Exo-Selective Intramolecular C–H Alkylation with 1,1-Disubstituted Alkenes by Rare-Earth Catalysts: Construction of Indanes and Tetralins with an All-Carbon Quaternary Center

Abstract

We report herein the exo-selective, regiospecific annulation of a wide range of functionalized aromatic substrates with 1,1-disubstituted alkenes through C(sp 2 )−H and benzylic C(sp 3 )−H activation by half-sandwich rare-earth catalysts. This protocol offers a straightforward and atom-efficient route for the synthesis of a family of indane and tetralin derivatives bearing an all-carbon quaternary stereocenter that were difficult to access previously by other catalysts. The reaction mechanism has been elucidated by deuterium-labeling experiments and DFT calculations.

Regioselective C–H alkylation of anisoles with olefins by cationic imidazolin-2-iminato scandium(iii) alkyl complexes

“… 6 In contrast, rare-earth organic complexes benefit from their unique chemical properties and have been successfully disclosed to be efficient promoters by Hou and others. 3 Taking advantage of the strong oxophilicity of rare-earth metal ions and their high activity towards olefin migration insertion, Hou and co-workers first accomplished intermolecular and intramolecular C–H bond addition of anisoles to various alkenes with cationic half-sandwich yttrium( iii ) or scandium( iii ) alkyl complexes as the catalysts (cat-1 and cat-2; Scheme 1b , left). 3 a , c In 2019, the group of Chen extended alkene substrates to 1,5-dienes and 1,6-dienes under the influence of cationic 2-picoline-tether-half-sandwich scandium( iii ) alkyl catalyst (cat-3).…”

“…1 The development of succinct and efficient approaches for the production of anisoles and their derivatives has therefore attracted significant interest in the past few decades. 2–5 In particular, the C–H alkylation of anisoles with alkenes represents one of the most atom-efficient and environmentally benign synthetic routes. 2–4 Although the well-known Friedel–Crafts type reactions of anisoles with alkenes via carbocation intermediates have been extensively investigated with Lewis and Brønsted acids as the catalysts, the control of regioselectivity has been problematic; a mixture of ortho - and para -regioisomers are always concomitantly generated in the reaction process (Scheme 1a).…”

“…2–5 In particular, the C–H alkylation of anisoles with alkenes represents one of the most atom-efficient and environmentally benign synthetic routes. 2–4 Although the well-known Friedel–Crafts type reactions of anisoles with alkenes via carbocation intermediates have been extensively investigated with Lewis and Brønsted acids as the catalysts, the control of regioselectivity has been problematic; a mixture of ortho - and para -regioisomers are always concomitantly generated in the reaction process (Scheme 1a). 2 The metal–organic complex-mediated C–H alkylation of anisoles with alkenes via C–H activation is an alternative pathway to obtain alkylated anisoles.…”

“…2 The metal–organic complex-mediated C–H alkylation of anisoles with alkenes via C–H activation is an alternative pathway to obtain alkylated anisoles. 3,4 However, owing to the weak interaction between late-transition metals and the ether moiety, the use of transition metal-based catalysts in such transformations is fruitless. 6 In contrast, rare-earth organic complexes benefit from their unique chemical properties and have been successfully disclosed to be efficient promoters by Hou and others.…”

In situ fluorescence visualizing of a temperature-dependent photoreaction process of pyridazine N-oxide

“…The deep understanding and precise control of organic reaction processes are of great significance to both basic research and industrial production. [1][2][3] However, in recent years, laboratory or industry accidents have occurred frequently due to delayed or improper monitoring of reaction processes. 4,5 Therefore, rapid, sensitive, real-time and in situ monitoring of reaction processes is critical for production safety.…”