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.
Highlights
Computational efforts have become a frequent tool in the elucidation of mechanistic scenarios and understanding the course of chemical reactions.[1−3] They allow the evaluation of different events by the comparison of their energetic profiles and deliver useful information to understand and improve the chemistry behind the process of interest.[1−4] Especially in combination with asymmetric synthesis, density functional theory (DFT) calculations have facilitated the finding of asymmetric induction and have delivered or confirmed the accepted mechanistic concept of activation and stereopreference
Allylation reactions have a pronounced foundation and are an indispensable methodology when it comes to the creation of chiral molecules.[5−10] One of these examples is the asymmetric preparation of dibenzylbutyrolactones, which proceeds via the asymmetric allylation of an aldehyde precursor with an organozinc reagent.[11,12]
We have shown that the TRIP-catalyzed asymmetric allylation via zinc reagents proceeds via the zinc salt of the chiral phosphoric acid
Summary
Computational efforts have become a frequent tool in the elucidation of mechanistic scenarios and understanding the course of chemical reactions.[1−3] They allow the evaluation of different events by the comparison of their energetic profiles and deliver useful information to understand and improve the chemistry behind the process of interest.[1−4] Especially in combination with asymmetric synthesis, density functional theory (DFT) calculations have facilitated the finding of asymmetric induction and have delivered or confirmed the accepted mechanistic concept of activation and stereopreference. Important to note is the fact that the reaction has a boron congener, using allyl boronate reagents and the same catalyst.[14] Some efforts have been undertaken to explain the stereoselectivity in case of these reagents, and yielded a mechanistic mode of action, as depicted in Figure 1.15−17 The decrease of the activation barrier is explained by a hydrogen bond to one pinacol oxygen, activating the reagent, whereas the required rigidity for the alignment is reasoned by a formyl-H interaction with the P O oxygen Lewis base. Additional investigations are required to understand the differences of these allylation reactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
