Diastereoselective synthesis of fused [1,3]oxazines from ethyl pyruvate, activated acetylenes and N-heterocycles

Rh(III)-Catalyzed Chemoselective [4 + 2] Annulations for the Synthesis of [1,3]Oxazinoindolones: A Combined Experimental and Computational Study

The interaction of N-alkoxy-1H-indole-1-carboxamides with transition metals leads to indole-fused heterocyclic scaffolds through directing group leaving/migration, [3 + 2], N-C2 [4 + 1], and [4 + 2] annulations. However, the corresponding O-C2 [4 + 2] annulation reactions have never been reported. Herein, we report the chemoselective annulation of N-alkoxy-1H-indole-1-carboxamides catalyzed by Rh(III), affording [1,3]oxazinoindolones through a hitherto unknown reaction pathway. This unprecedented C2 oxygen cyclization, rather than the known C2 nitrogen cyclization to form oxazinoindolones via five key steps, has been explained using density functional theory.

Synthesis of Fused [1,3]Oxazines from Ethyl Trifluoroacetate, Activated Acetylenes and N-Heterocycles

The intermediates from the reaction between phenanthridine or isoquinoline with dialkyl acetylenedicarboxylates have been trapped with ethyl trifluoroacetate to produce highly functionalised fused [1,3]oxazines in good yield.

Three-Component Reaction between Pyridine and Activated Acetylenes in the Presence of N’-Arylidenebenzohydrazide as NH-Acids

The one-pot, three-component reaction between pyridine and activated acetylenes in the presence of N’-arylidenebenzohydrazide as NH-acids affords dialkyl 2-[2-( N-benzoyl- N’-arylidenehydrazino)pyridin-1(2 H)-yl]but-2-endioate derivatives which has advantages such as simple work-up, and affording yield.

Three-Component Reaction between N-Methylimidazole and Activated Acetylenes in the Presence of Kojic Acid or 8-Hydroxyquinoline as CH-Acids

We describe a one-pot, three-component reaction between N-methylimidazole and activated acetylenes in the presence of kojic acid or 8-hydroxyquinoline as CH-acids. This affords 2,3-dihydroimidazoles and has advantages such as simple work-up and affording good yields.

Synthesis of benzimidazole[2.1-b][1,3]oxazine spirooxindoles via three-component reaction of N-benzylbenzimidazole, acetylenedicarboxylates, and N-alkylisatins

The three-component reaction of N-benzylbenzimidazole, dialkyl acetylenedicarboxylate, and N-alkylisatins in tetrahydrofuran at room temperature afforded the novel functionalized benzimidazole[2.1-b][1,3]oxazine spirooxindoles in good yields. (1)H NMR spectra indicated that two diastereoisomers with a ratio of 1:3-1:6 exist in the obtained spirooxindole derivatives.