Stoichiometric Photochemical Carbene Transfer by Bamford–Stevens Reaction

Abstract

The photolysis of diazoalkanes is a timely strategy to conduct carbene‐transfer reactions under mild and metal‐free reaction conditions, and has developed as an important alternative to conventional metal‐catalyzed carbene‐transfer reactions. One of the major limitations lies within the rapidly occurring side reaction of the carbene intermediate with remaining diazoalkane molecules that result in the use of an excess of the reaction partner and thus impacts on the reaction efficiency. Herein, we describe a protocol that takes advantage of the in situ generation of donor–acceptor diazoalkanes by Bamford–Stevens reaction. Following this strategy, the concentration of the diazoalkane reaction partner can be minimized to reduce unwanted side reactions and to now conduct photochemical carbene transfer reactions under stoichiometric reaction conditions. We have explored this approach in the C−H and N−H functionalization and cyclopropanation reaction of N‐heterocycles and could demonstrate the applicability of this method in 51 examples.

External Photocatalyst-Free Visible Light-Promoted 1,3-Addition of Perfluoroalkyl Iodides to Vinyldiazoacetates

“…Despite these significant advances, radical perfluoroalkylation based on the interactions between reactive intermediates and perfluoroalkyl halides remains scarce. Recently, Jurberg and Davies, 49 Koenigs et al, [50][51][52][53][54] Zhou et al, 55 and others [56][57][58] have reported the use of low-energy blue light to liberate free carbenes from donor-acceptor diazo compounds. We wonder whether it is possible to generate R f radicals by forming a transient intermediate between perfluoroalkyl iodides and free carbene (either singlet or triplet), thus initiating the 1,3-ATRA addition of R f I to vinyldiazoacetates.…”

Blue LED Induced Manganese (I) Catalysed Direct C2−H Activation of Pyrroles with Aryl Diazoesters

“…[13] To circumvent this problem Jana and co-workers reported in situ generation of donor-acceptor diazoalkanes from the corresponding hydrazone and base, via Bamford Stevens reaction and demonstrated the reaction in a single example of N-methyl pyrrole and phenyldiazo acetate. [14] Here in, we used Mn(CO) 5 Br as a catalyst that formed metal carbene to stabilize the carbene the moment it formed photolytically from the corresponding diazoesters (Scheme 1e). The metal carbenes then react with the pyrrole to provide the desired C2À H activated product in good to excellent quantity.…”

“…However the major drawback of this strategy is undesired interactions of carbene intermediates with unreacted diazoesters that further complicates the reaction mixture and hence deters the reaction efficiency [13] . To circumvent this problem Jana and co‐workers reported in situ generation of donor‐acceptor diazoalkanes from the corresponding hydrazone and base, via Bamford Stevens reaction and demonstrated the reaction in a single example of N‐methyl pyrrole and phenyldiazo acetate [14] . Here in, we used Mn(CO) 5 Br as a catalyst that formed metal carbene to stabilize the carbene the moment it formed photolytically from the corresponding diazoesters (Scheme 1e).…”

Unlocking novel reaction pathways of diazoalkanes with visible light

“…Other solvents, such as ethers, alcohols, acetonitrile, cycloalkanes or aromatic solvents are however incompatible due to side reactions with solvent molecules and lead, for example, to the formation of norcaradienes in the case of benzene solvent. 39,41 Following the initial reports, different groups disclosed their efforts in the development of further applications of photochemical singlet carbene transfer reactions using donor/acceptor diazoalkanes as carbene precursors to now enable a broad variety of transformations, ranging from cycloadditions 39–44 and rearrangements 45–47 towards X–H 48–51 and C–H functionalization 44,52,53 reactions under catalyst-free and mild reaction conditions. The main advantages of the photochemical approach lie within operational simplicity of the synthesis methods that typically do not require the exclusion of moisture or air.…”

“…This reactivity thus significantly differs from the classic carbene or metal–carbene chemistry, which provides access either to the cyclopropane 43 or the C3-alkylation product (Scheme 11b). 11,52,77…”