Action del l'hydroxyuree sur les composes carbonyles α-ethyleniques. Nouvelle voie de synthese d'isoxazolines-2.

Organocatalysed synthesis of isoxazolines initiated by a chemoselective oxa-Michael reaction of N-BocNHOH

“…1). 11 Despite some seminal experimental observations concerning the oxa-Michael outcome of hydroxyurea NH 2 CONHOH with enals by Petrus and co-workers, 12 the asymmetric developments remain to be achieved. Towards this goal, we are pleased to describe the preliminary results towards an original asymmetric organocatalytic synthesis of 3-isoxazoline carboxylate derivatives.…”

A Versatile Entry to 3-Unsubstituted 2-Isoxazolines

“…3,4 A single example of a reaction between hydroxyurea and crotonaldehyde to give 5-methyl-2-isoxazoline has been reported. 5 Recently, Pennicott el al. also disclosed a method for obtaining these compounds from O-propargylic hydroxylamines.…”

“…We anticipated that these problems could be circumvented by developing a catalyst that would cyclize the conjugate addition product directly to a more stable 2-isoxazoline. The work of Jaquier et al 5 and the recent communication by the Dawson group 8 suggested that this could be well achieved using a suitable amine salt that would be able to catalyze both the conjugate addition and the cyclization step.…”

Action des hydroxyurées sur les maléate et fumarate de méthyle. Obtention des carbométhoxy-5 oxa-6 dihydrouraciles; transposition en carbométhoxyméthylène-5 hydantoïnes

“…Les travaux precedents realises dans notre laboratoire ont permis de mettre en evidence le caractbre "hydroxylamine N-protegee" des hydroxyurees: une attaque par l'atome d'oxygbne est observee dans les reactions d'addition sur les nitriles a-ethyleniques (I), les esters a-kthyleniques (2), les cetones a-ethyleniques (3,4) ainsi que dans les reactions de substitution sur les a-bromoesters (5) Ces resultats permettent de prevoir ii priori une addition-1,4 des hydroxyurees sur les maleate et fumarate de mkthyle.…”