Cleavage of C(aryl)−CH3 Bonds in the Absence of Directing Groups under Transition Metal Free Conditions

• Published in: Angewandte Chemie International Edition Vol. 58; no. 16; pp. 5392 - 5395
• Main Authors: Dai, Peng‐Fei, Ning, Xiao‐Shan, Wang, Hua, Cui, Xian‐Chao, Liu, Jie, Qu, Jian‐Ping, Kang, Yan‐Biao
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 08.04.2019; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Aromatic compounds; borylation; Carbon; Carbonyls; Chemistry; Chemistry, Multidisciplinary; Chemists; Cleavage; cross-coupling; Cyano groups; Decarboxylation; Metals; Organic chemistry; Oxidation; Physical Sciences; Pyridines; radicals; reaction mechanisms; Science & Technology; Transition metals; ACTIVATION; ACID; radicals; CARBON-CARBON BOND; borylation; C-C BOND; cross-coupling; oxidation; reaction mechanisms; ARYL; TERT-BUTYL NITRITE; ACCESS; methyl arene; unactivated C-C bond cleavage; methyl as traceless leaving group; metal-free; unstrained undirected
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201901783

Organic chemists now can construct carbon–carbon σ‐bonds selectively and sequentially, whereas methods for the selective cleavage of carbon–carbon σ‐bonds, especially for unreactive hydrocarbons, remain limited. Activation by ring strain, directing groups, or in the presence of a carbonyl or a cyano group is usually required. In this work, by using a sequential strategy site‐selective cleavage and borylation of C(aryl)−CH3 bonds has been developed under directing group free and transition metal free conditions. Methyl groups of various arenes are selectively cleaved and replaced by boryl groups. Mechanistic analysis suggests that it proceeds by a sequential intermolecular oxidation and coupling of a transient aryl radical, generated by radical decarboxylation, involving a pyridine‐stabilized persistent boryl radical. Without a trace: Using methyl as a traceless leaving group, cleavage of unactivated and unstrained C(aryl)−CH3 bonds is accomplished by a metal‐free process. It proceeds by a sequential intermolecular oxidation and coupling of a transient aryl radical generated by radical decarboxylation.