Dimethylsulfoxonium ylide

Examine electrostatic potential maps for dimethylsulfonium and dimethylsulfoxonium ylides. Which contains the more negatively-charged carbon Do either or both of the ylides incorporate a fully formed 7U bond Compare bond distances involving methylene and methyl carbons. Also examine the highest-occupied molecular orbital (HOMO) for evidence of 7U bonding. 

Electrostatic potential map for dimethylsulfoxonium ylide shows negatively-charged regions (in red) and positively-charged regions (in blue). 

Vinyl azides follow the same course of reaction when treated with dimethylsulfoxonium ylide in dimethyl sulfoxide at room temperature for 12 hr and high yields of clean 1-vinyltriazolines are obtained.378... 

Furthermore, vinyl azides (319) react with dimethylsulfoxonium ylide (320) at the azide function to produce in high yield l-vinyl-A -l,2,3-triazolines (321) (evouii, 75Ci(L)278, 81TL1863). 

Dimsylsodium (22) is an important reagent and it can be used for carbon-carbon bond formation (see Chapter 10, p. 187). DMSO may also be used in the Moffatt oxidation (see Chapter 5, p. 66) and by alkylation it can be converted into the corresponding dimethylsulfoxonium ylide which is valuable in organic synthesis (see Chapter 10, p. 187).4... 

Schomaker et al found that the Payne rearrangement is useful for controlling the regioselectivity of the reaction of dimethylsulfoxonium ylide with the epoxy alcohol 22. Thus the rearrangement of chiral non racemic epoxy alcohol 21 led to the more sterically accessible terminal epoxide 22, which then underwent nucleophilic epoxide opening with the ylide at C-1 to afford bis alkoxide 23. The 5-exo-tet ring closure of 23 resulted in the formation of 2,3-disubstituted tetrahydrofuran ring 24. 

The mechanism was also supported by the observation of quantitative formation of an insertion (initiation) product F2B-CH2-F as a result of the reaction of BF3 with diazomethane at -40°C to around -60°C [18], As described later in this review for the Pd-mediated polymerization of diazocarbonyl compounds and the B-mediated polymerization of dimethylsulfoxonium ylides, this type of mechanism is significant as a general one for PSMS with a combination of coordination (nucleophilic addition) and 1,2-migration for the metal-mediated reactions. 

In contrast to dimethylsulfoxonium ylide, for which introduction of substituents into the ylide carbon is difficult, the yUde carbon in (dimethylamino)phenyloxo-sulfonium ylide can be modified to have a substituent. For example, methyl-substituted (ethylide) analogue, (dimethylamino)phenyloxosulfonium ethylide 13,... 

A convenient route to A -isoxazoline N-oxides has been developed from nitrostyrenes using dimethylsulfoxonium methylide. The addition of the ylide (572) to the nitrostyrene (571) was greatly facilitated by the presence of copper(I) salts, the isoxazoline N-oxide (573) being obtained in excellent yield (76JOC4033). 

The Corey-Chaykovsky reaction entails the reaction of a sulfur ylide, either dimethylsulfoxonium methylide (1, Corey s ylide, sometimes known as DMSY) or dimethylsulfonium methylide (2), with electrophile 3 such as carbonyl, olefin, imine, or thiocarbonyl, to offer 4 as the corresponding epoxide, cyclopropane, aziridine, or thiirane. ... 

Sulfur ylides have several applications as reagents in synthesis.282 Dimethylsul-fonium methylide and dimethylsulfoxonium methylide are particularly useful.283 These sulfur ylides are prepared by deprotonation of the corresponding sulfonium salts, both of which are commercially available. 

Whereas phosphonium ylides normally react with carbonyl compounds to give alkenes, dimethylsulfonium methylide and dimethylsulfoxonium methylide yield epoxides. Instead of a four-center elimination, the adducts from the sulfur ylides undergo intramolecular displacement of the sulfur substituent by oxygen. In this reaction, the sulfur substituent serves both to promote anion formation and as the leaving group. 

