Sulfonium salts diazo compounds

Sulfonium ylides generated through base-promoted deprotonation of sulfonium salt have been extensively studied. The reaction of sulfides with a diazo carbonyl compound in the presence of a transition metal catalyst is an alternative approach to obtain sulfonium ylides. Sulfonium ylides are more stable than the corresponding oxonium ylides. Stable sulfonium ylides generated by the reaction of an Rh(ii) carbene complex with thiophene have been reported (Figure 5). ... 

Free carbene 429 generated by photolysis or thermolysis of the diazo compound cyclizes into the sulfonium ylide, which undergoes a thia-Stevens rearrangement to 430 in 19% yield. The same result was obtained using the corresponding p-tosylhydrazone sodium salt as a carbene precursor (83JA6096). Rh(II)-catalyzed decomposition of sulfur-containing diazo... 

Sulfur ylides are useful reagents in organic synthesis. The ylide is formally a zwitterion in which a carbanion is stabilized by interaction with an adjacent sulfonium centre. They are usually prepared by proton abstraction from a sulfonium salt with a suitable base or by reaction of a sulfide with an alkylating agent such as Me30+BF4 or a carbene formed, for example, by metal-catalysed or photolytic decomposition of a diazo compound (1.103). 

The ylide, of general structure (4.132), is formed by reaction of the corresponding sulphide (4.133) with a metallocarbenoid resulting from transition metal salt-mediated decomposition of a diazo compound (4.134) or N-tosyl hydrazone salt (4.135). Reaction of the sulfonium ylide (4.132) with aldehyde (4.136) yields the trans-epoxide (4.137) as the major product and sulfide (4.133) which is then returned to the catalytic cycle (Figure 4.10). 

In catalytic epoxidation reactions an alternative to the ylide generation method via alkylation/deprotonation is the transition metal-mediated carbene transfer from diazo compounds to sulfide catalysts. In 1994, Aggarwal and coworkers employed this method in the enantioselective catalytic epoxidation of aldehydes [25]. Using 20mol% of non-racemic sulfide 17 and lmol% of Rh2(OAc)4 together with the slow addition of PhCHN2, a 58% yield and 11% ee were obtained in the epoxidation of benzaldehyde (Scheme 20.10). The enantioselectivity was similar to the results obtained by Breau and Durst using preformed sulfonium salts [26]. 

Salts of ammonium, oxonium, sulfonium, etc., are placed under the formula of the corresponding hydroxide. (C6H5)2lCl is found under C12H11OI. Diazo-nium compounds are handled in the same manner, under the corresponding amine. 

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