Stereoselectivity vinyl sulfone

The stereoselective conjugate addition of lithium (Z)-dialkenylcuprates to vinyl sulfones gives (Z)-olefms in the range of 70-80% overall yield and no ( )-isomer is detected (equation 66)56. The degree of stereoselectivity is higher than 90%. 

Free-radical addition of Se-phenyl areneselenosulfonates to acetylenes is also a facile process, occurring regiospecifically and stereoselectively to afford the E-isomer of a -(phenylseleno) vinyl sulfone (26) in high yield88. 

Cycloadditions of nitrones, nitrile oxides or diazo compounds to thiete dioxides do not show the high stereoselectivity observed with acyclic vinyl sulfones, and mixtures of the two possible adducts are formed . The charge-transfer stabilization energy calculated according to the Klopman-Salem perturbational approach is able to account for the experimental trends of the isomer ratio in terms of the major stereochemical structural differences between the acyclic vinyl sulfones and the four-membered ring sulfones (see Section IV.B.3). 

Finally, useful stereoselectivities have been recorded for the heteroconjugate addition of organometallic reagents to 1-silyl substituted vinyl sulfones.22 The synthesis of such sulfones can be achieved starting from phenylthioacetylene.6 1 11 23 The synthesis of the dicobalt hexacarbonyl complex24 and the polymerization of phenylthioacetylene25 have been described. 

Another total synthesis of pamamycin-607 (lb) was reported in 2001 by our own group [6] at about the same time as the Lee synthesis. Here, the approach was based on the stereoselective intramolecular Diels-Alder reaction of vinyl-sulfonates and novel methods for elaboration of the resulting sultones [13,14]. 

The reactions of vinyl sulfones with various nucleophiles are usually stereoselective. Substituted vinyl sulfones are less reactive toward nucleophiles than the analogous vinyl ketones or esters 10 and are quite inert toward thiols. Peptide vinyl sulfones do not react with thiols such as glutathione under enzyme assay conditions. The reaction of thiols with aryl vinyl sulfones has been reported, however, it is performed in the presence of base. 11 ... 

Regio- and stereoselective toluenesulfonyl bromide-mediated radical cyclization of bis(allene) (201) in the presence of AIBN also goes ahead to give rise to the transfused 5-membered ring (202) containing vinyl sulfone and vinyl bromide as shown in eq. 3.78. 

A sugar-derived vinyl sulfone (92) was found to undergo a Michael-initiated ring closure (MIRC) process to build up a chiral polysubstituted oxolan system with high stereoselectivity, yielding the all-syn stereoisomer (93) (Scheme 25).61 The observed MIRC selectivity demonstrates that the 5-exo-trig process is strongly... 

During the past two decades, the asymmetric Diels-Alder reaction has become one of the most powerful tools in asymmetric synthesis as a result of its capacity to create up to four chiral centers in one step, often in a highly stereoselective manner. In the following sections, recent advances in this area using vinyl sulfoxide and vinyl sulfone dienophiles will be considered. It should be noted that, although beyond the scope of this review, many asymmetric Diels-Alder reactions of chiral sulfinyl-1,3-dienes have been reported.111... 

Vinyl sulfones. The anion of 1 (n-BuLi) undergoes a Peterson reaction with aldehydes or ketones to afford vinyl sulfones directly in 50-85% yield. Use of dimethoxy-ethane as solvent is essential for satisfactory results. The reaction is not stereoselective. 

Another frequent use of (1) and its enantiomer is the stereospecific conjugate addition of carbonyl compounds to a,p-unsaturated systems. Most published examples contain chiral imine derivatives of cyclic ketones, which add to a,p-unsaturated esters and ketones in a highly stereoselective manner (eq 13 and eq 14). When the ketone is not symmetrically substituted, reaction usually occurs at the most substituted a-position, including those cases where the ketone is a-substituted by oxygen (eq 15). High stereoselectivity can also be achieved when the Michael acceptor is other than an unsaturated ketone or ester, such as a vinyl sulfone (eq 16). Intramolecular variations of this transformation have also been described (eq 17). ... 

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