Sulfur ylides reacting with ketones

Sulfur ylides react with ketones to give epoxides. Suggest a mechanism for this reaction. 

Sulfur ylides react with aldehydes and ketones to form epoxides (oxiranes) ... 

The use of sulfur in place of the phosphorus brings about a different mode of decomposition of the intermediate betaine. Two sulfur ylides, dimethylsulfonium methylide (Scheme 3.49a) and dimethylsulfoxonium methylide (Scheme 3.49b), have been used. Both ylides react with ketones to give epoxides, but the stereochemistry may differ. 

EDSA reacts with anhydrides (also acid chlorides, acetylenic esters and ketones) to give stable sulfur ylides and with a-diketones to give epoxy esters.3... 

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. 

There is an important difference between the reactions of these sulfur ylides and the analogous phosphorus ylides with carbonyl compounds. Whereas phosphorus ylides react with aldehydes and ketones to yield alkenes, dimethylsulfonium methylide and dimethyloxosulfonium methylide yield epoxides. Instead of a four-center elimination in the zwitterionic intermediate, intramolecular nucleophilic displacement by oxygen occurs. 

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. 

In the Swern oxidation, the reaction of oxalyl chloride with DMSO may generate chlorodimethylsulfonium chloride (A), which reacts with the alcohol to give alkoxysulfonium ion intermediate B. The base, typically triethylamine, deprotonates the alkoxysulfonium ion B to give the sulfur ylide C, which decomposes to give DMS and the desired aldehyde or ketone (Scheme 7.7). The temperature of this reaction is kept near —60 to -78°C. 

Nakayama and co-workers established that carbonyl-stabilized sulfur ylide (83) reacted with elemental selenium to afford 1,3-oxaselenole (85) in good yield (85TL2201). The reaction was presumed to proceed through the intermediacy of selenal (84). Subsequently, support for this mechanism has come from the isolation of adduct 86 when the reaction is performed in the presence of dimethylbutadiene (87TL4423). Other Diels-Alder reactions of intermediate a-oxoseleno-aldehydes and -ketones were also found... 

The dehydrogenation of bis(a-bromobenzyl) sulfide (41) with Fe2(CO)9 in the presence of furan affords (43). The iron-stabilized sulfur ylide (42) has been proposed as intermediate. Reaction of C -di-phenylnitrone (44) with l,2-bis(methylene)-3,3.4,4,5,5-hexamethylcyclopentane (45) in benzene at 80 C gives a [4 -I- 3] cycloadduct (46 18%), along with some other products. Landor et al. have shown that the dehydrobromination of allenyl bromide (47) in the presence of furan affords bicyclic ketone (49) in 9% yield. Apparently, a strain alkyne intermediate reacts with r-butyl alcohol to afford an enol ether (48), which is then converted to (49) (Scheme 11). 

Early efforts to probe the stereochemistry of sulfur ylide additions have been reviewed. Ylide (1) reacts with unhindered cyclohexanone derivatives to give products resulting from axial attack, whereas (2) gives rise to net equatorial addition. This is again due to the tendency of (1) to undergo l etically controlled reactions and (2) to give products resulting from thermodynamic control. However, equator attack may prevail even in kinetically controlled reactions if axial attack is rendered sufficiently hindered, e.g. by 1,3-diaxial interactions or by additional steric bulk adjacent to the reactive caibonyl. For example, the addition of (1) to ketone (9) afibrds the -epoxide shown in equation (6) exclusively. Other cyclic systems react with fairly predictable stereoselectivities in accord with the above observa-... 

Dimsylsodium (24) functions as a highly basic sulfur ylide. It can be used to convert phosphonium salts to phosphorus ylides for use in the Wittig reaction. Dimsylsodium also reacts with aldehydes and ketones by nucleophilic addition to form epoxides and with esters by nucleophilic substitution to yield p-ketosulfoxides (25) (Scheme 11). The p-ketosulfoxides (25) contain acidic a-hydrogens which can be readily removed to allow alkylation, and the products (26) suffer reductive desulfuration on treatment with aluminium amalgam to yield ketones (27) (Scheme 11) This procedure can, for instance, be applied to the conversion of ethyl benzoate to propiophenone (28) (Scheme 12). 

Although the sulfur ylide A does not react with simple ketones, the carboxylate analog B does, leading to epoxides. Explain the difference in reactivity. 

Stabilized Sulfur Ylides. Acid chlorides, anhydrides, and isocyanates acylate EDSA to generate good yields of stabilized sulfur ylides. In addition, alkynes conjugated with either ketones or esters react in a similar fashion (eq 2). ... 

Generation of Sulfur Ylide Julia Olefination and Related Reactions. The deprotonation at a position a to a sulfone group is effected using a strong base, t3q)ically n-butyllithium or LDA, to give an anion which then reacts with an aldehyde or a ketone leading to the corresponding 8-hydroxy sulfone. There are, however, a number of examples where LHMDS was used as a base. For instance, sulfone 19 was deprotonated with LHMDS and then reacted with aldehyde 20 to produce 8-hydroxy sulfone 21 (eq 51)P... 

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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