Catalytic asymmetric propargyl- and allylboration of hydrazonoesters: a metal-free approach to sterically encumbered chiral α-amino acid derivatives

Abstract

Metal-free asymmetric catalysis for the synthesis of sterically encumbered amino-acids was developed using allyl- and allenylboronic acid reagents.

Organocatalytic insertion into C–B bonds by in situ generated carbene: mechanism, role of the catalyst, and origin of stereoselectivity

“…As shown in Scheme 1b, the chiral organocatalyst can be introduced and increases the activity of the organoboron reagent to generate actual active species, which subsequently plays a critical role in controlling and inducing the stereoselectivity in these kinds of reactions. 9…”

Organocatalytic Synthesis of α-Trifluoromethyl Allylboronic Acids by Enantioselective 1,2-Borotropic Migration

“…Isoquinoline derivative , 6h reacted with purified 1d to afford 7m with 93% ee in 54% yield. Allylboration of 6i , with 1a gave α-amino acid derivative 7n with 98% ee in 72% yield.…”

An expeditious route to sterically encumbered nonproteinogenic α-amino acid precursors using allylboronic acids

“…7 k Recently, allylboronic acids have emerged as a powerful alternative to their allylboronate counterpart due to the more Lewis acidic boron atom, which results in a more organized transition state, leading to greater stereocontrol and, consequently, the diastereo- and enantioselective allylation of different acyclic and cyclic imines and hydrazonoesters has been developed. 9 In 2018, Szabó and co-workers developed a metal-free, enantioselective allylboration of hydrazonoesters using allylboronic acids to get sterically hindered α-amino acid derivatives ( Scheme 1c ). 9 f To the best of our knowledge, there has been no report on the diastereoselective allylation of N-tert -butane sulfinyliminoesters using allylboronic acids.…”