Lithiated 2-alkynyl-1,3-dioxanes as fully oxygenated acyl-anion equivalents Synthesis of 1-alkynyl ketones

Abstract

2-Lithio-2-(trimethylsilylethynyl)-1,3-dioxane 3 is prepared from 2-(trimethylsilylethynyl)-1,3-dioxane with n-BuLi. Alkylation of 3 produces propargylic ketals 2 exclusively. Reaction with group IV-B chlorotrimethylimetalanes gives both propargylic products 2 and allenes 6 depending on the solvent used. Desilylation of 2 as well as hydrolysis to the alkynyl ketones 1 can be carried out under mild conditions. The first 1-alkynyl stannyl ketone has been prepared in this way. Formation of 2-lithio-2-(3,3-dimethyl-1-butynyl)-1,3-dioxane 10 requires t-BuLi. With various electrophiles 10 yields propargylic products and/or allenes in ratios depending on the solvent used.