Dimethylsulfonium

The dimethylsulfonium ylide (568) added readily to aroyl isocyanates to give the intermediate addition product (569). This on heating underwent ring closure with loss of dimethyl sulfide to form the 4-hydroxyoxazole (570) (73T1983). This normal C-acylation of the sulfonium ylide also leads to thiazoles with thiobenzoyl isocyanate in this case the initial acylation product was not isolated, the thiazole being obtained directly. 

Dimethylsulfonium phenacylide (574) underwent C-alkylation with a-chloronitroso compounds such as (575). The intermediate (576) immediately cyclized to the isoxazoline (577). With a more basic ylide such as dimethylsulfonium methoxycarbonylmethylide the initial alkylation product underwent elimination of the sulfonium group to an alkene rather than its displacement (72T3845). 

The reaction of benzonitrile oxide with dimethylsulfonium methylylide or triphenylar-sonium methylylide produced 3-phenyl-2isoxazoline (Scheme 116) (67MI4I602, 68G48). A similar reaction of benzonitrile oxide with diazomethane likewise gave 3-phenyl-2-isoxazo-line via intermediate (470) (Scheme 117). 

Bravo et al. studied the reaction of various ylides with monooximes of biacetyl and benzil. Dimethylsulfonium methylide and triphenylarsonium methylide gave 2-isoxazolin-5-ol and isoxazoles, with the former being the major product. Triphenylphosphonium methylide and dimethyloxosulfonium methylide gave open-chain products (Scheme 135) (70TL3223, 72G395). The cycloaddition of benzonitrile oxide to enolic compounds produced 5-ethers which could be cleaved or dehydrated (Scheme 136) (70CJC467, 72NKK1452). 

Carbanions in the form of ylides also add to azirines. For example, treatment of 1-azirine (227) with dimethylsulfonium methylide gives 1-azabicyclobutane (229) in good yield (72JA2758). The addition of the methylene group occurs by initial nucleophilic attack by the ylide to give intermediate (228) which cyclizes with expulsion of dimethyl sulfide. 

The leaving group also affects the amount of internal versus terminal alkene that is formed. The poorer the leaving group, the more El cb-like is the transition state. This trend is illustrated for the case of the 2-butyl system by the data in Table 6.6. Positively charged leaving groups, such as in dimethylsulfonium and trimethylammonium salts, may favor a more El cb-like transition state because their inductive and field effects increase the acidity of the p protons. 

Although steroidal spiro oxiranes are difficult to obtain stereochemically pure by peracid epoxidations of exocyclic methylenes,the recently developed methylene transfer reagents, dimethylsulfonium methylide and di-methylsulfoxonium methylide in tetrahydrofuran, proved useful in the stereoselective transformation of steroid ketones to a- and -oxiranes, (87) and (88), respectively. ... 

Dimethylsulfonium methylide is less stereoselective than dimethylsul-foxonium methylide. 

Dimethyl-5a-cholestan-3-one, 92 Dimethylmagnesium, 86 Dimethylsulfonium methylide, 18, 113 Dioxane dibromide, 220... 

Benzyloxycarbonyloxy)phenyl]dimethylsulfonium methyl sulfate, NaOH, H20,51-95% yield. " This is a water-soluble reagent for benzyloxy carbamate formation. Analogous reagents for the introduction of BOC and Fmoc were also prepared and give the respective derivatives in similar high yields. 

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. 

HOMO of dimethylsulfonium ylide describes the extent to which a 7i bond is present. 

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. ... 

In the initial report by Corey and Chaykovsky, dimethylsulfonium methylide (2) reacted smoothly with benzalaniline to provide an entry to 1,2-diphenylaziridine 67. Franzen and Driesen reported the same reaction with 81% yield for 67. In another example, benzylidene-phenylamine reacted with 2 to produce l-(p-methoxyphenyl)-2-phenylaziridine in 71% yield. The same reaction was also carried out using phase-transfer catalysis conditions.Thus aziridine 68 could be generated consistently in good yield (80-94%). Recently, more complex sulfur ylides have been employed to make more functionalized aziridines, as depicted by the reaction between A -sulfonylimine 69 with diphenylsulfonium 3-(trimethylsilyl)propargylide (70) to afford aziridine 71, along with desilylated aziridine 72. ... 

Recently, in connection with the use of sulfur ylides in polymerization, Kondo and his coworkers [64] attempted to use diphenylsulfonium bis(methoxycarbo-nyl)methylide (DPSY) (Schemes 27, 29) methylphen-ylsulfonium bis-(methoxycarbonyl)methylide (MPSY) (Scheme 30) and dimethylsulfonium bis (methoxycar-bonyl) methylide (DMSY) (Scheme 31) as photoinitiators for the polymerization of MMA and styrene. They concluded that DPSY and MPSY are effective photoini-... 

