Dioxazoles, a new mild nitrene transfer reagent in gold catalysis: highly efficient synthesis of functionalized oxazoles

Abstract

A gold-catalyzed regioselective [3+2] cycloaddition of ynamides with 1,4,2-dioxazoles was developed and offers a novel approach to obtain highly functionalized oxazoles under mild reaction conditions. 1,4,2-Dioxazole was found to act as an efficient N-acyl nitrene equivalent to trigger a facile generation of α-imino gold-carbene intermediate through the elimination of a ketone.

α‐Imino Gold Carbene Intermediates from Readily Accessible Sulfilimines: Intermolecular Access to Structural Diversity

“…[15] Chemists can benefit from exploiting such methodologies for rapid synthesiso rl atestage modification of biologically importantc ompounds. Under this principle, as eries of cyclic nitrenoid precursors, including 2H-azirines, [17] isoxazoles, [18] 1,2,4-oxadiazoles, [19] 1,4,2dioxazoles, [20] 4,5-dihydro-1,2,4-oxadiazoles, [21] 2,1-benzisoxazoles, [22] 1,2-benzisoxazoles, [23] pyrido[1,2-b]indazoles, [24a] and triazapentalenes [24b,c] have been developed for the direct introductiono fn itrogen-containing heterocyclic frameworks, whereas the corresponding gold carbenes generally underwent al imited number of transformations (Scheme 1A). By contrast, azides [25] and pyridium aza-ylides [26] potentially provide more opportunities to obtain reactiona nd product diversity (Scheme 1B).…”

Regiodivergent Control in the Gold(I) Catalyzed Synthesis of 7‐Pyrazolylindoles from 1‐Propargyl‐1H‐benzotriazoles and Ynamides through α‐Imino Gold(I) Carbene Complexes

“…[5] In addition to the use of azides, other procedures involving intra-or intermolecular attacks to gold activated alkyne derivatives have been performed. Thus, pyridine-N-aminides, [6] 2H-azirine derivatives, [7] isoxazoles, [8] oxadiazoles, [9] dioxazoles, [10] indazoles [11] or directly from a gold-catalyzed decomposition of diazo compounds [12] have demonstrated to be alternatives. On the other hand, we have recently reported in this field an efficient procedure for the synthesis of 2-imidazolyl-1-pyrazolylbenzenes from propargylbenzotriazoles, alkynes and nitriles (Figure 1), [13] with the participation of isolable triazapentalenes as nucleophiles.…”

Development of Gold‐catalyzed [4+1] and [2+2+1]/[4+2] Annulations between Propiolate Derivatives and Isoxazoles

“…[1] These reactions focus intensively on electron-rich ynamides, [2] and recently on electron-deficient propiolates. [1] These reactions focus intensively on electron-rich ynamides, [2] and recently on electron-deficient propiolates.…”

“…[6] Hashmi and coworkers reported distinct [3+ +2] annulations of ynamides with benzo[c]isoxazoles to ]. W es eek new annulations of isoxazoles with alkynes beyond three-atom building units.T his work reports two distinct annulations between isoxazoles and propiolates,t hus yielding 2,] and 3,8-dicarbonylimidazo [1,2-a]pyridines [Eq. (1) and (2)].…”

“…Gold-catalyzed annulations of alkynes with weak nucleophiles are powerful tools to access highly functionalized carbo-or heterocycles. [1] These reactions focus intensively on electron-rich ynamides, [2] and recently on electron-deficient propiolates. [3] Isoxazoles are important aromatic heterocycles which exist in many bioactive molecules.…”