Aggregation and ion pair acidity in THF: lithium and cesium enolates of α-phenylcyclohexanone

Why Is Alkylation of an Enolate Accompanied by So Much Polyalkylation?

“…Three decades ago, however, House conjectured that the explanation could lie in greater aggregation of the less substituted enolate, with the implied assumption that the more highly aggregated enolate is less reactive. To our knowledge no definitive test of this hypothesis has ever been published, but it is consistent with recent quantitative studies of the aggregation and reactivity of lithium and cesium enolates in THF, which show that the monomers are generally more reactive than the dimer or tetramer aggregates in alkylation reactions . In this paper we provide a definitive test with aggregation equilibrium constants and benzylation rates for the lithium enolates ( 1-Li and 2-Li ) of 6-phenyl-α-tetralone, 1 , and 2-benzyl-6-phenyl-α-tetralone, 2 .…”

“…LiPAT, 1-Li , was measured against two indicators, 11-phenylbenzo[ c ]fluorene (Ph-3,4-BF, p K = 14.84) 6 and 1,2,3-triphenylindene (TPI, p K = 14.97); the experimental details for four runs are summarized in Table S3 (Supporting Information). The data fit eq 7 (Figure ) and give average values for 1-Li of p K 0 = 14.22 ± 0.04 and K 1,4 = (4.7 ± 0.5)E+10 M -3 in which p K 0 refers to the monomeric enolate and K 1,4 = [tetramer]/[monomer] 1 Plots of four proton-transfer runs with two indicators (×, TPI; ◊, □, and ○, Ph-3,4-BF).…”

“…6-Phenyl-α-tetralone came from another study 4f. The α-benzyl ketone, 2 , was prepared 5 by treatment of the magnesium salt with benzyl bromide, and the dibenzyl ketone, 3 , was prepared by treatment of 2 with benzyl bromide (Supporting Information).…”

Aggregation and Reactivity of the Cesium Enolate of 6-Phenyl-α-tetralone: Comparison with the Lithium Enolate1

“…The variation in λ max is too small for application of singular value decomposition, an analysis applied in several previous examples of enolate aggregation. ,− Thus, we could use only the method of coupled equilibria for determining the aggregation equilibrium constants; however, the presence of an isosbestic point for CsPAT shows that only two components are present. A similar isosbestic point had been found for LiPAT.…”

“…In recent papers, we have described the aggregation and reactivity of the lithium and cesium enolates of several ketones: p -phenylisobutyrophenone, LiPhIBP and CsPhIBP, 2-phenylcyclohexanone, LiPCH and CsPCH, 2-( p -biphenylyl)cyclohexanone, LiBPCH and CsBPCH, 2,6-diphenyl-α-tetralone, LiPhPAT and CsPhPAT, and the lithium enolates of p -phenylsulfonylisobutyrophenone, LiSIBP, 6-phenyl-α-tetralone, LiPAT, and 2-benzyl-6-phenyl-α-tetralone, LiBnPAT . In the present paper, we extend the study to the cesium enolate, CsPAT, of 6-phenyl-α-tetralone, PAT.…”