Stereoselective preparation of conjugated (Z)-1,3-enynes by dehydration reactions of allenic bromohydrins and the use of the enynes in base-mediated tandem allylation ene-carbocyclization reactions with ß-ketoesters.

A procedure has been developed for the concise, stereoselective synthesis of (Z)-5-bromo-4-aryl-pent-3-en-1-ynes through Sc(OTf)3 catalyzed dehydration reactions of allenic bromohydrins. (Z)-1,3-Enynes are transformed to methylenecyclopentenes when subjected to a sequential, one-pot process involving base mediated allylation reactions with ethyl acetoacetate followed by ene-carbocyclization reactions. An unprecedented rearrangement reaction involving 1,5-acyl migration takes place when the methylenecyclopentenes are treated with acid to form highly substituted cyclopentadienes.

Synthesis of 2-Alkenyl-2H-indazoles from 2-(2-Carbonylmethyl)-2H-indazoles.

A procedure has been developed for synthesis of 2-alkenyl-2H-indazoles starting from 2-(2-carbonylmethyl)-2H-indazoles, which are prepared by gallium/aluminium- and aluminium-mediated, direct, regioselective alkylation of indazoles with α-bromocarbonyl compounds. The structure of 3-(2H-indazol-2-yl)-2H-chromen-2-one was proven by X-ray crystallography. The styrene- and coumarin-2H-indazoles produced by using the new method were found to have interesting fluorescence properties.

Synthesis of hexahydro-1H-isoindole derivatives from arylacyl bromides via homoallenic bromohydrins.

A procedure has been developed for the concise synthesis of hexahydro-1H-isoindole derivatives starting from phenacyl bromides. The approach employs a sequence involving an initial indium-mediated allenylation reaction of an arylacyl bromide with propargyl bromide. This process is followed by FeBr3-mediated SN2'-type substitution reaction of the formed homoallenic bromohydrin to produce a 2,5-dibromo-4-aryl-1,3-pentadiene, which then is subjected to a sequential, one-pot N-alkylation reaction with N-allyl-N-(p-tosyl)amine and a highly diastereoselective intramolecular Diels-Alder reaction of the formed ene-diene to generate the target hexahydro-1H-isoindole.