Ketones, unsaturated sulfur ylides

Until this work, the reactions between the benzyl sulfonium ylide and ketones to give trisubstituted epoxides had not previously been used in asymmetric sulfur ylide-mediated epoxidation. It was found that good selectivities were obtained with cyclic ketones (Entry 6), but lower diastereo- and enantioselectivities resulted with acyclic ketones (Entries 7 and 8), which still remain challenging substrates for sulfur ylide-mediated epoxidation. In addition they showed that aryl-vinyl epoxides could also be synthesized with the aid of a,P-unsaturated sulfonium salts lOa-b (Scheme 1.4). 

Dimethylsulfoxonium methylide (DMSY, also referred to as Corey s reagent) is a convenient methylene transfer reagent. It appears to be the most used sulfur ylide and a Tetrahedron Report [455] covers most of its chemistry (345 references). In contrast to dimethylsulfonium methylide, which must be used as soon as it is formed, DMSY is much more stable and can be stored for several days at room temperature. It is the reagent of choice in many instances. However, with a,(3-unsaturated ketones the two reagents react in different ways, as shown for cyclohexenone. 

This cyclopropanation method works well for a,/ -unsaturated aldehydes, ketones, esters, and nitriles and it has also been employed for the preparation of cyclopropylacylsilanes33. In this case a silyl-substituted sulfur ylide provides the desired cyclopropanes, but generally the trans selectivity is only moderate. 

Chiral aminosulfoxonium ylides react with electron-deficient alkenes, e.g. a,p-unsaturated ketones and esters, to cyclopropanes in moderate to high yields (56-94%) and up to 34% ee The chiral sulfur ylides A, and were reacted with various Michael acceptors, whereby enantioselectivities up to 53% were achieved. 

Acyl azoliums generated from enals have been converted to cyclopropyl carboxylic esters with ee < 99% by reaction with sulfur ylides. Some FLPs have been found to i react by conjugate P/B addition to unsaturated ketones and esters, whereas 1,2-addition to corresponding aldehydes is usual. ... 

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