The scope of the enantioselective palladium-catalyzed allylic alkylation1 can be extended considerably if nonstabilized preformed enolates will function as nucleophiles. We and others elaborated protocols for the asymmetric allylic alkylation of ketone enolates.2,3 Here, we report the diastereoselective and/or enantioselective allylation of nonstabilized lithium enolates derived from lactones.4 The presence of lithium chloride is crucial to reactivity and selectivity.For the allylation of ketone enolates, we have proven an outer-sphere mechanism. A computational study on the allylation of lactones reveals a mechanism wherein lithium chloride plays a key role as the connecting link between the noble metal and the enolate. The observed stereoselectivity agrees perfectly with the results of the theoretical calculations. The transition state based upon DFT calculations is shown in Figure 1 (right).[1] B. M. Trost, M. L. Crawley, Chem. Rev. 2003  , 103, 2921.[2] M. Braun, T. Meier, Synlett 2006  , 661; M. Braun, T. Meier, Angew. Chem. Int. Ed. 2006  , 45, 6952.[3] M. Braun, F. Laicher, T. Meier, Angew. Chem. Int. Ed. 2000  , 39, 3494; M. Braun, T. Meier, F. Laicher, P. Meletis, M. Fidan, Adv. Synth. Catal. 2008  , 350, 303. M. Braun, P. Meletis, M. Fidan, Org. Synth. 2009  , 86, 47.[4] P. Meletis, M. Patil, W. Thiel, W. Frank, M. Braun, Chem. Eur. J. 2011  , 17, 11243.

Stereoselective palladium-catalyzed allylic alkylation of preformed lithium enolates of lactones: Evidence for an outer-sphere mechanism

248th National Meeting (2014)

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