The coupling of enolates through single electron oxidation is one of the most direct routes to generating 1,4-dicarbonyls. Recent work on the intermolecular heterocoupling of equimolar amounts of two different enolates through single electron oxidation has shown that synthetically useful yields beyond those statistically predicted can be obtained. To determine the underlying basis for the selective formation of heterocoupled products, kinetic, 7Li NMR, and synthetic studies were performed. The collection of data obtained from these experiments show that the selective formation of heterocoupled products is a consequence of heteroaggregation of lithium enolates.

A straightforward method for the synthesis of γ-halo-substituted ketones formed via the CANinitiated oxidative addition of halides to 1-substituted cyclobutanols has been developed. This method has short reaction times, and provides access to a range of bromo and iodo γ-substituted ketones in good to excellent yields.

This report describes the scope and mechanism of the solvent-dependent, chemoselective oxidative coupling of 1-aryl-1,3-dicarbonyls with styrene using Ce(IV) reagents. Dihydrofuran derivatives are obtained when reactions are performed in methanol whereas α-tetralones can be selectively synthesized in acetonitrile and methylene chloride. Mechanistic studies are consistent with the rate of solvent-assisted deprotonation of a radical cation intermediate playing an integral role in the selective formation of products.

SummaryThe synthesis of 2-tetralones through the cyclization of δ-aryl-β-dicarbonyl substrates by using CAN is described. Appropriately functionalized aromatic substrates undergo intramolecular cyclizations generating 2-tetralone derivatives in moderate to good yields. DFT computational studies indicate that successful formation of 2-tetralones from δ-aryl-β-dicarbonyl radicals is dependent on the stability of the subsequent cyclohexadienyl radical intermediates. Furthermore, DFT computational studies were used to rationalize the observed site selectivity in the 2-tetralone products.

A convenient approach for the synthesis of tetrasubstituted pyrazoles is described. The method involves the treatment of 1,3-diketones and allyltrimethylsilane with CAN followed by cerium-catalyzed addition of substituted hydrazines to construct pyrazoles in good yields.