Mechanistic Studies on the Base-Promoted Ring Opening of Glycal-Derived gem-Dibromocyclopropanes

In the presence of a nucleophilic base, ring-fused gem-dibromocyclopropanes derived from d-glycals undergo ring opening to give 2-deoxy-2-(E-bromomethylene)glycosides. Such cleavage of an exocyclic cyclopropane bond contrasts with the more usual silver-promoted ring-expansion reactions in which endocyclic bond cleavage occurs. Experimental and theoretical studies are reported which provide insights into the reaction mechanism and the origin of its kinetic selectivity for E-configured bromoalkene products. Density functional theory computations (M06-2X) predict that the reaction commences with alkoxide-induced HBr elimination from the dibromocyclopropane to form a bromocyclopropene. Ring opening then gives a configurationally stable zwitterionic (oxocarbenium cation/vinyl carbanion) intermediate, which undergoes nucleophilic addition and protonation to give the bromoalkene. There are two competing sources of the proton in the final step: One is the alcohol (co)solvent, and the other is the molecule of alcohol produced during the initial deprotonation step. The roles of the formed alcohol molecule and the bulk (co)solvent are demonstrated by isotope-labeling studies performed with deuterated solvents. The acid-promoted isomerization of the E-bromoalkene product into the corresponding Z-bromoalkene is also described. The mechanistic knowledge gained in this investigation sheds light on the unusual chemistry of this system and facilitates its future application in new settings.

One-pot regioselective synthesis of 2,4-disubstituted quinolines via copper(ii)-catalyzed cascade annulation

A copper(ii)-catalyzed cascade annulation for the one-pot synthesis of 2,4-disubstituted quinolines has been disclosed.

The one-pot synthesis of quinolines via Co(iii)-catalyzed C–H activation/carbonylation/cyclization of anilines

A new and versatile Co(iii)-catalyzed C–H activation/carbonylation/cyclization cascade reaction has been disclosed.

Efficient Preparation of TMSCCl2 Br and Its Use in Dichlorocyclopropanation of Electron-Deficient Alkenes

The reaction of excess TMSCl and LiCCl2 Br at low temperature is a technically simple high yield route to TMSCCl2 Br. The latter is a stable source of the dichlorobromomethide carbanion, which undergoes 1,4-addition with cyclic nitroalkenes and (E)-fumarates leading to dichlorocyclopropanes after bromide expulsion. For nitrostyrenes the reaction arrests at the 1,4-addition product. Low temperature NMR spectroscopy studies and DFT calculations suggest the formation of an "ate" species [(nitronate)SiFMe3 ](-) which, upon boil-off of TMSF at 10-20 °C, yields the cyclopropane. DFT calculations also support the experimental differences between fluoride and acetate as promotors.

Bioactive Phytochemicals: Bioactivity, Sources, Preparations, and/or ModificationsviaSilver Tetrafluoroborate Mediation

This review provides an overview of the biological activities, natural occurrences, and the silver tetrafluoroborate- (AgBF4-) mediated synthesis of proanthocyanidins, glycosides, N-heterocyclic alkaloid analogues (of pyrrole, morphine, quinoline, isoquinoline, and indole), furan analogues, and halocompounds. AgBF4has been reviewed as an effective reaction promoter, used extensively in the synthesis of relevant biologically active compoundsviacarbon-carbon and carbon-heteroatom bonds formation. The literatures from 1979 to April 2014 were reviewed.

Copper-catalyzed oxidative cyclization of enynes for the synthesis of 4-carbonyl-quinolines with O2

A novel copper-catalyzed oxidative cyclization of enynes and in situ formed enynes leading to 4-carbonyl-quinolines by using dioxygen as an oxygen source has been developed.