作者:Andreas Weichert、H. Martin R. Hoffmann
DOI:10.1021/jo00013a007
日期:1991.6
Modified Jones oxidation of 2-(benzenesulfonyl)-2-alken-1-ols and rapid nonnucleophilic workup below 0-degrees-C yields a variety of alpha-methylene-beta-keto sulfones 4, including crystalline parent 4a and also e-h, which can be stored at -20-degrees-C without change. In the absence of nucleophiles, the new compounds are stable (heating in benzene) toward dimerization and polymerization. Thus, selective cross-reactions are feasible. With alcohols, including sterically hindered tertiary alcohols and also with 2-(ethoxycarbonyl)cyclopentanone, the compounds function as efficient Micheal acceptors, even in the absence of base catalysis. In moist ether, 2-(benzenesulfonyl)-1-penten-3-one (4b) suffers rearrangement to 2-(benzenesulfonyl)ethyl propanoate (9). Sulfonylated alcohol 7 and strained alpha-hydroxyoxetane 8 are assumed as intermediates. Toward electron-rich aromatics and heteroaromatics, alpha-methylene-beta-keto sulfones 4 behave as electrophiles in Friedel-Crafts-type functionalizations. The new compounds are also dienophilic: of the two groups (acetyl and benzenesulfonyl) attached to the ethylenic terminus in 4a, benzenesulfonyl has been found to preferentially adopt the endo position in cycloadditions of cyclopentadiene and also cyclohexadiene. Prototype 3-(benzenesulfonyl)-3-buten-2-one (4a) is a crystalline methyl vinyl ketone (MVK) equivalent which, unlike MVK, undergoes controlled free-radical additions with nucleophilic radicals. In hetero-Diels-Alder reactions, 4a serves as a 1-oxa-1,3-butadiene unit, combining with a wide range of alkenes of graded nucleophilicity. Electron deficient 4a also reacts as an enophile toward 1,1-dialkylated ethylenes. In the presence of ZnCl2.OEt2, the ene reaction with beta-piene can be suppressed completely in favor of cycloaddition, giving a robustadial building block in 85% yield. In further applications to natural products chemistry, the synthesis of frontalin and novel oxatricyclics are described.