Switchable Synthesis of Spirodihydroindolizines and Indolizines from Aurones and Pyridin-2-yl Active Methylene Compounds.

A novel and flexible domino reaction of aurones with pyridin-2-yl active methylene compounds promoted by I2/BF3 has been developed to afford spirodihydroindolizines and indolizines in a controllable manner. When the reaction was performed in 1,2-dichloroethane at 80 °C, a variety of spirodihydroindolizines were obtained, whereas it almost exclusively provided a series of indolizines when the reaction was performed in a mixed solvent of 1,2-dichloroethane and N,N-dimethylformamide at a relatively higher temperature of 100 °C. Being metal-free, excellent product selectivity, high atom economy, good functional group tolerance, and feasibility for large-scale synthesis are the salient features of the developed methodology.

Aerobic CuBr2-Catalyzed Oxidative Coupling Reaction of Amidines with Exocyclic α,ß-Unsaturated Cycloketones for the Synthesis of Spiroimidazolines.

A CuBr2-catalyzed cascade reaction of amidines with exocyclic α,ß-unsaturated cycloketones was developed, affording a large variety of spiroimidazolines in moderate to excellent yields. The reaction process involved the Michael addition and copper(II)-catalyzed aerobic oxidative coupling, in which O2 from air acted as the oxidant and H2O was the sole byproduct.

Kinetic Resolution of Racemic Allylic Alcohols by Catalytic Asymmetric Substitution of the OH Group with Monosubstituted Hydrazines.

A new strategy has been established for the kinetic resolution of racemic allylic alcohols through a palladium/sulfonyl-hydrazide-catalyzed asymmetric OH-substitution under mild conditions. In the presence of 1 mol % [Pd(allyl)Cl]2 , 4 mol % (S)-SegPhos, and 10 mol % 2,5-dichlorobenzenesulfonyl hydrazide, a range of racemic allylic alcohols were smoothly resolved with selectivity factors of more than 400 through an asymmetric allylic alkylation of monosubstituted hydrazines under air at room temperature. Importantly, this kinetic resolution process provided various allylic alcohols and allylic hydrazine derivatives with high enantiopurity.

Palladium/copper-catalyzed oxidative arylation of terminal alkenes with aroyl hydrazides.

An unprecedented oxidative arylation reaction of terminal alkenes with simple aroyl hydrazides has been developed under aerobic conditions for the stereoselective synthesis of 1,2-disubstituted alkenes. A range of aroyl hydrazides underwent palladium/copper-catalyzed oxidative Mizoroki-Heck reaction with terminal alkenes open to air in a 1:1 mixture of dimethyl sulfoxide and acetonitrile to give structurally diverse 1,2-disubstituted alkenes in moderate to excellent yields with excellent regio- and E-selectivity. The reaction tolerated a wide variety of functional groups, such as alkoxy, hydroxy, amino, fluoro, chloro, bromo, cyano, nitro, ester, amide, imide, phosphine oxide, and sulfone groups, and, moreover, molecular oxygen and dimethyl sulfoxide were demonstrated to serve as terminal oxidants. This study provides a useful method for the stereoselective synthesis of 1,2-disubstituted alkenes through direct transformation of the vinylic CH bonds in terminal alkenes.

Highly Regioselective Carbamoylation of Electron-Deficient Nitrogen Heteroarenes with Hydrazinecarboxamides.

The use of hydrazinecarboxamides as a new class of carbamoylating agents has been established through the dehydrazinative Minisci reaction of electron-deficient nitrogen heteroarenes. A wide range of electron-deficient nitrogen heteroarenes, including isoquinoline, quinoline, pyridine, phenanthridine, quinoxaline, and phthalazine, underwent copper/acid-catalyzed oxidative carbamoylation with hydrazinecarboxamide hydrochlorides to afford structurally diverse nitrogen-heteroaryl carboxamides as single regioisomers in moderate to excellent yields. The functional group tolerance was substantially demonstrated in the direct carbamoylation of quinine obviating multistep sequences involving protecting groups and prefunctionalization of the heterocycle.