Sulfonic esters, vinyl, addition

Vinyl trifluoromethanesulfonates (triflates) are a new class of compounds, unknown before 1969, that have been used most extensively in solvolytic studies to generate vinyl cations.2,3,812 Three methods have been used to prepare these sulfonic esters. The first, involving the preparation and decomposition of acyltriazines,4 requires several steps to prepare the acyltriazines and is limited to the preparation of fully substituted vinyl triflates. The second method involves the electrophilic addition of trifluoromethanesulfonic acid to acetylenes5,8,15 and, consequently, is not applicable to the preparation of trisubstituted vinyl triflates and certain cyclic vinyl triflates. However, this second procedure is relatively simple and often gives purer products in higher yield than the subsequently discussed reaction with ketones. Table I lists vinyl triflates that have been prepared by this procedure. ... 

Aryl and vinyl sulfonate esters are reactive toward oxidative addition, and the perfluoroaUcyl versions are useful substrates in the Heck reaction. Conditions can be mild, comparable to those for vinyl iodide reactions. The enol (vinyl) triflates are particularly attractive, since they are prepared directly from the corresponding ketone (equation 21). ... 

The traditional scope for this reaction involved coupling alkenyl or aryl iodides or bromides with aryl, alkenyl, or alkynylzinc halides. However, recent modifications have allowed the scope to be extended to include additional electrophiles see Electrophile) such as aryl and vinyl chlorides, sulfonate esters, aryl ethers, and substrates with... 

Presently, many organic additives fall into the category of polymerizable monomers. A non-exhaustive list includes esters (including carboxylic esters/carbonates and other inorganic esters such as phosphates, sulfates, and silicates) that are derived from vinyl and allyl alcohols [2,54,71], vinyl pyridine [63], acrylic acid nitrile [110], maleic acid derivatives [125, 131], vinyl sulfones [128], vinyl silanes [113], and isocyanates [65, 171] (Fig. 2). The synergistic effect of different unsaturated compounds used in various combinations has also been reported [1]. 

The enamines derived from cyclic ketones give the normal alkylated products, although there is some evidence that unstable cycloadducts are initially formed (55b). Thus the enamine (28) derived from cyclohexanone and pyrrolidine on reaction with acrylonitrile, acrylate esters, or phenyl vinyl sulfone gave the 2-alkylated cyclohexanones (63) on hydrolysis of the intermediates (31,32,55,56). These additions are sensitive to the polarity of the solvent. Thus (28) in benzene or dioxane gave an 80% yield of the... 

An example for synthesis of the chiral [l-keto ester 69 is illustrated in equation 64. It involves conjugate addition of the dipotassium / -keto ester 68 to vinyl sulfone 67 followed by in situ quenching with allyl bromide54. The method provides a new procedure to sevenring annulation product 70 that is a potential precursor for (l)-(-)-cytochalasin C. 

Recent synthetic applications of the photochemical [2 + 2] cycloaddition of unsaturated sulfones have been noted. Musser and Fuchs84 have effected an intramolecular [2 + 2] addition of a 6-membered ring vinyl sulfone and a five-membered ring vinylogous ester in excellent yield, as part of a synthetic approach to the synthesis of the mould metabolite, cytochalasin C. The stereospecificity of the addition was only moderate, however, and later problems with this synthetic approach led to its abandonment. Williams and coworkers85 have used the facile [2 + 2] photoaddition of 73 and... 

In a like manner, vinyl sulfoxides and sulfones can serve as the equivalents of vinyl and alkenyl cations via a process involving a Michael addition followed by an elimination.43 For example, addition of the enolate of the P-keto ester (168 Scheme 24) to phenyl vinyl sulfoxide (169) furnished, in 50% yield. 

The addition products (27) formed from the same photolytic treatment of O-acyl esters (2) with phenyl vinyl sulfone, can be converted to various kinds of compounds (24), (26), and (28) to (34), as shown in eq. 8.15, and this method really becomes valuable chemistry. 

Generally, treatment with electron-deficient olefins such as nitroethylene or vinyl sulfone is effective for radical addition reactions, since alkyl radicals derived from O-acyl esters (2) are nucleophilic and take SOMO-LUMO interaction. However, treatment of O-acyl esters ) derived from perfluoroalkyl carboxylic acids (RfC02H) generates electrophilic radicals, Rf, which react preferably with electron-rich olefins such as vinyl ether, as shown in eq. 8.16 [52]. 

A similar reaction has been adopted for the preparation of amides from alkenes by the photoaddition of "CONH2 radicals generated from formamide by benzophe-none [7], or via a TBADT [25] photocatalyzed hydrogen abstraction. Solar light has been used in the first case. Furthermore, the introduction of an ester function has been accomplished by generating an alkoxycarbonyl radical by photolysis of [bis(alkoxyoxalyloxy)iodo]benzene at 0-5 °C and ensuing addition to vinyl sulfones in the presence of 1,4-cyclohexadiene [9]. 

Acceptor-substituted alkenes that are employed as substrates in Michael additions include a./l-unsaturated ketones (for example, see Figure 10.59), a,/3-unsaturated esters (Figure 10.60), and a,/3-unsaturatcd nitriles (Figure 10.61). The corresponding reaction products are bifunctional compounds with C=0 and/or C=N bonds in positions 1 and 5. Analogous reaction conditions allow Michael additions to vinyl sulfones or nitroalkenes. These reactions lead to sulfones and nitro compounds that carry a C=0 and/or a O N bond at the C4 carbon. 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, 5 which are very useful synthetic Intermediates. They react with a variety of electrophiles such as carbon dioxide,5,6 epoxides,5,6 aldehydes,6 allylic halides,7 alkyl halides,7 and acetylenic halides 7 they undergo conjugate addition to a,6-unsaturated esters,5 6 ketones,6 aldehydes,6 and sulfones.8 Finally they add smoothly to activated triple bonds6 such as HCSC-OEt, HC3C-SEt, HC=C-CH(0Et)2. In most cases these cuprates transfer both alkenyl groups. The uses and applications of the carbocupration reaction have been reviewed recently.9 The configurational purity in the final product 1s at least 99.951 Z in the above transformations. 

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