In the third sequence, the diastereomer with a /i-epoxide at the C2-C3 site was targeted (compound 1, Scheme 6). As we have seen, intermediate 11 is not a viable starting substrate to achieve this objective because it rests comfortably in a conformation that enforces a peripheral attack by an oxidant to give the undesired C2-C3 epoxide (Scheme 4). If, on the other hand, the exocyclic methylene at C-5 was to be introduced before the oxidation reaction, then given the known preference for an s-trans diene conformation, conformer 18a (Scheme 6) would be more populated at equilibrium. The A2 3 olefin diastereoface that is interior and hindered in the context of 18b is exterior and accessible in 18a. Subjection of intermediate 11 to the established three-step olefination sequence gives intermediate 18 in 54% overall yield. On the basis of the rationale put forth above, 18 should exist mainly in conformation 18a. Selective epoxidation of the C2-C3 enone double bond with potassium tm-butylperoxide furnishes a 4 1 mixture of diastereomeric epoxides favoring the desired isomer 19 19 arises from a peripheral attack on the enone double bond by er/-butylper-oxide, and it is easily purified by crystallization. A second peripheral attack on the ketone function of 19 by dimethylsulfonium methylide gives intermediate 20 exclusively, in a yield of 69%. 

The sense of asymmetric induction could be tuned in two ways firstly through the chirality of the sufinyl group, and secondly through the use of dimethylox-osulfonium methylide (n = 1) or of dimethylsulfonium methylide (n = 0), which was found to provide aziridines with opposite diastereoselectivity. This was interpreted by assuming the process to be under thermodynamic control in the former... 

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... 

CN [3-[[4-(3-ethoxy-2-hydroxypropoxy)phenyl]amino]-3-oxopropyl]dimethylsulfonium p-toluenesulfonate... 

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. 

Examples of the use of dimethylsulfonium methylide and dimethylsulfoxonium methylide are listed in Scheme 2.21. Entries 1 to 5 are conversions of carbonyl compounds to epoxides. Entry 6 is an example of cyclopropanation with dimethyl sulfoxonium methylide. Entry 7 compares the stereochemistry of addition of dimethylsulfonium methylide to dimethylsulfoxonium methylide for nornborn-5-en-2-one. The product in Entry 8 was used in a synthesis of a-tocopherol (vitamin E). 

Dimethylsulfonium methylide reacts with reactive alkylating reagents such as allylic and benzylic bromides to give terminal alkenes. A similar reaction occurs with primary alkyl bromides in the presence of Lil. The reaction probably involves alkylation of the ylide, followed by elimination.289... 

The synthesis of S. J. Danishefsky s group is outlined in Scheme 13.55. The starting material is a protected derivative of the Wieland-Miescher ketone. The oxetane ring is formed early in this synthesis. An epoxide is formed using dimethylsulfonium methylide (Step A-3) and opened to an allylic alcohol in Step A-4. The double bond... 

Addition of benzotriazole to l-phenyl-2-aroylacetylenes gives a,/3-unsaturated ketones 221 in high yields. By treatment with dimethylsulfonium ylide, ketones 221 are converted to epoxides 222, Opening of the oxirane ring and electrophilic attack of the obtained tertiary carbocation on N-2 of the benzotriazole system leads to betaines 223 that consecutively eliminate formaldehyde to give triazapentalenes 224 (Scheme 28) <2004ARK(iii)109>. 

Diphenylcyclopropane has been prepared in 24% yield by the Simmons-Smith reaction,2 in 78% yield by treatment of 3,3-diphenylpropyltrimethylammonium iodide with sodium or potassium amide,3 in 61% yield by reaction of 1,1-diphenyl-ethylene with dimethylsulfonium methylide,4 and in unspecified yields from 1,1-diphenylethylene by reaction with diazomethane followed by pyrolysis of the resulting pyrazoline or by reaction with ethyl diazoacetate followed by distillation of the corresponding acid over calcium oxide.5... 

For example, an oxaspirohexane <52, readily available by condensing cyclobutanone 61 with dimethylsulfonium methylide, rapidly rearranges (isomerizes) to the cyclopentanone 63 upon exposure to a catalytic amount of lithium bromide55). The high diastereoselectivity of the initial cyclobutanone formation translates into a high diastereoselectivity for cyclopentanone annulation as this example of Eq. 74 demonstrates. 

Oxidation of p-hydroxy ketones. Reaction of the Corey-Kim reagent with these substrates can result in dimethylsulfonium dicarbonylmethylides in 80-98% yield. These S-ylides are desulfurized to p-diketones by zinc in acetic acid, p-... 

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