Ketyl radical reactivity via atom transfer catalysis

Abstract

Single-electron reduction of a carbonyl to a ketyl enables access to a polarity-reversed platform of reactivity for this cornerstone functional group. However, the synthetic utility of the ketyl radical is hindered by the strong reductants necessary for its generation, which also limit its reactivity to net reductive mechanisms. Herein, we report a strategy for net redox-neutral generation and reaction of ketyl radicals. The in situ conversion of aldehydes to α-acetoxy iodides lowers their reduction potential (Δ 1200 mV), allowing for milder access to the corresponding ketyl radicals and an oxidative termination event. Upon subjecting these iodides to a Mn2(CO)10 pre-catalyst and visible light irradiation, an atom transfer radical addition (ATRA) mechanism affords a broad scope of vinyl iodide products with high Z-selectivity.

Generation and Reactivity of Amidyl Radicals: Manganese‐Mediated Atom‐Transfer Reaction

“…As expected, unactivated tertiary CÀH bonds in cyclic and acyclic systems could be selectively chlorinated (9,10). Likewise, site-specific chlorination of primary C(sp 3 ) À H bonds is successful (11). This method can be broadened to benzylic CÀH chlorination, as supported by the synthesis of 12.…”

“…Prominently, several important precedents in photoinduced manganese-catalyzed/promoted atom-transfer reactions have been reported by the groups of Giese, [5] Parsons, [6] Friestad, [7] Ryu, [8] Alexanian, [9] Fadeyi, [10] and Nagib. [11] However, all these reactions focus on the formation of carbon-centered radicals with alkyl halides as the C-radical precursors (Scheme 1 a). Consequently, the exploitation of atom-transfer reactions facilitated by earth-abundant manganese catalysis to generate other radicals, especially heteroatom-centered radicals, will be of high value to the synthetic chemistry field.…”

Photocatalyst-Independent Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides: Stereocontrol and Mechanism

“…25,26 The utilization of earthabundant metals as visible-light photocatalysts has recently gained great interest in order to develop sustainable photocatalysts. 27 Recent reported light-induced metal catalysts include Cu, [28][29][30][31] Co, [32][33][34][35] Ni, 26,[36][37][38] Mn, [39][40][41] Ce [42][43][44][45] and Fe 46,47 complexes. Such metal complexes usually involve photoinduced single-electron transfer (SET) between substrate and catalyst, and allow for reactions that occur directly from their photoexcited states, without the assistance of exogenous photocatalysts that harvest light to transfer electron or energy.…”

Direct transfer of tri- and di-fluoroethanol units enabled by radical activation of organosilicon reagents

“…The broad applicability and general utility of the approach are highlighted by late-stage introduction of fluoroalkyl groups to complex molecules, such as the derivatives from biologically active naturally occuring epiandrosterone, cholesterol, testosterone, diosgenin, vitamin E, estrone, and (8α)-estradiol, and the synthesis of antitumor agent Z and its difluoromethyl analog Z′. Moreover, our radical reactions show conjunctive group tolerance to that of the traditional nucleophilic fluoroalkylation reactions with α-fluoro carbanions 3,20,21 (Radical reactions often show different reactivity to the anionic reactions, see refs. 20,21 ).…”