Ylids sulfur

For a review of nitrogen ylids, see Musker, W.K. Fortschr. Chem. Forsch., 1970,14, 295. For a monograph on sulfur ylids, see Trost, B.M. Melvin Jr, L.S. Sulfur Ylids Academic Press NY, 1975. For reviews, see Fava, A. in Bemardi Csizmadia Mangini Organic Sulfur Chemistry Elsevier NY, 1985, p. 299 Belkin, Yu.V. Polezhaeva, N.A. Russ. Chem. Rev., 1981, 50,481 Block, E. in Stirling The Chemistry of the Sulphonium Group,... 

Sulfur ylids containing a benzylic group (analogous to 18) undergo an analogous rearrangement. 

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... 

Aldehydes and ketones can be converted to epoxides in good yields with the sulfur ylids dimethyloxosulfonium methylid (60) and dimethylsulfonium methylid (61). For most purposes, 60 is the reagent of choice, because 61 is much less... 

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... 

Sulfur ylids containing a Z group give an analogous rearrangement, often also referred to as a Stevens rearrangement. In this case too, there is much evidence... 

Addition of sulfur ylids or diazomethane to aldehydes or ketones... 

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). 

Although we do not know just how thiamine binds to the enzyme, the essential features of the reaction are quite well understood. Thiamine has an acidic hydrogen at the 2-position of the azathiacyclopentadiene ring, and you should recognize that the conjugate base, 10, is both a nitrogen ylid and a sulfur ylid (Section 16-4A) ... 

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... 

But how are we to make the epoxide 61 The obvious route is by epoxidation of the alkene 63. The alkene 63 could be made by a Wittig reaction (chapter 15) on the ketone 64 or directly by sulfur ylid chemistry (chapter 30). 

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. 

So what has this got to do with cyclopropanes If sulfur ylids react with enones either the epoxide 74 or the cyclopropane 76 may be formed.19 The general rule is that sulfonium ylids from 69 give epoxides but sulfoxonium ylids give cyclopropanes 76. 

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... 

Problem 9 in Chapter 32 asked you to interpret tile NMR trum of a cyclopropane (A). This compound was formed iga sulfur ylid. What is the mechanism of the reaction ... 

When sodium hydroxide was used as nucleophile, salt 3c was rapidly converted to alkyne 63. This alkyne now features only a single stereocenter, and this is evident from its spectra. Its structure was initially assigned incorrectly, but the alkyne structure (63) has been rigorously established by X-ray crystallography. It is curious that azide and hydroxide should attack on the periphery of the TTF ring system, while the bulkier malonate anion attacks internal carbons. It is also intriguing that none of the observed modes of attack give rise to the sulfur ylid 64, which should be more stable than 61. 

---