The employment of hexane/TMEDA dramatically hampers racemization of those lithiated styrene oxides (trifluoromethyl-, chloro-, and thiophenyl-substituted) which have been proven to be configurationally unstable in THF on the time scale of their reactions. The barriers to inversion and the activation parameters calculated (Eyring equation) for reactions run in THF, THF/TMEDA, and hexane/TMEDA suggest the intervention of peculiar eantiomerization mechanisms for each case. The role of TMEDA in both coordinating and non-coordinating solvents has also been questioned and discussed in light of the kinetic data gathered, and a model of deprotonation in hexane/TMEDA has also been proposed. The synthetic benefits of our results became apparent by setting up an asymmetric synthesis of an industrially relevant antifungal agent.
Solvent and TMEDA Effects on the Configurational Stability of Chiral Lithiated Aryloxiranes
PERNA, FILIPPO;Salomone, A;CAPRIATI, Vito
2011-01-01
Abstract
The employment of hexane/TMEDA dramatically hampers racemization of those lithiated styrene oxides (trifluoromethyl-, chloro-, and thiophenyl-substituted) which have been proven to be configurationally unstable in THF on the time scale of their reactions. The barriers to inversion and the activation parameters calculated (Eyring equation) for reactions run in THF, THF/TMEDA, and hexane/TMEDA suggest the intervention of peculiar eantiomerization mechanisms for each case. The role of TMEDA in both coordinating and non-coordinating solvents has also been questioned and discussed in light of the kinetic data gathered, and a model of deprotonation in hexane/TMEDA has also been proposed. The synthetic benefits of our results became apparent by setting up an asymmetric synthesis of an industrially relevant antifungal agent.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
