Preparation and transformations of allenic ketones and 3(2H)-furanones

Abstract

Swern oxidation of allenic alcohols 7 and 10 gives the corresponding ketones 3 and 12. Reaction of 3 with ruthenium tetroxide yields the stable acyl ketene 17 and the acyloxy α-diketone 20 as well as pivalil (4). Formation of 20 by way of the 3(2H)-furanone 22 is suggested, since oxidation of 3 and 12 with osmium tetroxide followed by dehydration provides the corresponding furanones 22 and 26 in good yield. Epoxidation of 3 furnishes some 20 as well as 27 and 29, the first stable keto allene oxide and bisepoxide, respectively. On thermolysis 27 rearranges to furanone 22. The double bond of 22 is cleaved by peracid to form 20; similar treatment of 31a, b leads to cleavage of the double bond accompanied by Baeyer–Villiger oxidation, with formation of the carboxylic acids corresponding to methyl esters 33a, b as the major products.