Copper-catalyzed cyclopropanation reaction of but-2-ene

Abstract

The mechanism of the copper(I)-catalyzed cyclopropanation reaction for methyl diazoacetate with both (Z)- and (E)-but-2-ene stereoisomers has been studied using the 6-311++G(d,p) basis set by means of M06-2X and O3LYP functionals. According to both methods, the rate-limiting step is the formation of a copper-carbene intermediate, formed by association between methyl diazoacetate and bis(acetonitrile)-copper(I) ion with the concomitant extrusion of dinitrogen. Cis/trans diastereoselectivity for the cyclopropanation reaction of a 1,2-disubstituted alkene ((Z)-but-2-ene) has been theoretically studied for the first time through the proper location of transition states on the potential-energy surface with the O3LYP method, since no transition structures could be found with the M06-2X functional due to the extreme flatness of the potential-energy surface. The calculated stereoselectivities involving two acetonitrile ligands or one dichloromethane molecule show qualitative agreement with experimental data. This study allows attributing the origin of the selectivity to steric interactions between the ligands of the catalyst system and the olefin substituents. The comparison between the corresponding activation barriers for the direct insertion step shows a higher reactivity for the Z stereoisomer of but-2-ene, consistently with the larger reactant destabilization through steric interactions.

Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

“…In order to understand the difference in modification yields by the two catalysts, it is important to consider the mechanistical pathways of the Cu(I)‐catalyzed cyclopropanation reactions. [ 30–31 ] After an initial formation of a precatalyst due to the affinity of the active Cu(I) catalyst for the unsaturated substrate [ 15,29–30,32–34 ] (see Scheme 2, III ), the cyclopropanation proceeds further via complexation of a metal and a carbene ( VI ), formed by expelling N 2 from the diazo compound ( V → VI ), which is considered as the rate determining step. [ 15 ] The ring closing step itself is known to proceed either via a one‐step concerted pathway ( VII ) as a direct‐carbene insertion, or via a two‐step process, proceeding by a metallocyclobutane intermediate ( VIII ), [ 29,32,35 ] depending on the diazo compound, the ligand (L n ) and the transition metal (M).…”

“…In order to understand the difference in modification yields by the two catalysts, it is important to consider the mechanistical pathways of the Cu(I)-catalyzed cyclopropanation reactions. [30][31] After an initial formation of a precatalyst due to the affinity of the active Cu(I) catalyst for the unsaturated substrate [15,[29][30][32][33][34] (see Scheme 2, III), the cyclopropanation proceeds further via complexation of a metal and a carbene (VI), formed by expelling N 2 from the diazo compound (V ! VI), which is considered as the rate determining step.…”

“…S C H E M E 2 Mechanism of the metal-catalyzed cyclopropanation of olefins with diazo compounds. [16,[29][30]32] F I G U R E 3 NMR spectra for EDA in the presence of (a) Catalyst 1 and (b) Catalyst 2. The spectrum (c) is of EDA without a catalyst.…”