Hetero-Diels-Alder reactions of alpha-aryl-beta-monohalo-alpha-nitrosoethylenes: diastereoselective synthesis of 6-substituted 3-aryl-4-halo-5,6-dihydro-4H-1,2-oxazines

Synthesis of Isoxazolines and Oxazines by Electrochemical Intermolecular [2 + 1 + n] Annulation: Diazo Compounds Act as Radical Acceptors

Reported herein is an unprecedented synthesis of isoxazolines and oxazines through electrochemical intermolecular annulation of alkenes with tert-butyl nitrite, in which diazo compounds serve as radical acceptors. Notably, [2 + 1 + 2] and [2 + 1 + 3] annulations occur when styrenes and allylbenzenes are used as substrates, respectively. The latter reaction undergoes group migration to form more stable radical, manifesting radical route instead of conventional 1,3-dipolar cycloaddition occurs. Moreover, scale-up experiments suggest the potential application value of these transformations in industry.

A newly designed heterodiene and its application to construct six-membered heterocycles containing an N-O bond

A new type of zwitterionic nitrosoalkene generated in situ from dehydrohalogenation of α-halo-N-alkylhydroxamic acids was designed. [4+2] cycloadditions of this heterodiene to olefins provide a facile route to construct six-membered heterocycles containing an N-O bond and a new protocol for 1,2-syn carbohydroxylate alkenes with a hydroxyl and acetamide group. DFT calculations support a concerted cycloaddition pathway and the solvent HFIP can stabilize the transition state through H-bonding interaction.

Pd-Catalyzed carboannulation of γ,δ-alkenyl oximes: efficient access to 5-membered cyclic nitrones and dihydroazines

The Pd⁰-catalyzed carboannulation of γ,δ-alkenyl oximes with organohalides offers catalyst-controlled access to 5-membered cyclic nitrones or 6-membered cyclic oxime ethers.

On water: silver-catalyzed domino approach for the synthesis of benzoxazine/oxazine-fused isoquinolines and naphthyridines from o-alkynyl aldehydes

An operationally simple domino approach for the silver-catalyzed synthesis of oxazine/benzoxazine-fused isoquinolines 5a-q and naphthyridines 6a-v by the reaction of o-alkynyl aldehydes 3a-aa with amines having embedded nucleophiles 4a-d under mild reaction condition in water is described. The reaction shows selective C-N bond formation on the more electrophilic alkynyl carbon resulting in the formation of 6-endo-dig cyclized product. The competitive experiments show the viability of an intramolecular nucleophilic attack over an intermolecular attack of the external nucleophile. This methodology accommodates wide functional group variation, which proves to be useful for structural and biological assessment.

Catalytic diastereo- and enantioselective annulations between transient nitrosoalkenes and indoles

Caught in transition: an efficient catalytic system is the key to the successful development of the first highly diastereo- and enantioselective annulation reaction between indoles and transient nitrosoalkenes. This robust reaction affords structurally unique architectures with up to three new chiral centers. The products can be readily elaborated into other indoline-based chiral heterocyclic motifs, including those of pyrrolidinoindoline alkaloids.

Development of the 1,2-Oxaza-Cope Rearrangement

A method for a concise assembly of oxazine rings based on a Lewis acid-promoted hetero-Cope rearrangement is described. The hetero-Cope rearrangement features the first examples of the [3,3]-sigmatropic transpositions involving the nitroso group. A variety of functionalized substrates have been subjected to the reaction. The described method has a strong potential for the synthesis of marine natural products containing oxazine rings.