Divergent Reactivity of Nitrocyclopropanes with Huisgen Zwitterions and Facile Syntheses of 3‑Alkoxy Pyrazolines and Pyrazoles

A novel annulation reaction of <i>trans</i>-2-substituted-3-nitrocyclopropane-1,1-carboxylates with in situ generated Huisgen zwitterions is reported, providing facile synthesis of 3-alkoxy pyrazolines in good yields and high diastereoselectivities. This reaction unveils the divergent reactivity of the nitrocyclopropanes as a kind of versatile donor–acceptor cyclopropanes. It is also demonstrated that the prepared 3-alkoxy pyrazolines from di-<i>tert</i>-butyl azodicarboxylate can be readily transformed into the corresponding 3-alkoxy 1<i>H</i>-pyrazoles in moderate yields

Divergent Reactivity of Nitrocyclopropanes with Huisgen Zwitterions and Facile Syntheses of 3‑Alkoxy Pyrazolines and Pyrazoles

A novel annulation reaction of <i>trans</i>-2-substituted-3-nitrocyclopropane-1,1-carboxylates with in situ generated Huisgen zwitterions is reported, providing facile synthesis of 3-alkoxy pyrazolines in good yields and high diastereoselectivities. This reaction unveils the divergent reactivity of the nitrocyclopropanes as a kind of versatile donor–acceptor cyclopropanes. It is also demonstrated that the prepared 3-alkoxy pyrazolines from di-<i>tert</i>-butyl azodicarboxylate can be readily transformed into the corresponding 3-alkoxy 1<i>H</i>-pyrazoles in moderate yields

P(NMe₂)₃‑Mediated Reductive (1 + 4) Annulation Reaction of Isatins with Nitroalkenes: An Access to Spirooxindolyl Isoxazoline <i>N</i>‑Oxides and Their Corresponding Isoxazolines

The reductive (1 + 4) annulation reaction of isatins and substituted nitroalkenes mediated by a trivalent phosphorus reagent has been realized for the first time, providing easy access to spirooxindolyl isoxazoline <i>N</i>-oxides in moderate to excellent yields with a flexible substrate scope. This reaction presumably proceeds through a Michael addition–intramolecular substitution sequence via active in situ generated Kukhtin–Ramirez zwitterions from isatins and P­(NMe₂)₃. It is also demonstrated that the spirooxindolyl isoxazoline <i>N</i>-oxides can be readily converted into the corresponding isoxazolines in good yields

Phosphine-Catalyzed (4 + 1) Annulation of <i>o</i>‑Hydroxyphenyl and <i>o</i>‑Aminophenyl Ketones with Allylic Carbonates: Syntheses and Transformations of 3‑Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines

A phosphine-catalyzed (4 + 1) annulation reaction of <i>o</i>-hydroxyphenyl and <i>o</i>-aminophenyl ketones with ester-modified allylic carbonates has been developed, providing a facile and efficient method to synthesize functionalized 2,3-disubstituted dihydrobenzofurans and indolines. Under mild conditions and in the catalysis of PPh₃ (20 mol %), the reactions of <i>o</i>-hydroxyphenyl or <i>o</i>-aminophenyl ketones readily furnish highly functionalized 3-hydroxy-2,3-disubstituted dihydrobenzofurans or 3-hydroxy-2,3-disubstituted indolines in 40–99% yields with generally high diastereoselectivity. To further expand the utility of this annulation reaction to the synthesis of functionalized benzofurans and indoles, the CuSO₄-promoted chemical transformations of the annulation products have also been studied

Annulation Reaction of 3‑Acylmethylidene Oxindoles with Huisgen Zwitterions and Its Applications in the Syntheses of Pyrrolo[4,3,2-<i>de</i>]quinolinones and Marine Alkaloids Ammosamides

A novel annulation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions is unveiled that leads to an unprecedented synthetic method for complex pyrrolo­[4,3,2-<i>de</i>]­quinolinones and marine alkaloids ammosamides A–C. This method features simplicity, high efficiency, and broad substrate scope and is accordingly anticipated to significantly facilitate the preparation and bioassay of the relevant pyrroloquinoline alkaloids and their analogues

