Abstract
The p-TsOH-catalyzed Diels–Alder reaction of 3-(indol-3-yl)maleimides with chalcone in toluene at 60 °C afforded two diastereoisomers of tetrahydropyrrolo[3,4-c]carbazoles, which can be dehydrogenated by DDQ oxidation in acetonitrile at room temperature to give the aromatized pyrrolo[3,4-c]carbazoles in high yields. On the other hand, the one-pot reaction of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones with chalcones or benzylideneacetone in acetonitrile in the presence of p-TsOH and DDQ resulted in polyfunctionalized carbazoles in satisfactory yields. The reaction mechanism included the DDQ oxidative dehydrogenation of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones to the corresponding 3-vinylindoles, their acid-catalyzed Diels–Alder reaction and sequential aromatization process.
Highlights
Carbazole is one of the most well-known privileged nitrogencontaining heterocycles
The carbazole skeleton is widely occurring in natural alkaloids and pharmacologically active compounds representing a broad spectrum of important bioactivities such as anticancer, antituberculosis, anti-protein kinase C, antipsychotic, and antioxidative activities [1-5]
By using the one-pot domino synthetic strategy of in situ-generated 2-vinyl- or 3-vinylindolines and sequential Diels–Alder reaction with activated dienophiles, we have successfully developed several efficient synthetic protocols for diversely functionalized tetrahydrocarbazoles and the corresponding carbazole derivatives [41-47]
Summary
Carbazole is one of the most well-known privileged nitrogencontaining heterocycles. The carbazole skeleton is widely occurring in natural alkaloids and pharmacologically active compounds representing a broad spectrum of important bioactivities such as anticancer, antituberculosis, anti-protein kinase C, antipsychotic, and antioxidative activities [1-5]. Many efficient synthetic methodologies for functionalized carbazole derivatives have been successfully developed [12-18]. The Diels–Alder reaction of activated 2-vinylindolines or 3-vinylindolines with diverse dienophiles has become the most attractive strategy for the synthesis of carbazole deriv-. By using the one-pot domino synthetic strategy of in situ-generated 2-vinyl- or 3-vinylindolines and sequential Diels–Alder reaction with activated dienophiles, we have successfully developed several efficient synthetic protocols for diversely functionalized tetrahydrocarbazoles and the corresponding carbazole derivatives [41-47]. To further demonstrate the synthetic application of domino Diels–Alder reactions and in continuation of our aim to providing efficient domino reactions for the synthesis of biologically important carbazole derivatives [48-53], we wish to report the DDQ-mediated dehydrogenative Diels–Alder reaction of 3-(indol-3-yl)maleimides and benzoyl-substituted 3-ethylindoles with readily available chalcones for the convenient synthesis of polyfunctionalized carbazole derivatives
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