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The ortho-selective benzylic C(sp3)–H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity. [ABSTRACT FROM AUTHOR]

Half‐sandwich rare‐earth dialkynyl complexes are of much interest in both structure and reactivity but have remained much underexplored to date. Here we report the synthesis and transformation of a new family of half‐sandwich dialkynyl complexes bearing the C5Me4SiMe3 ligand, which exhibited diverse structural features depending on metal ion size, alkyne substituent and with or without THF coordination. The acid‐base reactions between half‐sandwich rare earth dialkyl complexes (C5Me4SiMe3)Ln(CH2SiMe3)2(THF) (Ln=Sc, Y, Lu) and two equivalents of terminal alkynes such as phenylacetylene and trimethylsilylacetylene in THF generally gave the corresponding THF‐coordinated monomeric rare earth dialkynyl complexes, which upon recrystallization from toluene yielded further aggregated alkynyl complexes with partial or full dissociation of the THF ligands. In the case of phenylacetylene, trimeric yttrium and lutetium hexaalkynyl complexes were formed, in which each pair of the metal atoms was bridged by two alkynyl ligands in solid state but the alkynyl ligands underwent rapid site exchange in toluene solution. In the case of trimethylsilylacetylene with yttrium and lutetium, dimeric tetraalkynyl complexes bearing two terminal and two bridging alkynyl ligands were obtained from toluene. In contrast, recrystallization of the scandium trimethylsilylacetylide complex from toluene induced alkynyl coupling and yielded dimeric scandium complex with one butatrienediyl and two alkynyl bridging ligands. Upon dissolution in THF, all the aggregated alkynyl/butatrienediyl complexes were rapidly reconverted to the monomeric dialkynyl complexes as a result of THF coordination to the rare earth metal atoms. [ABSTRACT FROM AUTHOR]

The search for efficient and selective methods for the divergent synthesis of multi‐substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2‐methyl aromatic aldimines with alkenes via benzylic C(sp3)−H activation by half‐sandwich rare‐earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi‐substituted 1‐aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C5Me4SiMe3 or C5Me5 exclusively afforded the trans‐selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis‐selective annulation products. This protocol features 100 % atom‐efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates. [ABSTRACT FROM AUTHOR]

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four‐membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio‐ and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino‐functionalized alkenes by half‐sandwich rare‐earth catalysts. The reaction proceeded through an allene C(sp2)−H activation mechanism initiated by the site‐selective deprotonation of the allene unit by a rare‐earth metal alkyl species followed by alkene insertion into the resulting metal‐allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously. [ABSTRACT FROM AUTHOR]

Here we report for the first time the regio‐ and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β‐C(sp3)−H bond by half‐sandwich scandium catalysts. This protocol offers a straightforward and atom‐efficient route for the synthesis of a new family of multi‐substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5‐aryl‐trans‐substituted 1‐aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1‐insertion of a styrene unit. The annulation of aldimines with aliphatic alkenes selectively gave the 4‐alkyl‐trans‐substituted 1‐aminocyclopentane products in a 1,2‐insertion fashion. A catalytic amount of an appropriate amine such as adamantylamine (AdNH2) or dibenzylamine (Bn2NH) showed significant effects on the catalyst activity and stereoselectivity. [ABSTRACT FROM AUTHOR]

The [3 + 2] or [4 + 2] annulation of α,β-unsaturated aldimines with alkenes via β'- or γ-allylic C(sp 3 )-H activation is, in principle, an atom-efficient route for the synthesis of five- or six-membered-ring cycloalkylamines, which are important structural motifs in numerous natural products, bioactive molecules, and pharmaceuticals. However, such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. We report herein for the first time the regio- and diastereoselective [3 + 2] and [4 + 2] annulations of α,β-unsaturated imines with alkenes via allylic C(sp 3 )-H activation by half-sandwich rare-earth catalysts having different metal ion sizes. The reaction of α-methyl-substituted α,β-unsaturated aldimines with alkenes by a C 5 Me 4 SiMe 3 -ligated scandium catalyst took place in a trans -diastereoselective [3 + 2] annulation fashion via C(sp 3 )-H activation at the α-methyl group (β'-position), exclusively affording alkylidene-functionalized cyclopentylamines with excellent trans -diastereoselectivity. In contrast, the reaction of β-methyl-substituted α,β-unsaturated aldimines with alkenes by a C 5 Me 5 -ligated cerium catalyst proceeded in a cis -diastereoselective [4 + 2] annulation fashion via γ-allylic C(sp 3 )-H activation, selectively yielding multisubstituted 2-cyclohexenylamines with excellent cis -diastereoselectivity. The mechanistic details of these transformations have been elucidated by deuterium-labeling experiments, kinetic isotope effect studies, and the isolation and transformations of key reaction intermediates. This work offers an efficient and selective protocol for the synthesis of a new family of cycloalkylamine derivatives, featuring 100% atom efficiency, high regio- and diastereoselectivity, broad substrate scope, and an unprecedented reaction mechanism.

