Enol sulfonate esters

Conversion Of Enolates to SUyl Enol Ethers, Silyl Enol Esters, and Silyl Enol Sulfonate Esters... 

Sily enol ether Enol ester Enol sulfonate ester... 

The third procedure illustrated by this preparation involves the reaotion of ketones with trifluoromethanesulfonic anhydride in a solvent such as pentane, methylene chloride, or carbon tetrachloride and in the presence of a base such as pyridine, lutidine, or anhydrous sodium carbonate.7-11,15 This procedure, which presumably involves either acid-catalyzed or base-catalyzed enolization of the ketone followed by acylation of the enol with the acid anhydride, has also been used to prepare other vinyl sulfonate esters such as tosylates12 or methanesulfonates.13... 

The major advantages of this procedure over the enol sulfonate procedure lie in the availability of diethyl 2-chloro-2-cyclopropylethene-l,l-dicarboxylate from the corresponding acylmalonate and phosphorus oxychloride, and the fast, homogeneous, decarboxyl ative elimination reaction of the triethylamine salt of the half-ester in dry organic solvents. The conditions described here, with slight modifications (overnight treatment), have been used for a variety of g-chloro alkyl idene/aryl idene malonates as shown in Table I. 

Complete details for synthesis of ( + )- or ( —)-l from (IS)- or (1R)-10-camphor-sulfonic acid in 77% yield are now available. In general, this oxaziridine is less active than other N-sulfonyloxaziridines, but it is the preferred reagent for hydrox-ylation of lithium enolates of esters, amides, and ketones in 30-95% ee.1... 

A large number of reactions have been presented in this chapter. However, all of these reactions involve an enolate ion (or a related species) acting as a nucleophile (see Table 20.2). This nucleophile reacts with one of the electrophiles discussed in Chapters 8, 18, and 19 (see Table 20.3). The nucleophile can bond to the electrophilic carbon of an alkyl halide (or sulfonate ester) in an SN2 reaction, to the electrophilic carbonyl carbon of an aldehyde or ketone in an addition reaction (an aldol condensation), to the electrophilic carbonyl carbon of an ester in an addition reaction (an ester condensation) or to the electrophilic /3-carbon of an a,/3-unsaturated compound in a conjugate addition (Michael reaction). These possibilities are summarized in the following equations ... 

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). ... 

SnCLrinduced cyclizations between alkenes and enol acetates result in cycloalkanes or bicycloalkanes in high yield (Eq. 59). It is interesting to note that the MesSiOTf-catalyzed reaction can yield fused rather than bicyelo products. Alkenic carboxylic esters, allylic alcohols, sulfones, and sulfonate esters are also cyclized in the presence of SnCU alkenic oxiranes, however, often cyclize in poor yield [89a]. 

In principle, / -diketones may react at the enolic hydroxyl or the a-carbon in practice, in two examples studied both modes of reaction were seen91. Dimedone with phenylmethanesulfonyl chloride and triethylamine yielded the sulfonic ester of the enol, while dibenzoylmethane gave quantitative conversion to the sulfone, (PhC0)2CHS02CH2Ph91. 

By the reaction of the camphor enolate with 1,2-di(chloromethyl)benzene, a borneol derivative 26 with a spiro substituent in position 3 was obtained21 25. It has been used in the form of a sulfonic ester for silylation of carbanions (Section D.9.) and for the enantioselective formation of aminophosphonic acids25. 

Acyl alkoxycarbonyl sulfides Enol sulfonates a,P-Ethylenesulfonic acids a,P-Oxidosulfones a-Sulfinylcarboxylic acid esters 1 -Sulfonylenolethers Ynol tosylates... 

Graphite-potassium Support for reduction of ketones, alkylhalides, alkyl sulfonate esters formation of enolate anions reduction of transition metals Bergbreiter and Killough, 1978 and references therein... 

TBDMS triflate also catalyzes the ene reaction of sulfur dioxide with silyl enol ethers. The silyl sulfinate intermediates can be halogenated to the corresponding sulfonyl halide, and subsequently trapped with an amine or alcohol to give sulfonamides or sulfonate esters, respectively (eq 51). ... 

There have been two general approaches to the direct asymmetric epoxidation of carbonyl-containing compounds (Scheme 1.2) ylide-mediated epoxidation for the construction of aryl and vinyl epoxides, and a-halo enolate epoxidation (Darzens reaction) for the construction of epoxy esters, acids, amides, and sulfones. 

Thus, the dianion derived from a-amino acid substitutes the /1-chloride to give the ester of 2-(phenylsulfonyl)ethenyl amino acid and subsequent desulfonylation provides N-(benzoyl)vinylalanine methyl ester (62) (equation 61). The conjugate addition of enolates to methyl styryl sulfone (63) and subsequent intramolecular addition to the carbonyl moiety provide a synthetically valuable method for the construction of bicyclic and tricyclic skeletons52. Desulfonylation of the cyclization product 64 with sodium in ethanol-THF gives the diene 65 in good yield (equation 62). 

In the first step an S03 molecule is inserted into the ester binding and a mixed anhydride of the sulfuric acid (I) is formed. The anhydride is in a very fast equilibrium with its cyclic enol form (II), whose double bonding is attacked by a second molecule of sulfur trioxide in a fast electrophilic addition (III and IV). In the second slower step, the a-sulfonated anhydride is rearranged into the ester sulfonate and releases one molecule of S03, which in turn sulfonates a new molecule of the fatty acid ester. The real sulfonation agent of the acid ester is not the sulfur trioxide but the initially formed sulfonated anhydride. In their detailed analysis of the different steps and intermediates of the sulfonation reaction, Schmid et al. showed that the mechanism presented by Smith and Stirton [31] is the correct one. 

Other leaving groups are sometimes used. Sulfates, sulfonates, and epoxides give the expected products. Acetals can behave as substrates, one OR group being replaced by ZCHZ in a reaction similar to 10-101. Ortho esters behave similarly, but the product loses R OH to give an enol ether. ... 

---