From Ketones to Esters by a Cu-Catalyzed Highly Selective C(CO)–C(alkyl) Bond Cleavage: Aerobic Oxidation and Oxygenation with Air

Abstract

The Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage has been developed. Varieties of common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration, electron-deficient phenols, as well as various natural alcohols. The usage of inexpensive copper catalyst, broad substrate scope, and neutral and open air conditions make this protocol very practical. (18)O labeling experiments reveal that oxygenation occurs during this transformation. Preliminary mechanism studies indicate that two novel pathways are mainly involved in this process.

A Boron Protecting Group Strategy for 1,2-Azaborines

“…At the outset of this project, we tested the activity of the readily available N -H, B - n -Bu azaborine 1 14 under conditions 17 adapted from Jiao and co-workers (Scheme 3). We were delighted to find that a 11 B NMR spectrum of the reaction revealed the complete consumption of B -butyl azaborine 1 ( 11 B shift ~35 ppm) and appearance of a peak corresponding with the desired B -butoxy material 2 14 ( 11 B shift ~30 ppm) and a minor peak assigned to one or more B(OR) 3 species produced as undesired side products ( 11 B shift ~20 ppm).…”

Nitrogen Dioxide Catalyzed Aerobic Oxidative Cleavage of C(OH)–C Bonds of Secondary Alcohols to Produce Acids

“…Subsequently, dioxetane intermediate f is generated and NO 2 radical is released, which is due to intramolecular cyclization reactions. Dioxetane intermediate f was further thermally cleaved, yielding carbonyl‐containing acid product g and aldehyde h (Supporting Information, Figure S8a) . Aldehyde h would transfer to stable acid by‐product i under alkaline condition…”

Copper catalyzed oxygen assisted C(CNOH)–C(alkyl) bond cleavage: a facile conversion of aryl/aralkyl/vinyl ketones to aromatic acids

“…Based on the recent publications on the oxidative C-C bond cleavage of acetophenones, [5][6][7][8] and inspired by a report by Chiba et al for the cleavage of α-keto imino copper intermediates 12 we aimed for the C-C bond cleavage that is adjacent to oxime. This may lead to the formation of corresponding nitriles.…”