Nitrogen Nucleophiles An asymmetric synthesis of thienamycin Asymmetric Protonation... 

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