Guangke He

Controlled Synthesis of 1,3,5-Oxadiazin-2-ones and Oxazolones through Regioselective Iodocyclization of Ynamides.

Two efficient processes based on the iodocyclization of ynamides have been developed: (i) N-alkynyl tert-butyloxycarbamates were found to undergo a rare 6-exo-dig ring closure reaction affording 1,3,5-oxadiazin-2-ones by using acetonitrile as solvent; (ii) In the absence of acetonitrile, N-alkynyl tert-butyloxycarbamates could undergo 5-endo-dig cyclization providing oxazolones.

Palladium-Catalyzed Intramolecular Cyclization of Ynamides: Synthesis of 4-Halo-oxazolones

A mild and efficient methodology involving Pd(PPh3)4-catalyzed intramolecular cyclization of N-alkynyl alkyloxycarbamates with CuCl2 or CuBr2 for the synthesis of 4-halo-oxazolones was developed. This reaction exhibiting good functional tolerance provided a new, efficient, and rapid synthetic process to 4-halo-oxazolones. The resulting 4-halo-oxazolones can serve as great potential precursors for the 3,4,5-trisubstituted oxazolones via a Pd-catalyzed cross-coupling reaction.

Cu(I)- or Ag(I)-Catalyzed Regio- and Stereocontrolled trans-Hydrofluorination of Ynamides

With Et3N·3HF as the fluorinating reagent, a copper(I)- or silver(I)-catalyzed β/α-site-regiocontrolled trans-hydrofluorination of alkynamides has been achieved, affording the corresponding fluoro enamides in moderate to nearly quantitative yields with high regio- and stereoselectivity, respectively. The reaction proceeds under mild reaction conditions and exhibits good functional group tolerance. Further, the deuterium-labeling experiment confirmed the existence of the alkenylcopper intermediate.

Generation of Oxazolidine-2,4-diones Bearing Sulfur-Substituted Quaternary Carbon Atoms by Oxothiolation/Cyclization of Ynamides

A novel method for metal-free oxothiolation of ynamides to construct oxazolidine-2,4-diones bearing sulfur-substituted quaternary carbon atoms has been developed. It represents a rare C-O bond cleavage of ynamides, as well as a facile and tandem approach for the formation of C-O, C-S, and C-Cl bonds. This redox-neutral protocol can be applied to the synthesis of multisubstituted oxazolidine-2,4-diones with good chemoselectivity and good yields of isolated products under mild conditions.

A combined experimental and natural bonding orbital charges study on the one-pot regioselective synthesis of 4-chloropyrazoles

The mechanism of a DMF-catalysed electrophilic/nucleophilic chlorination of pyrazole is illustrated with the aid of calculations of the natural bonding orbital charges. Its high regioselectivity and good functionality tolerance of nine pyrazole substrates have been experimentally demonstrated.

1,4-Di-bromo-2,5-di-p-toluoyl-benzene.

In the title compound, C22H16Br2O2, which has approximate non-crystallographic inversion symmetry, the dihedral angles between the central ring and the pendant rings are 89.1 (4) and 82.4 (3)°; the dihedral angle between the pendant rings is 12.1 (4)°. In the crystal, the packing is influenced by van der Waals forces and no aromatic π–π stacking is observed.