Sulfoxides, stereoselective synthesis

Stereoselective Synthesis of )0-Hydroxy Sulfoxides Catalyzed by Cyclohexanone Monooxygenase... 

Functionalization of organic substituents adjacent to the sulfoxide moiety constitutes an important method of synthesis of a variety of sulfoxides which are required for special synthetic purposes or serve as a source of many sulfur-free organic compounds. This section will be mainly devoted to the use of alkylation reactions of sulfinvl anions in stereoselective synthesis and will not review the tremendous amount of work described in the chemical literature without any stereochemical implication. 

Trisubstituted alkenes.9 A stereoselective synthesis of trisubstituted alkenes uses (E)-alkenyl sulfoxides (1)>U as the starting material. These are reduced to the corresponding sulfides (2)," which undergo coupling with Grignard reagents in the presence of complexes of nickel chloride and phosphines as catalyst.12 The products (3) are obtained in steroisomeric purity of > 99%. 

G. Solladie, Formation of C-C Bonds by Addition to Carbonyl Groups (0=0) - Metalated Sulfoxides or Sulfoximides, in Methoden Org. Chem. (Houben-Weyl) 4th ed., 1952, Stereoselective Synthesis (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), Vol. E21b, 1793, Georg Thieme Verlag, Stuttgart, 1995. 

RECENT ADVANCES IN THE STEREOSELECTIVE SYNTHESIS OF CHIRAL SULFOXIDES... 

The preparation of a-selenoketones, esters, nitriles and related compounds can easily be performed via alkylation of the corresponding enolates or stabilized carbanions [21]. These compounds have found many synthetic applications in radical chemistry. In Eq. (9), a typical example involving a ketone is depicted [22]. The stability of a-selenoketones such as 41 is remarkable. Similar reactions with lactones have been performed. For instance, this approach has been applied to the stereoselective synthesis of oxygen-containing rings to either faces of a bicyclic structure [23]. The approach based on a-selenenylation/radical allyla-tion compares favorably with classical enolate allylation procedures, which usually leads to mixture of mono- and diallylated compounds. Furthermore, this strategy is excellent for the preparation of quaternary carbon centers [24] as shown by the conversion of 43 to 45, a key intermediate for the synthesis of fredericamycin A, [Eq. (10)] [25]. Similar reactions with sulfoxides [26] and phosphonates [27] have also been reported. 

Crich and co-workers have demonstrated elegantly that the stereoselective synthesis of fi-mannosides with glycosyl sulfoxides proceeds via anomeric a-triflate intermediates (51). Crich... 

Since the 1,4-y-adducts can be converted to various types of bicyclic compounds, 1,4-addition of allyiic sulfoxides to enones provides a useful tool for stereoselective synthesis of cyclic compounds. Further, the 1,4-addition can be utilized in a three-component coupling process for synthesis of prostanoic acid derivatives (Scheme 20). Typical examples of addition of the Uthio derivative (78) of ( )-allyl p-tolyl sulfoxide to cyclic enones are summarized in Scheme 21. ... 

D. Kahne et al. developed a one-pot multicomponent stereoselective synthesis for the trisaccharide portion of cyclamycin 0 using the Kahne glycosidation.The reactivity of the glycosyl donor was tuned (the rate limiting step is the triflation of the sulfoxide) and the p-methoxyphenyl sulfoxide was activated first. The trisaccharide was obtained in an overall 25% yield with complete a-selectivity. 

Under the same basic conditions /ra . -l-acetoxymethyl-1-methyl-2-tosylcyclopropane generated an a-sulfonyl anion, which attacked the ester group intramolecularly and afforded 2,5-dimethyl-l-tosyl-3-oxabicyclo[3.1.0]hexan-2-ol (22) in 50% yield.Stereoselective synthesis with a chiral cyclopropyl sulfoxide was experienced when ( )-4-tolylsulfinylcyclopropane was reacted first with butyllithium and then with methyl benzoate and gave 1-benzoyl-1-[(5)-4-tolylsulfinyl]cyclopropane (23a) in 62% yield. A useful reaction took place when 2-(hy-droxymethyl)cyclopropyl phenyl sulfide was treated first with an excess of butyllithium and then with dimethylformamide and gave 2-hydroxy-l-phenylsulfanyl-3-oxabicyclo[3.1.0]hexane (24), a lactol which has been used to carry out various useful synthetic transformations. Another useful reaction occurred when cyclopropyl phenyl sulfones were treated with butyllithium followed by an acyl imidazole to give acyl cyclopropanes in decent yield. 

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