Herein we describe a new method, enabling the synthesis of highly functionalized 1,4-diketones that are readily differentiated as monosilylenol ethers under Brønsted acid catalysis. This synthetically useful chemistry exploited an intermediacy of unsymmetrical silyloxyallyl cations, which were directly captured by silyl enolates to create the targeted α,α carbon-carbon linkages in a regioselective manner. Our reaction conditions proved to be mild, rendering the silylenol ether functionalities intact.

This report describes Brønsted acid catalyzed de novo synthesis of silyldienol ethers bearing tetrasubstituted double bonds via an intermediacy of 2-silyloxypentadienyl cations. The reactivity of these novel cationic intermediates could be modulated and harnessed toward direct nucleophilic additions regioselectively at the γ-position to produce highly functionalized silyldienol ethers with tunable control of the resulting double bond geometry.

A series of dinuclear copper(I) oxalate complexes was synthesized by the direct acid-base reaction of Cu2O with oxalic acid in ethanol with a ligand, or in neat ligand. The complexes incorporated a variety of ligands L (L = triphenylphosphine, 1,2bis(diphenylphosphino)ethane, triphenylphosphite, diisopropyl sulfide, cyclooctadiene and cyclohexylisocyanide) and had the general formula LnCu(µ2-C2O4)CuLn (n = 1 or 2). The Cu I /Cu II mixed-valence trinuclear compound (iPr2S)2Cu I (C2O4)Cu II (C2O4)Cu I (iPr2S)2 was formed concomitantly with the target dinuclear Cu2C2O4(iPr2S)4 complex, shedding light on the mechanism of disproportionation of this family of complexes. With norbornadiene (nbd) as a ligand, however, a coordination polymer Cu2C2O4(nbd) was formed. Also, the same reaction with L = 2,9-dimethyl-1,10-phenanthroline or pyridine resulted in the known tetrahedral complex ions [CuLm] + (m = 2 or 4). Lastly, the ligand di-2-(1-di-(2-picolyl)amino)propyl 3 disulfide produced not the expected Cu(I) oxalate complex, but a Cu(II) picolylamine oxalate coordination polymer. All products were structurally characterized by single-crystal X-ray diffraction if soluble, and by powder X-ray diffraction methods if not.

We report a new strategy toward the synthesis of highly functionalized carbazoles via 2-(silyloxy)pentadienyl cation intermediates, which were generated upon ionization of vinyl-substituted α-hydroxy silyl enol ethers under Brønsted acid catalysis. These electrophilic species were found to readily undergo cascade reactions with substituted indoles to generate carbazole molecular scaffolds in good yields via a sequence of regioselective nucleophilic addition, followed by intramolecular dehydrative cyclization.