Enol sulfonates

Methanesulfonyl chloride reacts with enamino ketones (104), (e.g., 151) to give good yields of the enol sulfones (e.g., 152). The analogy with ketene addition to form a-pyrones (Section IV.A) is obvious. 

Reactions of vinylogous amides with methanesulfonyl chloride also led to the formation of six-membered rings. Here the initial attack on oxygen produces a zwitterionic intermediate which can collapse to an enol sulfonic acid lactone (383,469). 

In connection with route A, the formation of sulfones from sulfinates and a-haloketones on the one hand, and of isomeric enol sulfonates on the other (cf. Section III. A.4), should be pointed out. 

Unfortunately, it quickly became apparent that a shortfall in this proposal was an inability to prepare the desired vinyl halide 25 in a straightforward and selective manner [19]. In contrast, we reasoned that the selective formation of an enol sulfonate, such as the enol triflate 26a, could be controlled by judicious tuning of enolization conditions starting from the corresponding ketone, and that such an enol sulfonate would possibly be a substrate for a palladium-mediated coupling (Scheme 9.17). In this way a common intermediate from the previously defined synthesis, that is, the racemic ketone rac-13 or its cyano equivalent rac-5 could be used to generate the required enamide. 

Scheme 9.17 Proposal to prepare and couple an enol sulfonate.

Substituted cyclopropyl rings conjugated with a triple bond system have recently received attention as C5 building blocks. The procedure described here is a modification of the decarboxylation-elimination reaction for the preparation of a.3 acetylenic acids from enol sulfonates of acyl malonates. Addition of aqueous alkali to the enol sulfonate of diethyl cyclopropyl carbonyl malonate gives cycl opropyl propiol ic acid, but the yield is 1 ow. 

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. 

Enol sulfonates. Sulfonylation of enolate anions with 1 is markedly affected by the gegenion. Lithium enolates undergo mainly C-sulfonylation. Cesium or quaternary ammonium enolates undergo regioselective O-sulfonylation. The same behavior is observed with nonailuorobutanesulfonyl fluoride.1... 

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

Sily enol ether Enol ester Enol sulfonate ester... 

Enol Ethers, Enol Carboxylates, Enol Phosphates and Enol Sulfonates... 

Z)-P-Acyloxy-a-fluoroacrylaldehydes. After generation from the fluorinated enol sulfonate the sodium salt of this aldehyde reacts with acid chlorides to provide the substituted acroleins. 

Benzoyl peroxide Ketosulfones from enol sulfonates Radical rearrangement... 

Acyl alkoxycarbonyl sulfides Enol sulfonates a,/3-Oxidosulfones... 

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

Ring closure with enol sulfonates Thianaphthenes... 

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