Photocatalytic Regioselective Difunctionalization of Alkenes with Diazo Compounds and tert-Butyl Nitrite: Access to γ-Oximino Esters

Abstract

A visible-light photocatalytic regioselective difunctionalization of alkenes with diazo compounds and tert-butyl nitrite has been developed. The protocol provides an efficient approach to γ-oximino esters under mild conditions. Significantly, this transformation not only shows the good compatibility of nucleophilic diazo compounds and electrophilic tert-butyl nitrite but also displays diazo compounds generating alkyl radicals that preferred addition to alkenes over nitroso radicals.

Photocatalytic Three-Component Synthesis of 3-Heteroarylbicyclo[1.1.1]pentane-1-acetates

“…Based on the combined results of our mechanistic studies and previously published literature reports, an overall reaction mechanism for this transformation type could be proposed as detailed in Scheme f. Initially, upon irradiation with blue LED light, the Ir III complex is converted into the photoexcited species Ir III* ,which is then reductively quenched by DABCO to generate the corresponding species Ir II and DABCO •+ . The newly formed Ir II then reduces the alkyl diazoacetate 1 through a PCET process (proton absorption from trace amounts of H 2 O present in DCM and subsequent N 2 release) to form the corresponding carbon-centered radical I and regenerating the ground state of Ir III to facilitate a new round of this photocatalytic cycle .…”

“…Initially, upon irradiation with blue LED light, the Ir III complex is converted into the photoexcited species Ir III *,which is then reductively quenched by DABCO to generate the corresponding species Ir II and DABCO •+ . 22 The newly formed Ir II then reduces the alkyl diazoacetate 1 through a PCET process (proton absorption from trace amounts of H 2 O present in DCM and subsequent N 2 release) to form the corresponding carbon-centered radical I and regenerating the ground state of Ir III to facilitate a new round of this photocatalytic cycle. 23 In conclusion, we have established a novel synthetic route for 3-heteroarylbicyclo[1.1.1]pentane-1-acetates through a three-component reaction of [1.1.1]propellane, heterocycles, and diazoacetates.…”

C−H Functionalization of Heterocycles with Triplet Carbenes by means of an Unexpected 1,2‐Alkyl Radical Migration**

“…With the goal of understanding the fundamentals of indole CÀ H functionalization and the development of synthetic methods for tryptophol synthesis, we commenced our investigations by studying the reaction of ethyl diazoacetate with indole under photochemical conditions via free carbene intermediates. To overcome limitations of weak absorbance of ethyl diazoacetate (EDA) in the visible light region, we employed photosensitizers as a handle to facilitate its photolysis, [16,[19][20][21][22][23][24] and to promote the formation of carbene intermediates via an energy transfer process. [21,22] In initial studies, we therefore examined the role of the reaction medium and observed a surprising solvent dependency of indole CÀ H functionalization.…”

“…To overcome limitations of weak absorbance of ethyl diazoacetate (EDA) in the visible light region, we employed photosensitizers as a handle to facilitate its photolysis, [16,[19][20][21][22][23][24] and to promote the formation of carbene intermediates via an energy transfer process. [21,22] In initial studies, we therefore examined the role of the reaction medium and observed a surprising solvent dependency of indole CÀ H functionalization. In accordance to previous work by Gryko and co-workers, [16] a good chemoselectivity for C2 functionalization was observed in protic solvents.…”

Heterogeneous Photocatalytic C–H Functionalization of Indoles with Diazo Compounds Enabled by Carbon Nitride

“…In contrast, diazo compounds are less exploited to generate carbon-centered radicals for C–C or C–heteroatom bond formation due to lack of controlled manipulation that converts diazo compounds to carbon radicals rather than carbene intermediates. Recently, a photocatalytic strategy was employed to transform diazo compounds to carbon radical intermediates to construct C–C bonds (Scheme a) . For example, in 2016, Gryko and co-workers found that vitamin B 12 derivatives can catalyze the C–H functionalization of olefins with diazo esters under visible light irradiation .…”