Noyori Spectroscopy

A more recent isotope study has been conducted with the use of the actual Noyori catalyst by Casey and Johnson [41], They studied the kinetic isotope effect by H NMR spectroscopy at -10 to -30 °C for the reaction of d, d-i (CH/OD and CD/OH), < s isotopically substituted propan-2-ol and 4-phenylbut-3-yn-2-none. The catalyst and the reaction are shown in Figure 4.31. 

The rates for the methylation of cyclopentanone and for the proton abstraction from 2-methylcyclopentanone were significantly increased by a factor of 7500 and 5, respectively, when six equivalents of HMPA were added to the reaction. Using 31P, 7Li and 13C NMR spectroscopy, Suzuki and Noyori found that the tetrasolvated Dy dimer was exclusively generated from the tetrameric (T0,4) and dimeric (D0,4) tetrasolvated lithium amine-free enolate of cyclopentanone (0.16 M in THF, —100 °C, ratio 2/3)275. Kinetic analysis gave a first-order reaction in dimer and HMPA for the reaction with a modulation for free HMPA33, and a first-order reaction in dimer for deprotonation, independent of HMPA. Possible transition state structures for alkylation and proton abstraction are drawn in Scheme 85. 

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