Dimethylsulfonium methylide is both more reactive and less stable than dimethylsulfoxonium methylide, so it is generated and used at a lower temperature. A sharp distinction between the two ylides emerges in their reactions with a, ( -unsaturated carbonyl compounds. Dimethylsulfonium methylide yields epoxides, whereas dimethylsulfoxonium methylide reacts by conjugate addition and gives cyclopropanes (compare Entries 5 and 6 in Scheme 2.21). It appears that the reason for the difference lies in the relative rates of the two reactions available to the betaine intermediate (a) reversal to starting materials, or (b) intramolecular nucleophilic displacement.284 Presumably both reagents react most rapidly at the carbonyl group. In the case of dimethylsulfonium methylide the intramolecular displacement step is faster than the reverse of the addition, and epoxide formation takes place. 

Another difference between dimethylsulfonium methylide and dimethylsulfoxonium methylide concerns the stereoselectivity in formation of epoxides from cyclohexanones. Dimethylsulfonium methylide usually adds from the axial direction whereas dimethylsulfoxonium methylide favors the equatorial direction. This result may also be due to reversibility of addition in the case of the sulfoxonium methylide.92 The product from the sulfonium ylide is the result the kinetic preference for axial addition by small nucleophiles (see Part A, Section 2.4.1.2). In the case of reversible addition of the sulfoxonium ylide, product structure is determined by the rate of displacement and this may be faster for the more stable epoxide. 

Af-Unsubstituted 1,2,4-diazaarsoles are directly alkylated by diphenyl diazomethane, diazo esters, sulfur ylides, and alkyl vinyl ethers <90TL7607, 95HAC403). 1-Alkyl-1,2,4-diazo-arsoles (12) (R = Me, CHPhj) react with dimethylsulfoxonium yhde to give bicyclic arsiranes (13) (Equation (1))... 

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. 

Figure 9.4 shows stereogenic epoxide formations with S ylides and a ketone. The substrate is a conformationally fixed—because it represents a trans-decalin—cyclohexanone. Both the dimethylsulfoxonium methylide and the dimethylsulfonium methylide convert this cyclohexanone into an epoxide diastereoselectively. As Figure 9.4 shows, the observed diastereoselectivities are complementary. The sulfoxonium methylide attacks the carbonyl carbon equatorially, whereas the attack by the sulfonium ylide takes place axially. 

Unstabilized sulfonium ylides such as dimethylsulfonium methylide (3.45) and stabilized sulfoxonium ylides such as dimethylsulfoxonium methylide (3.46) are the most widely used sulfur ylides. 

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. 

Dimethylsulfoxonium methylide reacts with AT-selenoacylamidines to give 4,5-dihydro-l,3-selenazoles 33. The reaction pathway involves the addition of the sulfur ylide to the imine bond of the heterodienes, and then cyclization by a subsequent intramolecular substitution of the dimethylsulfoxonium leaving group (Scheme 17) <1998T2545>. 

Oxiranes can be prepared in excellent yield from carbonyl compounds by alkylidene transfer with sulfonium ylides. The reaction is generally carried out with dimethylsulfonium methylide 77, dimethylsulfoxonium methylide 78, or related compounds such as anionoid species originating from sulfylimines 79 and sulfox-imines 80 that can undergo addition to the electrophilic carbonyl carbon. 

In the first step of this reaction sequence, the primary alcohol 21 is oxidized to the corresponding aldehyde 38 in a Parikh-Doering oxidation which is related to the Swern oxidation. In general, this type of oxidation is conveniently carried out by addition of a solution of pyridine-SOs complex in DMSO to a mixture of the alcohol, DMSO and NEts. It can be assumed that dimethyl sulfoxide and sulfur trioxide react to form 0-dimethylsulfoxonium sulfate 40, which then further reacts with primary alcohol 39 to give 0-alkyl dimethylsulf-oxonium intermediate 41. Then, sulfonium salt 42 is formed and subsequently deprotonated by NEts to give sulfonium ylide 43. Finally, an intramolecular p-elimination occurs to provide the desired aldehyde 44 and dimethyl sulfide. 

Dithioesters like (62) which can exist in the enol form react with sulfur ylides like dimethylsulfoxonium methylide (63) to give ketenethiols (64). The mechanism of the reaction involves nucleophilic attack by the ylide on the enol form of (62) (Scheme 34). Similar compounds (65) may be synthesised by treatment of a suitable thioester (62) with an alkyl halide in the presence of a base (Scheme 35). 

On the other hand, with the less reactive dimethylsulfoxonium methylide (33), the slower reaction afforded the thermodynamically controlled epoxide (36). In this case, the more stable sulfoxonium ylide is better leaving group and the slower reaction allows reversible betaine formation, leading to the thermodynamic product (36) (Scheme 15). 

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