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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]

Transition metal catalyzed C−H functionalization of organic compounds has proved to be a useful atom‐efficient strategy in organic synthesis. In contrast, main‐group‐element‐based catalytic processes for C−H functionalization have remained underexplored to date. Reported herein is the catalytic C(sp)−H silylation of a wide range of terminal alkynes with hydrosilanes by using a combination of B(C6F5)3 and an organic base such as triethylenediamine (DABCO). This protocol constitutes the first example of boron‐catalyzed C(sp)−H functionalization, offering a convenient route for the synthesis of a variety of alkynylsilanes. Experimental and computational studies have revealed that DABCO plays two crucial roles (Lewis base and Brønsted base) in this catalytic transformation. Double duty: The combination of B(C6F5)3 and an organic base, such as triethylenediamine (DABCO), serve as an excellent catalytic system for the C(sp)−H silylation of terminal alkynes with hydrosilanes. DABCO plays two crucial roles (Lewis base and Brønsted base) as revealed by experimental and DFT studies. [ABSTRACT FROM AUTHOR]

An enantioselective C−H addition to a C=C bond represents the most atom-efficient route for the construction of chiral carbon-carbon skeletons, a central research topic in organic synthesis. We herein report the enantioselective yttrium-catalyzed C(sp3)−H bond addition of 2-methyl azaarenes, such as 2-methyl pyridines, to various substituted cyclopropenes and norbornenes. This process efficiently afforded a new family of chiral pyridylmethyl-functionalized cyclopropane and norbornane derivatives in high yields and high enantioselectivities (up to 97 % ee). [ABSTRACT FROM AUTHOR]