Bryan J. Cowen

Pyridylalanine (Pal)-Peptide Catalyzed Enantioselective Allenoate Additions to N-Acyl Imines

An amine-catalyzed reaction has been discovered that couples alpha-allenic esters with N-acyl imines in good to excellent yields (up to 88%). Extension of this methodology from the study of achiral pyridine-based catalysis to chiral peptide-based scaffolds is presented. The approach culminated in the identification of a tetrameric peptide sequence containing an embedded pyridylalanine (Pal) residue as an efficient asymmetric catalyst for enantioselective coupling reactions. The unique allenic products are obtained with enantiomer ratios of up to approximately 95:5 (up to >98:2 following recrystallization).

Recent Advances in Metal-Free Quinoline Synthesis

The quinoline ring system is one of the most ubiquitous heterocycles in the fields of medicinal and industrial chemistry, forming the scaffold for compounds of great significance. These include anti-inflammatory and antitumor agents, the antimalarial drugs quinine and chloroquine, and organic light-emitting diodes. Quinolines were first synthesized in 1879, and since then a multitude of synthetic routes have been developed. Many of these methods, such as the Skraup, Doebner–Von Miller, and Friedlander quinoline syntheses, are well-known but suffer from inefficiency, harsh reaction conditions, and toxic reagents. This review focuses on recent transition metal-free processes toward these important heterocycles, including both novel routes and modifications to established methods. For example, variations on the Skraup method include microwave irradiation, ionic liquid media, and novel annulation partners, all of which have shown increased reaction efficiency and improved yield of the heteroring-unsubstituted quinoline products. Similarly, modifications to other synthetic routes have been implemented, with the quinoline products displaying a wide variety of substitution patterns.

Mechanism of SmI2 Reduction of 5-Bromo-6-oxo-6-phenylhexyl Methanesulfonate Studied by Spin Trapping with 2-Methyl-2-nitrosopropane

The radical formed by reduction of 5-bromo-6-oxo-6-phenylhexyl methanesulfonate, an α-bromoketone, with SmI2 was spin trapped with 2-methyl-2-nitrosopropane. Electron paramagnetic resonance spectra of the spin adduct and the adduct formed in the analogous reaction with selectively deuterated substrate identify the radical intermediate in this SmI2 reduction as a carbon-centered radical. This result supports the proposal that the formation of reactive Sm-enolates arises from reduction of the carbon-bromine bond rather than a ketyl radical anion.