Aggregation and Alkylation of Enolates of 2-Phenyl-α-tetralone and 2,6-Diphenyl-α-tetralone1

Abstract

The cesium (1-Cs, CsPhPAT) and lithium (1-Li, LiPhPAT) enolates of 2,6-diphenyl-α-tetralone, 1, and the lithium enolate (2-Li, LiPhAT) of 2-phenyl-α-tetralone, 2, are present in dilute THF solution as monomers and dimers with K1,2 = 1810 (1-Cs, CsPhPAT), 2650 (1-Li, LiPhPAT), and 1930 (2-Li, LiPhAT) M-1. These values were obtained by singular value decomposition analysis of the UV spectra and by the dependence of ion pair pK's with concentration. On the ion pair pK scales previously defined, the monomers have pK = 17.80 (1-Cs, CsPhPAT) and 11.14 (1-Li, LiPhPAT). The monomers are much faster than dimers in alkylation reactions; reaction products from alkyl halides are those of C-alkylation, but 1-Cs (CsPhPAT) with methyl sulfonates gives large amounts of O-alkylation. Comparison with previous results shows that the reactivity of cesium enolates parallels their basicity but that lithium enolates show no correlation between ion pair pK and alkylation reactivity.