Intercalation of multiple carbon atoms between the carbonyls of alpha-diketones

The reaction of open-chain or cyclic alpha -diketones with specific omega - alkenyl organometallics leads readily under the proper conditions to 1,2-di ols bonded to terminal olefinic chains. With 1-phenyl-1,2-propanedione, bia cetyl, and cyclohexane-1,2-dione, allylindation in aqueous THF proceeds rea dily at both adjacent carbonyls. For cyclododecane-1,2-dione, recourse must be made to allylmagnesium bromide for completing the second-stage condensa tion. Grignard reagents have also served well as reactants for biacetyl mon oadducts. In contrast, monoallylated camphorquinone is reluctant to couple to Grignard reagents and reacts only when Barbier-type alkyllithium reactio ns are applied. The ring closing metatheses. of these products have been ex amined. Where six-membered ring formation operates, cyclization can be perf ormed directly on diols. When larger rings are involved, the diols will rea ct only if structural preorganization capable of facilitating mutual approa ch of the two double bonds is at play. For this purpose, the prior conversi on to a cyclic carbonate holds considerable utility. In the latter setting, saponification must precede the diol cleavage step which has been performe d with lead tetraacetate. The latter reagent also exhibits the very benefic ial effect of facilitating removal of ruthenium and phosphorus byproducts g enerated during the metathesis step. This chemistry conveniently lends itse lf to the controlled intercalation of multiple methylene groups between the carbonyl carbons of readily available a-diketones to deliver linear or cyc lic products.