Enantioselective Syntheses of 4H-3,1-Benzoxazines via Catalytic Asymmetric Chlorocyclization of o-Vinylanilides

Electrochemical Thiocyanation/Cyclization Cascade to Access Thiocyanato-Containing Benzoxazines

Due to the importance of SCN-containing heteroarenes, developing novel and green synthetic protocols for the synthesis of SCN-containing compounds has drawn much attention over the last decades. We reported here an electrochemical oxidative cyclization of ortho-vinyl aniline to access various SCN-containing benzoxazines. Mild conditions, an extra catalyst-free and oxidant-free system, and good tolerance for air highlight the application potential of this method.

Iridium-Catalyzed Intramolecular Asymmetric Allylation of Vinyl Benzoxazinones for the Synthesis of Chiral 4H-3,1-Benzoxazines via Kinetic Resolution

Chiral benzoxazinones and 4H-3,1-benzoxazines as important motifs are widely found in abundant pharmaceuticals and biological molecules. We herein successfully developed the first kinetic resolution (KR) process of racemic benzoxazinones through Ir-catalyzed asymmetric intramolecular allylation, furnishing a wide range of chiral benzoxazinones and 4H-3,1-benzoxazines with excellent results via outstanding KR performances (with the s factor up to 170). This protocol exhibited broad substrate scope generality and good functional group tolerance, and the chiral 4H-3,1-benzoxazine products could be readily transformed to other useful optically active heterocycles.

Chiral Lewis Base Catalyzed Enantioselective Selenocyclization of 1,1-Disubstituted Alkenes: Asymmetric Synthesis of Selenium-Containing 4H-3,1-Benzoxazines

An enantioselective selenocyclization of 1,1-disubstituted alkenes was achieved for the first time, which is enabled by a novel combination of a chiral BINAM-derived sulfide and an achiral Lewis acid. Various selenium-containing 4H-3,1-benzoxazines, which are widely present in a range of medicinally relevant molecules, were readily obtained in moderate to good yields and good to excellent enantioselectivities. A series of tetrasubstituted carbon stereocenters were facilely constructed.

Synthesis of Spiro[benzo[d][1,3]oxazine-4,4'-isoquinoline]s via [4+1+1] Annulation of N-Aryl Amidines with Diazo Homophthalimides and O2

Synthesis of spiro[benzo[d][1,3]oxazine-4,4'-isoquinoline]s through a unique [4+1+1] annulation of N-aryl amidines with diazo homophthalimides and O₂ is presented. This unprecedented spirocyclization reaction features readily obtainable substrates, structurally and pharmaceutically attractive products, a cost-free and clean oxygen source, sustainable reaction medium, tolerance of a broad spectrum of functional groups, and an interesting reaction mechanism based on sequential C(sp²)-H/C(sp³)-H bond cleavage and oxygen insertion.

Catalytic enantioselective oxysulfenylation of o-vinylanilides

Tf₂NH-assisted BINAM-derived thiophosphoramide catalysis has been accomplished for the enantioselective oxysulfenylation of o-vinylanilides with N-(aryl/alkylthio)imides. The developed reaction offers access to diverse substituted aryl/alkylthio tethered 3,1-benzoxazines in excellent yields and enantiomeric ratios. Furthermore, synthetic applications of benzoxazines and aryl/alkylthio moieties and a transition state model for the observed enantioselectivity are also discussed.

Synthesis of Tetra-Substituted Trifluoromethyl-3,1-Benzoxazines by Transition-Metal-Catalyzed Decarboxylative Cyclization of N-Benzoyl Benzoxazinones

Efficient synthesis of N,O-heterocyclic tetra-substituted trifluoromethyl-3,1-benzoxazines via a transition-metal-catalyzed decarboxylative intramolecular cyclization was achieved. The decarboxylation of N-benzoyl trifluoromethyl-benzoxazinones generated the amide oxygen nucleophile, allowing a selective internal C1 -attack on Pd- or Cu-coordinated zwitterions, affording medicinally attractive tetra-substituted vinyl- or ethynyl-trifluoromethyl-3,1-benzoxazines. This protocol can be applied to the synthesis of perfluoroalkyl- and non-fluorinated 3,1-benzoxazines.