Switching Electrophile Intermediates to Nucleophiles: Michael and Oxa-Diels-Alder Reactions to Afford Polyoxy-Functionalized Piperidine Derivatives with Tetrasubstituted Carbon

One-Pot Stereoselective Synthesis of the Naphthofurano-Iminosugars via a [3 + 2] Cycloaddition Reaction

This study presents the synthesis of novel naphthofurano-iminosugars (4) using 2,3-O-isopropylidene D-ribose tosylate (1a), anilines (2), and 1,4-benzoquinone (3a) as starting materials through key iminium ion/enamine intermediates via [3 + 2] cyclization reactions at room temperature. The reaction has unique regioselectivity and stereoselectivity with moderate to excellent yields. The adaptability of this method has been demonstrated using various substituted anilines, on which both electron-donating and electron-withdrawing groups were well employed in the reactions. Notably, the treatment of the fused multicyclic iminosugar 4 with TFA efficiently leads to an interesting unexpected pyridinium salt (8), possible via four sequential steps: deprotection of the 2,3-O-isopropylidene group, furan ring opening, dehydration condensation of the OH groups, and elimination of water.

DBU-catalyzed diastereoselective 1,3-dipolar [3+2] cycloaddition of trifluoroethyl amine-derived isatin ketimines with chalcones: synthesis of 5'-CF3-substituted 3,2'-pyrrolidinyl spirooxindoles

A diastereoselective 1,3-dipolar cycloaddition reaction between trifluoroethyl amine-derived isatin ketimines and chalcones was successfully achieved in the presence of DBU. A series of 5'-CF3-substituted 3,2'-pyrrolidinyl spirooxindoles were efficiently synthesized with high yields and excellent diastereoselectivities (up to 89% yield, and >99 : 1 dr). The in vitro anticancer activities of these highly functionalized spiro[pyrrolidin-3,2'-oxindole] derivatives were evaluated.

Palladium-Catalyzed Arylation of Endocyclic 1-Azaallyl Anions: Concise Synthesis of Unprotected Enantioenriched cis-2,3-Diarylpiperidines

Unprotected cis-2,3-diarylpiperidines are synthesized through an unprecedented palladium-catalyzed cross-coupling reaction between aryl halides and elusive endocyclic 1-azaallyl anions. These intermediates are generated in situ by the deprotonation of 2-aryl-1-piperideines, precursors that are readily prepared in two operations from simple piperidines. An asymmetric version of this reaction with (2R, 3R)-iPr-BI-DIME as the ligand provides products in moderate to good yields and enantioselectivities. This study significantly expands the synthetic utility of endocyclic 1-azaallyl anions.

Recent advances in the synthetic applications of Morita-Baylis-Hillman and Rauhut-Currier adducts of nitroalkenes

The Morita-Baylis-Hillman (MBH) and Rauhut-Currier (RC) adducts of nitroalkenes are important synthetic intermediates in organic synthesis. This review discusses the applications of different MBH and RC adducts of nitroalkenes such as MBH alcohols, acetates, bromides and hydrazinonitroalkenes as well as ketoalkylnitroalkenes in the synthesis of complex molecules including carbocycles and heterocycles. It also covers the mechanistic aspects, including the key intermediates and the reaction pathways. Early reports on MBH and RC reactions of nitroalkenes and applications of the products were covered in previous reviews. The present review covers the reports that appeared in the timeline of 2015-2023.

Organocatalytic (5+1) benzannulation of Morita–Baylis–Hillman carbonates: synthesis of multisubstituted 4-benzylidene pyrazolones

DABCO-catalyzed (5+1) cycloaddition of MBH carbonate undergoes an α-double deprotonation pathway to de novo assemble the benzene ring.

Intramolecular Formal [4 + 2] Cycloadditions: Synthesis of Spiro Isoindolinone Derivatives and Related Molecules

Acid-catalyzed intramolecular reactions of isoindolinone-derived hydroxylactam derivatives bearing enones or enals that afford spiro isoindolinone derivatives and related molecules have been developed. From the hydroxylactam moieties, N-acylenamides were generated in situ and reacted with the enone and the enal moieties via formal [4 + 2] cycloaddition reactions to construct cyclohexanone- and dihydropyran-fused ring systems and the spiro ring systems.