A Valuable Upgrade to the Portfolio of Cycloaddition Reactions

Abstract

Cycloadditions maintain an aura of scientific glamour because of their almost magical organization of multiple components and because of the elegant orbital symmetry rules that underpin them. Cyclotrimerizations are a sub-group in this reaction portfolio, with [2+2+2] cycloadditions being the most familiar. The archetype of this group is the combination of three alkynes to produce benzenes [Scheme 1, equ.

Copper-Catalyzed Amination of C(sp3)–H bonds: From Anilides to Indolines

“…On the basis of these results and precedent studies, ,− we proposed plausible reaction pathways in Scheme , although various alternative pathways are possible (see the Supporting Information for details). In the presence of DTBP, CuX is known to be oxidized to Cu­(II) by the reaction with t BuO radical or with DTBP with the generation of t BuO radical .…”

“…In any cases, the corresponding product 2a was not formed, suggesting that a radical intermediate(s) is involved. When CuBr and NMI ( N -methylimidazole) were added to a mixture of DTBP and p -Cl-C 6 H 4 CH 3 in C 6 D 6 (Figure ), a shift of the t BuO signal from 1.23 to 1.08 ppm was observed for 2h by 1 H NMR analysis, implying a possible formation of a Cu (II/III)-O t Bu complex or t BuOH. − …”

Radical asymmetric intramolecular α-cyclopropanation of aldehydes towards bicyclo[3.1.0]hexanes containing vicinal all-carbon quaternary stereocenters

“…Moreover, the sterically hindered ortho -substituted substrate 1s also provided the desired product 2s in 62% yield and 93:7 er. In sharp contrast to the previous works 32 – 35 , the mild reaction conditions make this asymmetric transformation have excellent functional group tolerance, particularly for the ones that are usually incompatible in radical-involved reactions under harsh conditions (halides, carbonyl groups, or NO 2 ). In addition, 3,5-disubstituted and 3,4,5-trisubstituted substrates were also suitable for this reaction, delivering the bicyclo[3.1.0]hexane products 2u and 2x in 89.5:10.5 and 92.5:7.5 er, respectively.…”

“…Recently, impressive progress has been achieved in the development of intermolecular cyclopropanation of olefins using simple methyl group as C1 source 32 – 35 , which has obvious advantages over reactive prefunctionalized precursors with respect to availability of the starting materials, operation safety, environmental benignity, and atom economy. In particular, Antonchick and co-workers reported a seminal work on copper(I)-catalyzed intermolecular [2 + 1] cycloaddition of electron-deficient alkenes with the methyl group in aryl methyl ketones as C1 source for the construction of cyclopropanes with good efficiency through a radical process 33 .…”

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

“…Metal-catalyzed alkyne trimerization via [2+2+2] cycloaddition to form aromatic compounds has been documented in the review literature. − Here, ruthenium-catalyzed alkyne [2+2+2] cycloadditions are catalogued on the basis of catalyst structure. Intermolecular alkyne [2+2+2] cycloadditions, as well as reactions of tethered diynes with alkynes and completely intramolecular reactions of acyclic triynes are all described in this section.…”