A Convergent Synthesis of Enantiopure Open-Chain, Cyclic, and Fluorinated α-Amino Acids.

A radical based synthesis of a broad variety of protected enantiopure α-amino acids, including fluorinated derivatives, is described. The radical addition furnishes naturally latent mercapto-α-amino acids ideally equipped for native chemical ligation.

5-Exo-cyclizations of pentenyliminyl radicals: inversion of the gem-dimethyl effect.

This paper describes how the rates of 5-exo-ring closures of unsaturated iminyl radicals to pyrrolomethyl radicals respond to substituents in the pentenyl chain and at the C=N bond. Benzyl- and acyl oxime esters, as well as dioxime oxalates, were identified as suitable iminyl radical sources for electron paramagnetic resonance (EPR) spectroscopy. Pentenyliminyl radicals with aryl substituents at their C=N bonds, and one with an alkyl substituent at its C=N bond, were studied in solution by steady-state continuous wave EPR spectroscopy.

Microwave-promoted syntheses of quinazolines and dihydroquinazolines from 2-aminoarylalkanone O-phenyl oximes.

A wide range of biologically active compounds contain the quinazoline ring system. A new free-radical-based method of making functionalized quinazolines is described, which relies on microwave-promoted reactions of O-phenyl oximes with aldehydes. A small set of 2-aminoaryl alkanone O-phenyl oximes was prepared and shown to produce dihydroquinazolines when mixed with an aldehyde in toluene and subjected to microwave heating.

From dioxime oxalates to dihydropyrroles and phenanthridines via iminyl radicals.

Dioxime oxalates are useful precursors for the clean generation of iminyl radicals by sensitised UV photolysis and can be adapted for serviceable preparations of 3,4-dihydro-2H-pyrroles and phenanthridines.

Thermal rearrangement of indolyl oxime esters to pyridoindoles.

Acyl oximes derived from a variety of indolylalkanones underwent a ring closure sequence during FVP to afford 9H-pyrido[2,3-b]indoles. Unlike UV light promoted reactions of oxime esters, the mechanism is almost certainly not mediated by iminyl radicals but probably involves tautomerism, elimination of acetic acid, and a final electrocyclic ring closure.

2-(Aminoaryl)alkanone O-phenyl oximes: versatile reagents for syntheses of quinazolines.

Microwave irradiations of 2-(aminoaryl)alkanone O-phenyl oximes and carbonyl compounds generate iminyl radicals in company with imines; iminyl on imine ring closure yields dihydroquinazolines or quinazolines when ZnCl2 is included in the mixture.

Microwave-assisted syntheses of N-heterocycles using alkenone-, alkynone- and aryl-carbonyl O-phenyl oximes: formal synthesis of neocryptolepine.

This research aimed to provide a new and "clean" synthetic method that would enable both known and novel N-heterocycles to be prepared efficiently. O-Phenyl oximes were found to be excellent precursors for iminyl radicals with a variety of acceptor side chains. Dihyropyrroles were made in good yields from O-phenyl oximes containing pent-4-ene acceptors.

Microwave-assisted preparations of dihydropyrroles from alkenone O-phenyl oximes.

Microwave irradiation of alkenone O-phenyl oximes produces iminyl radicals that ring close to yield dihydropyrrole derivatives; pyrroles and pyridines can be obtained from related precursors.