LICKOR-PROMOTED 1,2-ELIMINATION IN 1,1-DIMETHOXY-2-PHENYLETHANE AND 1,1-DIMETHOXY-2-PHENYLPROPANE - SYNTHESIS OF SUBSTITUTED ENOL ETHERS AND ALKYNES

Dimethyl acetals of phenylacetaldehyde 1a and 2-phenylpropionaldehyde 1b, upon treatment with 1.25 equiv. of LICKOR reagent, undergo 1,2-eli mination (THF at -95 OC) promoted by metallation at the benzylic site, and afford the corresponding enol ethers in the E-form. When the subs trate is treated with an excess of the base (2.5 equiv,), further hydr ogen-metal exchange takes place at the alpha vinyl site of the elimina tion product, and carbonyl electrophiles can be added to the carbanion ic intermediate yielding allyl alcohols, Experimental procedures are g iven for the conversion of the alpha-substituted derivatives into carb onyl compounds, according to an inverse polarity approach. Moreover, a llyl alcohols synthesised starting from acetal 1a, can be transformed into prop-2-ynyl alcohols by treatment with LICKOR base.