Renée Paugam

Diastereoselective cycloaddition of alkylidenecyclopropane nitrones from palladium(0)-catalyzed nucleophilic substitution of asymmetric 1-alkenylcyclopropyl esters by amino acids

Abstract The asymmetric construction of perhydropyrrolo[3,4- b ]pyridine derivatives was performed by chemo- and regioselective formation of enantiopure alkylidenecyclopropane nitrones, followed by diastereoselective intramolecular 1,3-dipolar cycloaddition. The resulting spirocyclopropane isoxazolidines then underwent thermally induced regioselective ring expansion into optically active diazaheterocycles.

High degree of exo selectivity in imino Diels-Alder reactions catalyzed by tert-butyldimethylsilyltriflate

Abstract Diels-Alder reactions of silyloxydiene 1 derived from 1-acetylcyclohexene with imines 2b and 2c occur with high exo selectivity depending upon experimental conditions: exo cycloadducts 3b–c are exclusively formed under kinetic control using tert-butyldimethylsilytriflate as catalyst. In the presence of AlCl3, under thermodynamic control, high endo selectivity is only observed with 2b.

Intramolecular Cycloaddition/Rearrangement of Alkylidenecyclopropane Nitrones from Palladium(0)‐Catalyzed Alkylation of Amino Acid Derivatives

Several alkylidenecyclopropanes have been synthesized in high yields and optical purity by palladium(0)-catalyzed substitution of 1-tosyloxy-1-vinyl cyclopropane using N-tosylamino esters or glycolic ester as nucleophiles. The new alkylidenecyclopropanes were transformed to the corresponding nitrones without loss of optical purity, except in the case of the phenylglycine derivative. The alkylidenecyclopropane nitrones underwent smooth in situ intramolecular cycloaddition with a stereoselectivity that was moderate with most substituted substrates, but complete with phenylglycine and proline derivatives. The spirocyclopropane isoxazolidines were transformed by selective thermal rearrangements in octahydro-2H-pyrrolo[3,4-b]pyridin-7-ones and octahydrofuro[3,4-b]pyridin-7-one, uncommon ring systems resembling biologically active natural and nonnatural products. An example of the extension of the process to an alkylidenecyclopropane nitrile oxide is also reported.

Stereoselective synthesis of cis ring fused endo or exo octahydropyrindin-4 ones by imino-Diels-Alder reaction

The Diels-Alder reaction of trimethylsilylenolether of 1-acetylcyclopentene 1b with benzylideneaniline 2, catalyzed by AlCl3, occurred with high exo or endo selectivity, depending upon kinetic or thermodynamic control. MeOH/Et3N treatment of the intermediate cycloadducts 3 and 4 gave stereospecifically the cis ring fused exo or endo octahydropyrindin-4 onex 5 and 6 while α,β unsaturated ketones 8 or 9 were formed after acidic treatment. Basic isomerization of 6 afforded the corresponding trans ring fused endo ketone 7.

Interpretation of the Diastereoselectivity of the Cyclopropane Formation Involving π-Allyl Palladium Complexes Based on Molecular Mechanics Calculations

Abstract The diastereoselectivity of the base-induced cyclization of 2-amino-4-chlorobutyronitrile derivatives and of the palladium (0) catalyzed tandem alkylation and cyclization of ( E )- and ( Z )-1,4-dichlorobut-2-enes, providing suitable precursors of asymmetric 2,3-methanoamino acids, was interpreted by means of molecular mechanics calculations based on the MM2 force field. The dummy atom concept for the construction of η 3 -allyl palladium complexes and a new parameter set for the calculation have been used. The observed diastereoselectivity which resulted from simple kinetic or thermodynamic control, can be however altered in some cases by the palladium-induced reversibility of the three-membered ring formation.