Iron-catalyzed 1,3-dipolar cycloaddition of alkynes and aryl nitrones for the synthesis of chiral Δ4-isoxazolines

The synthesis of chiral Δ4-isoxazolines is a crucial area of research due to their biological activity and versatility in synthetic chemistry. Driven by the abundant reserves, low cost and high biocompatibility of iron catalysts, we herein investigated the catalytic potential of iron complexes in asymmetric 1,3-dipolar cycloaddition reactions between N-Bn,α-aryl nitrones and 3-propioloyloxazolidin-2-ones. By utilizing Fe(OTf)2 and (S,S)-DBFOX-Ph, a series of (R)-Δ4-isoxazolines were obtained in high yields (up to 99%) with good to excellent enantioselectivities (up to 98 : 2 er). Additionally, using Fe(OTf)3 and (±)-BINOL as the catalyst, good to excellent yields (up to 99%) and diastereoselectivities (up to >20 : 1 dr) were achieved for the (S,S)-Δ4-isoxazoline derivatives from 3-propioloyloxazolidin-2-ones bearing a chiral Evans auxiliary. Gram-scale synthesis and synthetic utility were also demonstrated.

Sc(OTf)3-catalyzed [3 + 2]-cycloaddition of nitrones with ynones

An efficient approach to access functionalized (2,3-dihydroisoxazol-4-yl) ketones has been developed by reacting nitrones 4 with ynones 7 or terminal ynones 10 in a one-pot fashion. The reaction went through a formal Sc(OTf)3-catalyzed [3 + 2]-cycloaddition process to generate a number of functionalized (2,3-dihydroisoxazol-4-yl) ketones 11aa-11aw, 11ba-11la and 12aa-12ae in moderate to good yields.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Asymmetric "Acetylenic" [3+2] Cycloaddition of Nitrones Catalyzed by Cationic Chiral PdII Lewis Acid

Highly enantioselective [3+2] cycloaddition of ynones and nitrones has been developed. Very bulky ligand, DTBM-SEGPHOS, was used for an effective asymmetric induction over distal reaction centers on the linear ynone dipolarophile and for prevention of Pd^II catalyst deactivation by coordination of the nitrones. The reaction has wide scope of substrates in both ynones and nitrones.