The search for efficient and selective methods for the divergent synthesis of multi-substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2-methyl aromatic aldimines with alkenes via benzylic C(sp 3 )-H activation by half-sandwich rare-earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi-substituted 1-aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C 5 Me 4 SiMe 3 or C 5 Me 5 exclusively afforded the trans-selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis-selective annulation products. This protocol features 100 % atom-efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates., (© 2024 Wiley-VCH GmbH.)

The exploration into challenging scenarios of the application of elementary reactions offers excellent opportunities for the development of unique transformations under organometallic catalysis. As a ubiquitous reaction of metal alkyl complexes, β-hydride elimination plays a crucial role in a number of important catalytic transformations. However, its functions in these catalytic cycles are limited to either releasing alkene products or generating isomerized intermediates through further migratory insertion. Herein, we report that the precise manipulation of β-hydride elimination enables an auto-tandem copper catalysis for the carboxylation of undirected alkenyl C-H bonds with CO 2 . In this transformation, β-hydride elimination of an alkyl copper intermediate is facilitated, while its reaction with CO 2 is suppressed. The resulting copper hydride in turn reacts with CO 2 to provide access to a multitasking catalyst, which enables the tandem borylation/carboxylation of C-H bonds in two mechanistically distinct catalytic cycles.

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four-membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio- and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino-functionalized alkenes by half-sandwich rare-earth catalysts. The reaction proceeded through an allene C(sp 2 )-H activation mechanism initiated by the site-selective deprotonation of the allene unit by a rare-earth metal alkyl species followed by alkene insertion into the resulting metal-allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously., (© 2022 Wiley-VCH GmbH.)

The creation of self-healing polymers from commodity olefins is of great interest and importance but has remained a challenge to date. We report here for the first time the synthesis of self-healing polymers by catalyst-controlled polymerization of a simple commodity diene, isoprene. We found that polyisoprenes having an appropriate mixture (ca. 70/30) of 3,4- and cis-1,4-microstructures synthesized by using a half-sandwich scandium catalyst could act as excellent self-healing elastomers without any external intervention. The unprecedented self-healability could be ascribed to nanoscale heterogeneities formed by microphase separation of the relatively hard 3,4-segments from a flexible cis-1,4-segment matrix. The hydrogenated polyisoprenes (without C=C bonds) with the analogous microstructures also exhibited excellent mechanical and self-healing properties, further demonstrating that even simple polyolefins can be made self-healable if the microstructures are appropriately regulated., (© 2022 Wiley-VCH GmbH.)

The ortho -selective benzylic C(sp 3 )-H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity.

Here we report for the first time the regio- and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β-C(sp 3 )-H bond by half-sandwich scandium catalysts. This protocol offers a straightforward and atom-efficient route for the synthesis of a new family of multi-substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5-aryl-trans-substituted 1-aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1-insertion of a styrene unit. The annulation of aldimines with aliphatic alkenes selectively gave the 4-alkyl-trans-substituted 1-aminocyclopentane products in a 1,2-insertion fashion. A catalytic amount of an appropriate amine such as adamantylamine (AdNH 2 ) or dibenzylamine (Bn 2 NH) showed significant effects on the catalyst activity and stereoselectivity., (© 2021 Wiley-VCH GmbH.)

The terpolymerization of a non-polar olefin (such as ethylene) and two different polar functional olefins in a controlled fashion is of great interest and importance but has hardly been explored to date. We report for the first time the terpolymerization of ethylene (E) and two different methoxyaryl-substituted propylenes (A R1 P=hexylanisyl propylene; A R2 P=methoxynaphthyl propylene or methoxypyrenyl propylene) by a half-sandwich scandium catalyst. The terpolymerization took place in a sequence-controlled fashion, affording unique multi-block copolymers composed of two different ethylene-alt-methoxyarylpropylene sequences E-alt-A R1 P (soft segments) and E-alt-A R2 P (hard segments) and relatively short ethylene-ethylene (EE) blocks (crystalline segments). The terpolymers exhibited excellent elasticity and unprecedented self-healing as a result of microphase separation of nanodomains of the crystalline EE segments and the hard amorphous E-alt-A R2 P segments from a very flexible E-alt-A R1 P matrix, demonstrating unique synergy of the three different components., (© 2021 Wiley-VCH GmbH.)