Chiral Spirophosphoric-Acid-Catalyzed Divergent Vinylogous Mannich and -Friedel-Crafts Reactions of 2-Methoxyfuran.

The first enantioselective vinylogous Mannich reaction is developed using 2-methoxyfuran under chiral spirophosphoric acid catalysis. The strategy involves 4-isoxazoline derivatives as cyclic ketimine surrogates and provides γ-butenolide scaffolds (up to 97% ee and >20:1 dr). The mechanistic investigations suggest that an generated water molecule plays a crucial role in delivering γ-butenolide, while the use of molecular sieves delivers -Friedel-Crafts products.

Doyle-Kirmse Reaction on Alkynyl Hydrazone Carboxylates: Synthesis of 1,4-Allenyne and 1,5-Enyne Thioaryl Carboxylates.

The first Doyle-Kirmse reaction on alkynyl diazoacetates using allyl/propargyl sulfides is reported. The development provides diversified 1,5-enyne and 1,4-allenyne thioaryl carboxylates in good yields under ligand-/additive-free AuCl and Rh(OAc) catalysis, respectively (48 examples, up to 96% yield). The study demonstrated the dual role of allyl sulfide as a ligand and substrate.

Synthesis of Tetrasubstituted 1,4-Dicarbonyl ()-2,3-Dihaloalkenes via Electrophilic Halogenation of Alkynyl Hydrazones.

A highly practical and stereoselective route to 1,4-dicarbonyl 2,3-dihaloalkenes is presented. The strategy involves bench-stable unprotected alkynyl hydrazones and commercially available -halosuccinimides that provide γ-oxo-α,β-()-dihaloenoates in excellent yields with complete -selectivity. The protocol also furnishes vicinal dihaloalkenes with two different halogen atoms.

Decomposition of Alkynyl Hydrazones: Synthesis of Allenoates, Dihaloallenoates, and Angularly Fused Tricyclic Azepines.

An unprecedented decomposition of unprotected alkynyl hydrazones is attempted that has provided allenoates, tetrasubstituted α,γ-dihaloallenoates, and functionalized tricyclic azepines. A reaction of alkynyl hydrazones with -halosuccinimides captures the electrophile in 2-fold that delivers fully substituted dibromo- and diiodoallenoates in good yields. In addition, a DABCO-promoted Wolff-Kishner reduction of hydrazones, followed by isomerization, provides versatile allenoates under mild conditions.

Synthesis of Alkynyl Hydrazones from Unprotected Hydrazine and Their Reactivity as Diazo Precursors.

Alkynyl hydrazones are synthesized conveniently from 2-oxo-3-butynoates and hydrazine by suppressing the susceptible formation of pyrazoles. The resultant hydrazones are transformed into alkynyl diazoacetates under metal-free and mild oxidative conditions in excellent yields. Further, the alkynyl cyclopropane and propargyl silane carboxylates are synthesized in good yields by developing an unprecedented copper-catalyzed alkynyl carbene transfer reaction.