Visible Light Induced Metal-Free Carbene N-Carbazolation

Abstract

Metal-free N–H functionalization reactions represent an important strategy for sustainable C–N coupling reactions. In this report, we describe the visible light photolysis of aryl diazoacetates in the presence of some N-heterocycles that enables mild, metal-free N–H functionalization reactions of carbazole and azepine heterocycles (15 examples, up to 83% yield).

Blue Light‐Promoted N−H Insertion of Carbazoles, Pyrazoles and 1,2,3‐Triazoles into Aryldiazoacetates

“…Of note, during the preparation of our manuscript, Empel, Patureau and Koenigs reported a similar NÀ H insertion strategy employing carbazoles. [22]…”

Stoichiometric Photochemical Carbene Transfer by Bamford–Stevens Reaction

“…The reaction with the latter provides a direct access to biologically important molecules and enables the direct synthesis of an analogue of clopidogrel in good isolated yield. In comparison to our previously reported method for N−H functionalization reactions of carbazole heterocycles, the present method now allows the use of secondary amines and stoichiometric reaction conditions and thus improves on the reaction efficiency (Scheme ).…”

“…In recent years, the visible‐light photolysis of diazoalkanes attracted the interest of organic synthetic chemists to conduct metal‐free carbene‐transfer reactions, and first reports already accentuate its high potential in photochemical, metal‐free cycloaddition, rearrangement, olefination, X−H, and C−H functionalization reactions . Despite these advances, applications are mainly limited to the use of a large excess of one reaction partner due to rapidly occurring side reactions of the carbene intermediate with remaining unreacted diazoalkane molecules, for example, in diazine ( 3 ) formation (Scheme ).…”

“…[1,2] The limitations of this methodology lie within the high reactivityo ft he carbene intermediate and thus unselective downstream reaction, which led to the developmento fm etal-catalyzed carbene-transfer reactions.T he advances in thisr esearch have guidedt he development of highly efficient catalysts, based on preciousm etals, such as Rh, Ir,P d, or Au, and today there several protocols that allow highly efficient and site-selective CÀHf unctionalization reactions. [2,3] In recent years, the visible-light photolysis of diazoalkanes attracted the interest of organic syntheticc hemists to conduct metal-free carbene-transfer reactions, [4][5][6][7][8][9] and first reportsa lready accentuate its high potential in photochemical, metalfree cycloaddition, [6] rearrangement, [6b, 7] olefination, [8] XÀH, [6a, e, 9] and CÀHf unctionalization reactions. [6a] Despite thesea dvances, applicationsa re mainly limited to the use of al arge excesso f one reactionp artner due to rapidly occurring side reactions of the carbene intermediate with remaining unreacted diazoalkane molecules, for example, in diazine (3)f ormation (Scheme 1).Stoichiometric photochemical carbene-transfer reactions are highly attractive and this approach should allow highly atomeconomic transformations under mild reactionc onditions.…”

Photochemical O−H Functionalization Reactions of Cyclic Diazoamides

“…[6] Since then, several groups reported on their studies to promote visible light mediated carbene transfer reactions in highly efficient cycloaddition, XÀ H insertion or olefination reactions. [7,8] In all cases, the irradiation with lowenergy visible light enables an operationally simple and straightforward access to conduct carbene or proton transfer reactions of aryldiazoacetates without the need to exclude air or moisture and simple applicability. [6][7][8][9] More recently, our group was able to expand the photochemical reactivity of diazoalkanes towards photoinduced proton transfer reactions, which now open up a new reactivity pattern of diazoalkanes under photochemical conditions (Scheme 1b).…”