Mechanistic Studies of the TRIP-Catalyzed Allylation with Organozinc Reagents.

ABSTRACT

3,3-Bis(2,4,6-triisopropylphenyl)-1,1-binaphthyl-2,2-diyl hydrogenphosphate (TRIP) catalyzes the asymmetric allylation of aldehydes with organozinc compounds, leading to highly valuable structural motifs, like precursors to lignan natural products. Our previously reported mechanistic proposal relies on two reaction intermediates and requires further investigation to really understand the mode of action and the origins of stereoselectivity. Detailed ab initio calculations, supported by experimental data, render a substantially different mode of action to the allyl boronate congener. Instead of a Brønsted acid-based catalytic activation, the chiral phosphate acts as a counterion for the Lewis acidic zinc ion, which provides the activation of the aldehyde.