Oxidative Seco Rearrangement. A Novel Carbon-Carbon Bond Cleavage

Article abstract of DOI:10.1021/jo01298a018

Cycloalkanones can be converted to 2,2-(trimethylenedithio)cycloalkanones and, by reduction or addition of an organometallic reagent, to the corresponding alcohols.These hydroxydithianes undergo a novel ring cleavage with concomitant rearrangement of the oxidation pattern to produce 3-(ω-oxoalkyl)-1,4-dithiacycloheptan-2-ones upon treatment with lead tetraacetate.In this way the oxidation level of C(1), C(2), and C(3) of the original cycloalkanone has been adjusted.Six-, nine-, and twelve-membered rings have been cleaved in 65-95percent yields.The regiocontrol of the method was illustrated with a 2- and a 3-substituted cyclohexanone in which only the oxidation pattern of C(5), C(6), and C(1) were adjusted.The 1,4-dithiacycloheptan-2-ones are simultaneously a β-keto sulfide and a thioester.The β-keto sulfide was subjected to oxidation-elimination to illustrate the versatility of these substances, giving (after methanolysis) pure (E)-α,β-unsaturated methyl esters.This process extended the adjustment of the oxidation level to C(4) of the original cycloalkanone.Application of this sequence to cyclononanone allowed a synthesis of the queen's substance that is found in several species of insects.The utility of the thioester unit was illustrated by a ketone synthesis upon treatment with organocuprates.The resultant α-thioketones were subjected to oxidation-elimination to give (E)-α,β-unsaturated enones.Possible mechanistic pathways for this unusual oxidative rearrangement are discussed.In this connection, it was found that treatment of a ketene thioacetal with lead tetraacetate at 55 deg C smoothly effected acetoxylation.