Propargyl dynamic kinetic asymmetric transformation

Scheme 9.31 Gold(l)-catalyzed dynamic kinetic asymmetric transformation of propargyl esters according to Toste and coworkers [58].

Toste s group made several modifications of bis(HBHC)-digold complex 40 by placing differently substituted aryl groups at the binaphthyl 3,3 -positions of the diamine synthon and examined them in catalytic dynamic kinetic asymmetric transformations of propargyl esters (Scheme 16.14) [29b]. Drastic substituent effects on enantioselectivity were observed, with j -trifluoromethylphenyl-... 

Recently, Lin et al. demonstrated that the propargyl alcohol could participate in such a transformation for the synthesis of chiral dihydrofurans [53]. The reaction began with a challenging oxa-Michael addition to cinnamaldehyde derivatives, which was followed by a secondary amine/Pd complex-catalyzed nucleophilic addition/ isomerization of the alkyne moiety in excellent yields and enantioseleclivities (Scheme 9.58). Since the oxa-Michael addition of propargyl alcohol to 0[,P-unsaturated aldehydes was a slow process, this cascade reaction proceeded through a dynamic kinetic asymmetric transformation (DYKAT) process, whereby it made the overall reaction proceed efficiently and with high stereocontrol using the second reaction with precise stereocontrol to shift the first reversible oxa-Michael addition selectively. 

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