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Regioselectivities in Michael-type reactions of organoaluminium and organotitanium reagents with sterically hindered carbonyl compounds 1 and 5 concerning 1,2- versus 1,4-addition were determined. Throughout this investigation Me3Al/cat. Ni(acac)2 was found to be the most useful reagent for strongly hindered systems.

The Michael-type reaction of copper-catalyzed trialkylaluminium reagents with α,β-unsaturated carbonyl compounds is a useful and simple procedure for the transfer of hydrocarbon substituents. The scope of this process and the effect of chlorotrimethylsilane as additive were investigated. Preparatively useful results were generally obtained for enones even with higher organoaluminium reagents, whereas the reaction with α,β-unsaturated aldehydes was limited to the use of trimethylaluminium.

The effect of silanes as additives in the copper-catalyzed conjugate alkylation of enones by various organoaluminium reagents was investigated. TMSCl led to significant lower amounts of CuBr catalyst needed in the reaction of trimethylaluminium with enones, but was unsuccessful in the case of organoaluminium compounds of the formula Me 2 AlY (Y = Cl, OR). Me 2 AlOEt turned out to be a useful reagent for methylation without support of additives.

The conjugate methylation of α,β-unsaturated ketones with trimethylaluminium occurs smoothly in a very simple procedure under the catalytic effect of Cu1 salts. Scope and limitations of this process as well as the influence of solvent and catalyst on the kinetics were studied. In addition, the effect of chlorotrimethylsilane as an additive was investigated. Attack on the carbonyl group in 1,2-fashion could not be observed under the reaction conditions.

The 1,4-addition of organotitanium ate complexes to enones by nickel catalysis is reported. With a methyltitanium ate complex good yields of conjugate addition to sterically hindered enones are achieved. Phenyltitanium ate complexes react with less sterically encumbered enones to the 1,4-addition products in moderate to high yields.

The effect of silanes as additives in the copper-catalyzed conjugate alkylation of enones by various organoaluminium reagents was investigated. TMSCl led to significant lower amounts of CuBr catalyst needed in the reaction of trimethylaluminium with enones, but was unsuccessful in the case of organoaluminium compounds of the formula Me 2 AlY (Y = Cl, OR). Me 2 AlOEt turned out to be a useful reagent for methylation without support of additives.

A very efficient and simple route to bicyclic ketones using propargylic silanes is described. The cyclization is initiated by a trace of Amberlyst 15 that is added to a reaction vessel. Stirring at room temperature and non-aqueous work-up yielded several bicyclic ketones in high chemical yields containing the synthetically very useful terminal allene.

Mixed ketene acetals of type 2 undergo smooth cyclization upon treatment with silica gel yielding diastereoselectively bicyclo[2.2.2]octanones of type 3. Alternatively, the same result was obtained by exposure of the substrates to TiCl4 at low temperature.

The 3-methoxy-2-cyclohexenones (I) react consecutively with LDA, methyl acrylate (II), and trimethylsilyl chloride (III) to form the ketene acetals (IV) which are desilylated and cyclized in the presence of SiO2 or TiCl4, yielding the bicyclic esters (V).