Disparate behavior of ketones and thioketones on reaction with organolithiums

Computational Study of the Properties and Reactions of Small Molecules Containing O, S, and Se

“…The reactions of the MeXMe and Me 2 CX compounds with acids of different strengths also are of interest. It is known that the proton affinity of dimethyl ether is smaller than that of dimethyl sulfide, and it appears that the initial complex formed upon reaction of methyllithium with acetone is somewhat more stable than that of thioacetone . Thus, the apparent relative basicities of oxygen and sulfur are reversed from the former pair of reactions to the latter.…”

“…It is known that the proton affinity of dimethyl ether is smaller than that of dimethyl sulfide, 8 and it appears that the initial complex formed upon reaction of methyllithium with acetone is somewhat more stable than that of thioacetone. 2 Thus, the apparent relative basicities of oxygen and sulfur are reversed from the former pair of reactions to the latter. These observations have led us to calculate, using CBS-QB3, the reaction enthalpies and free energies for dimethyl ether, dimethyl sulfide, dimethyl selenide, acetone, thioacetone, and selenoacetone reacting as bases with the following acids: a proton, 15 methyl cation, 16 lithium cation, 17 methyllithium, and methanol.…”

“…For example, the addition of ethanol to phenyl isocyanate is 48 000 times more rapid than is the addition to phenyl isothiocyanate; 1 the reaction of n-butyllithium (n-BuLi) with 2-adamantanone gives the tertiary alcohol as the exclusive product, but the reaction of n-BuLi with 2-adamantanethione gives mainly the reduction product, adamantanethiol. 2 The physical properties of oxygen-containing molecules and their sulfur analogs are also quite different. The CdS bond dissociation energy of thioformaldehyde is nearly 50 kcal/mol smaller than that of formaldehyde; 3 thiocarbonyl compounds have their nÀπ* transitions shifted by ∼2 eV to lower energies than their carbonyl analogues.…”

“…There are significant differences in properties and reactivity between oxygen-containing compounds and their sulfur-containing analogs. For example, the addition of ethanol to phenyl isocyanate is 48 000 times more rapid than is the addition to phenyl isothiocyanate; the reaction of n -butyllithium ( n -BuLi) with 2-adamantanone gives the tertiary alcohol as the exclusive product, but the reaction of n -BuLi with 2-adamantanethione gives mainly the reduction product, adamantanethiol . The physical properties of oxygen-containing molecules and their sulfur analogs are also quite different.…”

Contrasting Reactions of Ketones and Thioketones with Alkyllithiums: A Coordinated Experimental and Computational Investigation

“…Nonetheless, there is no consensus as to the etiology of the contrasting behavior of ketones and thioketones in their reactions with main-group organometallics. In an effort to more fully understand the strikingly different behavior of ketones, which add organolithiums to give tertiary alcohols, and thioketones, which are either reduced by organolithiums to afford secondary thiols or undergo thiophilic addition to deliver sulfides, we have investigated the reactions of a representative aliphatic thioketone, adamantanethione ( 1 ), with a selection of organolithiums and have explored both the addition reactions and the reduction reactions using computational methods …”