Sulfoxides, cyclic

Keto Sulfoxides. Cyclic p-keto sulfoxides are readily obtained from the magnesium enolate of the ketone and (—)-menthyl (S)-p-toluenesulfinate as a mixture of diastereomers in which the major epimer has the sulfoxide group in the equatorial orientation (eq 14). 

Platinum square planar complexes Alkenes, allenes, arsines, phosphines, sulfoxides, cyclic ethers, etc. [49,50]... 

Sodium hydride/dimethyl sulfoxide Cyclic y5-amino-a, -ethylenenitriles from ditosylates via dinitriles... 

Dimethyl sulfoxide Cyclic ethers from diols... 

S-heterocyclics 23, 690 pyraii ring, dihydro- 20, 526 sulfoxides, cyclic 23, 586... 

In cyclic sulfoxides Che diastereomeric product ratio is even higher, and the chirality of the sulfur atom has been efficiently transferred to the carbon atom in synthesis. 

The procedure described is an example of a more general synthetic method for the direct conversion of ketones into cyanides. " The reaction has been carried out successfully with acyclic and cyclic aliphatic ketones, including numerous steroidal ketones and aryl-alkyl ketones. The conversion of diaryl or highly hindered ketones such as camphor and )3,j8-dimethyl-a-tetralone requires the use of a more polar solvent. The dimethoxyethane used in the present procedure should be replaced by dimethyl sulfoxide. ... 

The conversion of cyclic sulfides to sulfones is accompbshed by more energetic oxidations. Perhalogenated thiolanes [106] and 1,3-dithietanes [107] are oxidized to sulfones and disulfones, respectively, by a mixture of chromium trioxide and nitric acid (equation 98) The same reagent converts 2,4-dichloro-2,4-bis(tnfluoromethyl)-l,3-dif/u cto cs to disulfone derivatives [107], whereas trifluoromethaneperoxysulfonic acid converts the starting compound to a sul-fone-sulfoxide derivative [2(equation 99). 

Cyclic sulfoxides, lactones, lactams, and other heterocycles as transdermal penetration enhancers 99CLY107. 

Asymmetric induction by sulfoxide is a very attractive feature. Enantiomerically pure cyclic a-sulfonimidoyl carbanions have been prepared (98S919) through base-catalyzed cyclization of the corresponding tosyloxyalkylsulfoximine 87 to 88 followed by deprotonation with BuLi. The alkylation with Mel or BuBr affords the diastereomerically pure sulfoximine 89, showing that the attack of the electrophile at the anionic C-atom occurs, preferentially, from the side of the sulfoximine O-atom independently from the substituent at Ca-carbon. The reaction of cuprates 90 with cyclic a,p-unsaturated ketones 91 was studied but very low asymmetric induction was observed in 92. 

The rearrangement of cyclic sulfoxide 130a, which could be obtained from the corresponding thiolsulfinate 163 (Section III.C.l), was studied in different experimental conditions. The ci3-sulfoxide refluxed in toluene for 24 h gave a 1 1 mixture of the pyrrole 131 and the dihydro-1,4-thiazine 132. 

Nitro ilkenes are gener illy prepared by the subsdnidon reacdon of fi-nirro sulfides and sulfoxides with a variety of carbon nucleophiles via an addidon-eliminadon sequence. This method is partiadarly usefiil for the preparadon of cyclic nitroalkenes fEq. 4.100. ... 

The crystalline phenylboronate derived by similar treatment of methyl a-L-fucopyranoside was shown to possess the 3,4-cyclic structure (25). This assignment is based on oxidation of compound 25 with methyl sulfoxide-acetic anhydride and the chromatographic identification of... 

The reaction is believed to proceed via a six-membered cyclic transition state, analogously to the carbonyl addition of enolates, but the energy differences between boat- and chair-like arrangements are lower for x-sulfinyl carbanions69. Tor tert-butyl sulfoxides only anti- and, vn-products are obtained, arising from the approach onto the same diastereotopic face of the anion, but with different relative topicity. The exchange of lithium by zinc causes an increase of the anft-produci, but attempts to titanate the anion failed (see Table 3)69. 

The addition of a cyclic vinyl sulfoxide anion to aldehydes has been reported only once14. Interestingly, 2,3,4,5-tetrahydro-l//-thiepane S-oxide cannot be metalated by lithium diiso-propylamide in tetrahydrofuran at — 78 °C. At higher temperatures ( — 20° to 0°) a white polymeric precipitate is formed. This polymeric product is also formed when the sulfoxide is treated with butyllithium or. wr-butyllithium in tetrahydrofuran even at — 78 C. However, metalation can be accomplished with. sec-butyllithium using an excess of N,N,N, N -tetramcthylethylenediamine in tetrahydrofuran at —78 C. In this case, a pale yellow solution is formed immediately and upon addition of benzaldehydc instantaneous dccolorization occurs yielding a mixture of diastereomeric alcohols in 90% yield. 

Lithium and zinc tert-butyl phenylmethyl sulfoxide (1) and A-phenyl imines 2, in which the substituent R is alkenyl or aryl, react at —78 °C over 2 hours with high anti diastereoselection (d.r. >98.5 1.5)6. Shorter reaction times result in poorer yields, due to incomplete reaction. In contrast, the reaction of the sulfoxide anion with benzaldehyde is complete after 5 seconds, but shows poor diastereoselection. When the substituent R1 or R2 of the imine 2 is aliphatic, the substrates exhibit poor chemical reactivity and diastereoselection. The high anti diastereoselection suggests that if a chelated cyclic transition state is involved (E configuration of the imine), then the boat transition state 4 is favored over its chair counterpart 5. 

The addition of the anions of racemic cyclic allylic sulfoxides to various substituted 2-cyclopentenones gives y-l,4-adducts as single diastereomeric products22. The modest yields were due to competing proton-transfer reactions between the anion and enone. The stereochemical sense of these reactions is identical to that for the 1,4-addition reaction of (Z)-l-(/erf-butylsulfinyl)-2-methyl-2-butene to 2-cyclopentenone described earlier. 

Only relatively few nucleophilic substitution reactions at sulfur proceed with retention. Oae found that (R)-(+)-methyl p-tolyl sulfoxide exchanged 180 with dimethyl sulfoxide at 150 °C much faster than it racemized thus, the exchange took place with retention. A cyclic intermediate, 136, was proposed to account for this behavior12,147. The same sulfoxide was found to react with N, JV -ditosylsulfurdiimide, 137, with either retention or inversion depending on the reaction conditions. Christensen148 observed retention in benzene whereas Cram and coworkers149 found that inversion took place in pyridine. A four-membered ring intermediate, 138, was postulated to account for the retention, whereas a... 

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