Visible Light-Promoted Transformation of Diazo Compounds via the Formation of Free Carbene as Key Intermediate

Abstract

Carbene is one of the most important synthetic intermediates in organic synthesis. In the past few decades, transition-metal catalyzed carbene transfer reactions have made remarkable development. Recently, visible light-promoted transformation of diazo compounds through the formation of free carbene as key intermediate begun to rise. The reaction only need visible light as the sole energy source which meets the concept of green chemistry. Since the pioneering works developed by the groups of Diaves and Zhou, photo-promoted transformation of diazo compounds has attracted more and more attentions. On the basis of previous work, the latest progress in this field is further improved, which mainly focuses on the recent new transformation reactions of diazo compounds under visible light irradiation and the contributions reported from Chinese research group. The future development direction, as well as challenges in this field is prospected.

Visible-light-driven multicomponent reactions to access S-alkyl phosphorothioates using elemental sulfur as the sulfur source

“…On the basis of the above results and referring to previous reports, 18 g – j ,19 a plausible pathway for the present multicomponent reactions was proposed as presented in Scheme 3. Firstly, the photolysis of α-diazoesters afforded the carbene intermediate 8 with the release of N 2 under visible-light irradiation.…”

“…Only a few visible-light-initiated multicomponent reactions of α-diazo compounds have been explored owing to the difficulty in the control of the reactivity of the carbene intermediates. 19 With our interest in the photochemical reactions, 20 herein, we wish to report a facile and efficient visible-light-induced multicomponent reactions of α-diazoesters leading to S -alkyl phosphorothioates by using of elemental sulfur as the cheap and odorless sulfur source (Scheme 1e). This photocatalytic protocol provides a mild and green approach to construct a series of S -alkyl phosphorothioates with moderate to good yields in the absence of any photocatalysts or transition metals.…”

Metal-free visible-light-induced multi-component reactions of α-diazoesters leading to S-alkyl dithiocarbamates

“…On the basis of the above experiments and referring to previous reports, 23,25 a possible pathway for the present transformation was proposed as presented in Scheme 4. Firstly, an excited state 1 * was generated from α-diazoester 1 in the presence of light irradiation, which led to the formation of carbene intermediate 6 with the release of nitrogen.…”

“…21,22 In comparison with metal-mediated carbene transfer reactions, photochemical transformations of α-diazo compounds using visible light as the sole energy source could be conducted under milder and greener conditions without the exclusion of moisture or air. 23 In continuation of our interest in photochemical reactions, 24 herein, we wish to report a metal-free and visible-light-mediated protocol for the synthesis of S -alkyl dithiocarbamates from α-diazoesters, amines and CS 2 at room temperature under air, in which nitrogen was generated as the sole side-product (Scheme 1c). Interestingly, when tetrahydrofuran (THF) was used as the solvent, a series of structurally diverse S -alkyl dithiocarbamates could be rapidly and efficiently obtained through a four-component coupling reaction of α-diazoesters, THF, CS 2 , and amines.…”

Elemental sulfur as the “S” source: visible-light-mediated four-component reactions leading to thiocyanates

“…On the basis of the above experiments and referring to previous reports, 22,23 a possible reaction mechanism was proposed as shown in Scheme 4. Firstly, an excited state 1a* was formed under visible-light irradiation.…”