Trans-Concerted Addition to Alkynes: the case of Ynamide Silylzincation.

Authors :: Guégan F
Chemla F
Ferreira F
Gérard H
Perez-Luna A
Halbert S
Source :: Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2024 Aug 01; Vol. 30 (43), pp. e202401751. Date of Electronic Publication: 2024 Jul 11.
Publication Year :: 2024
Abstract: An original concerted antarafacial mechanism for the addition of diorganosilyl-zinc reagents across the C-C triple bond of ynamides is computationally investigated using DFT calculations. This concerted mechanism, leading to a trans-product in only one step, results in the formation of a Si-C and a Zn-C σ-bond on opposite sides of the π-system. We demonstrate that the mechanism going through a η <superscript>2</superscript> -vinyl intermediate and the proposal of a radical chain pathway are energetically unsustainable. The retained concerted antarafacial pathway is tested on experimental selectivities: the regioselectivity, in favor of the silyl β-addition in ynamide, and stereoselectivity, which is cis- with (Me <subscript>2</subscript> PhSi) <subscript>2</subscript> Zn but trans- with [(Me <subscript>3</subscript> Si) <subscript>3</subscript> Si] <subscript>2</subscript> Zn, are well reproduced by DFT calculations. The regio- and stereoselectivity are discussed using the activation strain model and a chemical bonding analysis.<br /> (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)