Synthesis of Densely Substituted Sulfonylfurans and Dihydrofurans via Cascade Reactions of α-Functionalized Nitroalkenes with ß-Ketosulfones.

The reaction of ß-ketosulfones with different α-functionalized nitroalkenes affords diversely substituted sulfonylfurans and dihydrofurans. Furthermore, ß-ketosulfones react with α-bromonitroalkenes and α-hydrazinonitroalkenes via a cascade Michael addition-cyclization protocol to afford nitrodihydrofurans and hydrazinodihydrofurans, respectively, bearing a key sulfonyl group, in excellent yields with a broad substrate scope. Application of these products has been demonstrated by the synthesis of pyrroles and pyrazoles in good yields. The reaction of ß-ketosulfones with nitroallylic acetates yields tetrasubstituted sulfonyl furans through a cascade SN2'-intramolecular Michael reaction, followed by aromatization. The gram-scale synthesis of a representative example of sulfonylfurans was carried out to demonstrate the synthetic efficiency of the methodology.

Synthesis of Functionalized Thieno[2,3-b]indoles via One-Pot Reaction of Indoline-2-thiones with Morita-Baylis-Hillman and Rauhut-Currier Adducts of Nitroalkenes.

A straightforward protocol for the synthesis of functionalized thieno[2,3-b]indoles by base-mediated [3 + 2]-annulation of indoline-2-thione with Morita-Baylis-Hillman and Rauhut-Currier adducts of nitroalkenes is described. Complete regioselectivity, broad substrate scope, and mild reaction conditions make this strategy very valuable. Moreover, the thieno[2,3-b]indoles comprising functional groups such as hydrazine and ketoalkyl moieties are amenable for further synthetic elaboration.

Synthesis of Aminophenanthrenes and Benzoquinolines via Hauser-Kraus Annulation of Sulfonyl Phthalide with Rauhut-Currier Adducts of Nitroalkenes.

The Hauser-Kraus reaction of sulfonyl phthalide with nitroalkene derivatives provides access to aminophenanthrenes, including phenanthrene-substituted amino acids and benzoquinolines. The intermediate quinones bearing a key ketoalkyl moiety undergoes facile intramolecular enamine cyclization. Interestingly, enamines derived from primary and secondary amines undergo cyclization via C-centered nucleophilic attack to provide aminophenanthrenes, whereas those derived from ammonia undergo cyclization via N-centered nucleophilic attack leading to benzoquinolines. A one-pot protocol for the direct transformation of phthalides and nitroalkene derivatives to aminophenanthrenes and benzoquinolines has also been developed.

Synthesis of hydrazinoheterocycles from Morita-Baylis-Hillman adducts of nitroalkenes with azodicarboxylates.

Conjugated nitroalkenes and nitrodienes undergo smooth α-hydrazination with azodicarboxylates through an imidazole catalyzed carbon-heteroatom bond formation under Morita-Baylis-Hillman conditions. The resulting hydrazinonitroalkenes take part in 1,3-dipolar cycloaddition with azide under mild conditions to give hydrazinotriazoles. A [3 + 2] annulation with phenols and naphthols involving Michael addition and cyclization as the key steps lead to arenodihydrofurans bearing a key hydrazinodicarboxylate moiety. Both regioisomers of naphthodihydrofurans could be synthesized by our methodology by employing the appropriate naphthol.