Recent progress in mild Csp³–H bond dehydrogenative or (mono-) oxidative functionalization

Abstract

Over the past few years, the development of oxidative methodologies towards efficient and selective direct Csp-H bond functionalization processes has attracted tremendous attention from synthetic chemists. However, only a little attention has been given to the key role of the nature of the oxidant. This review aims at providing a brief summary of the recent advances in mild and more benign oxidative Csp-H bond functionalization reactions, which are classified according to the type of oxidation system employed.

Copper‐Catalyzed Allylic C−H Alkynylation by Cross‐Dehydrogenative Coupling

“…Following this breakthrough, various efficient methods have been developed for sp 3 C−H bond functionalization and subsequent coupling with sp, sp 2 and sp 3 C−H bonds under relatively mild reaction conditions with good selectivity . One apparent limitation of the CDC approach is that most derivatizations occur at α‐C−H bonds to heteroatoms such as nitrogen and oxygen due to the prompt formation of iminium and oxonium ions, respectively, under oxidative conditions (Scheme B) …”

“…[16a, 17] One apparent limitation of the CDC approach is that mostd erivatizations occur at a-CÀHb onds to heteroatoms such as nitrogen and oxygen due to the prompt formation of iminium and oxoniumi ons, respectively,u nder oxidative conditions (Scheme 1B). [18] In as eminalr eport, Li and co-workers described the first catalytic allylic alkylationr eaction coupling an allylic sp 3 carbon with am ethylenic sp 3 carbon using ac ombination of CuBr and CoCl 2 as catalysts and as toichiometrica mount of tert-butylh ydroperoxide (TBHP) as the oxidant. [19] However,t he extension of this methodology to terminal alkynes has, so far,r emained elusive.…”

Light‐Driven Single‐Electron Transfer Processes as an Enabling Principle in Sulfur and Selenium Multicatalysis

“…Over the last couple of years,t he number of methods involving chalcogen species as co-catalysts (chalcogen = S, Se) [6] within integrative multicatalytic regimes has steadily increased. [7,8] In common cases,t he sulfur and selenium species function as highly redox active catalysts that readily undergo oxidation state changes (e.g. S 0 /S I and Se I /Se II ) through single-electron transfer (SET) processes with their respective co-catalysts (e.g.e lectro- [9] or photoredox catalysts [8, 10a,11] ).…”

Recent Advances on Copper-Catalyzed C–C Bond Formation via C–H Functionalization

“…25 However, the use of these oxidants generates high amounts of waste and thus limits the applicability of CDC reactions in sustainable applications. 26 Fostered by these concerns, new CDC methodologies have been recently developed that use oxygen (ideally from air) as the terminal oxidant, producing water as the only by-product, even though their widespread use has been hampered by safety concerns.…”