The chemistry of organoborates. 9. A regiospecific and highly stereoselective construction of trisubstituted αβ-unsaturated ketones, tetrasubstituted αβ-unsaturated ketones and specifically protected 1,3-diketones from alkynyltrialkylborates☆

Abstract Lithium alkynyltrialkyborates react with dioxolanium fluorosulphonates in a highly stereoselective fashion such that the dioxolanium group and the migrating group are on the same side of the new alkene intermediate. Hydrolysis of the intermediate yields Z-trisubstituted αβ-unsaturated ketones in which all three substituents have different origins and can be independently varied. Oxidation of the intermediates gives β-ketoacetals, which are regiospecifically protected 1,3-diketones. If the initial intermediates are allowed to stand, then another migration occurs and tetra-substituted αβ-unsaturated ketones result.