When Ethyl Is Infinitely Different from Methyl: Double Addition of Lithiated Dithianes to Aromatic Carboxylates Revisited

Abstract

Addition of lithiated alkyl dithianes to benzoyl chloride or methyl benzoate does not produce the expected product of double addition, α,α-bis(alkyldithianyl) benzyl alcohol, for alkyls larger than methyl. Instead, the first step intermediate, i.e. 2-benzoylated dithiane, undergoes an electron-transfer reduction by the second molecule of the dithianyl anion. This reduction is followed by the ring-opening mesolytic fragmentation of the dithiane ring in the ketyl anion radical and subsequent radical recombination yielding acetophenone-tethered thioortho esters 4, α-[3-(2-alkyl-1,3-dithiane-2-ylthio)propylthio]-α-alkyl-acetophenones. It appears that the Corey−Seebach bisaddition of lithiated dithianes to methyl benzoate is an exception rather than the rule in the alkyl dithiane series.