Highly Chemoselective Rauhut–Currier Reaction between Maleimides and Enones and Dual Phosphine-Mediated One-Pot Synthesis of Bicyclic and Polycyclic Skeletons

A highly chemoselective phosphine-catalyzed Rauhut–Currier reaction between maleimides and enones has been realized under very mild conditions, affording the corresponding cross-coupling products in moderate to excellent yields. On the basis of this reaction, an efficient dual phosphine-mediated one-pot synthesis of bicyclic and polycyclic compounds containing a cyclopenta­[<i>c</i>]­pyrrole skeleton has been accordingly developed, which features a tandem sequence of intermolecular Rauhut–Currier reaction and intramolecular Wittig reaction

Highly Chemoselective Rauhut–Currier Reaction between Maleimides and Enones and Dual Phosphine-Mediated One-Pot Synthesis of Bicyclic and Polycyclic Skeletons

A highly chemoselective phosphine-catalyzed Rauhut–Currier reaction between maleimides and enones has been realized under very mild conditions, affording the corresponding cross-coupling products in moderate to excellent yields. On the basis of this reaction, an efficient dual phosphine-mediated one-pot synthesis of bicyclic and polycyclic compounds containing a cyclopenta­[<i>c</i>]­pyrrole skeleton has been accordingly developed, which features a tandem sequence of intermolecular Rauhut–Currier reaction and intramolecular Wittig reaction

Goodyera indet.

A new phosphine-triggered tandem [3 + 4] annulation reaction between Morita–Baylis–Hillman carbonates and 1,4-diheteroatom dinucleophiles has been developed, which provides a facile synthetic method for saturated seven-membered 1,4-heterocycles such as 1,4-oxazepanes, 1,4-thiazepanes, and 1,4-diazepanes. Mechanistic investigation implies that this reaction takes place through a phosphine-catalyzed allylic alkylation followed by a general base-catalyzed intramolecular Michael cyclization

Phosphine-Catalyzed (4 + 1) Annulation of <i>o</i>‑Hydroxyphenyl and <i>o</i>‑Aminophenyl Ketones with Allylic Carbonates: Syntheses and Transformations of 3‑Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines

A phosphine-catalyzed (4 + 1) annulation reaction of <i>o</i>-hydroxyphenyl and <i>o</i>-aminophenyl ketones with ester-modified allylic carbonates has been developed, providing a facile and efficient method to synthesize functionalized 2,3-disubstituted dihydrobenzofurans and indolines. Under mild conditions and in the catalysis of PPh₃ (20 mol %), the reactions of <i>o</i>-hydroxyphenyl or <i>o</i>-aminophenyl ketones readily furnish highly functionalized 3-hydroxy-2,3-disubstituted dihydrobenzofurans or 3-hydroxy-2,3-disubstituted indolines in 40–99% yields with generally high diastereoselectivity. To further expand the utility of this annulation reaction to the synthesis of functionalized benzofurans and indoles, the CuSO₄-promoted chemical transformations of the annulation products have also been studied

P(NMe₂)₃‑Mediated Reductive (1 + 4) Annulation Reaction of Isatins with Nitroalkenes: An Access to Spirooxindolyl Isoxazoline <i>N</i>‑Oxides and Their Corresponding Isoxazolines

The reductive (1 + 4) annulation reaction of isatins and substituted nitroalkenes mediated by a trivalent phosphorus reagent has been realized for the first time, providing easy access to spirooxindolyl isoxazoline <i>N</i>-oxides in moderate to excellent yields with a flexible substrate scope. This reaction presumably proceeds through a Michael addition–intramolecular substitution sequence via active in situ generated Kukhtin–Ramirez zwitterions from isatins and P­(NMe₂)₃. It is also demonstrated that the spirooxindolyl isoxazoline <i>N</i>-oxides can be readily converted into the corresponding isoxazolines in good yields