Electrophilic cyclization of an olefinic β-keto ester

Abstract

Benzeneselenenyl chloride and aluminum chloride or benzenesulphenyl chloride and silica gel initiate an electrophilic cyclization of methyl 7-methyl-3-oxo-7-octenoate to cyclohexyl derivatives. These products of the cyclization reaction have been converted into intermediates of potential use in the synthesis of unusual carotenoids.

Synthesis of Cyclic Enol Ethers from Alkenyl-β-dicarbonyl Compounds

“…The β-keto esters 8 and 17 gave a complex mixture of products. The reaction of 18 with phenylselenenyl chloride has already been reported in the literature . Using acetonitrile or dichloromethane as solvent, the authors obtained a mixture containing predominantly the product of addition to the double bond, while running the reaction in the presence of aluminum trichloride afforded the C-cyclization product in 84% yield.…”

An expedient approach to carbocycle annulation via silver ion assisted episulphonium ion cyclizations

“…The substrates used in this study, (5a) and (5b), were prepared by the lithiation of (3,4-dimethoxyphenyl)acetonitrile (4) with lithium di-isopropylamide (LDA) followed by alkylation with the appropriate allylic halide.+ Two approaches are currently available for the generation of characterizable episulphonium ions. The first involves the sequential treatment of an appropriate alkene [e.g., (6)] with a sulphefiyl halide followed by exposure of the resultant adduct (7) to silver tetrafluoroborate.2 Alternatively, direct exposure of the alkene (6) to the preformed sulphenium derivative (9) has been reported to give rise to the corresponding episulphonium cation ( 8 ) .…”