Intermolecular one-pot cyclization of formyl-pyrroles of amino acid esters with norephedrine: stereoselective routes to new tricyclic pyrrole-pyrazine-oxazole fused structures

The treatment of esters of amino acids with dimethoxytetrahydrofuran furnished pyrrole derivatives of amino acid esters. The Wilsmeier-Haack formylation followed by the reaction of the formylated pyrroles with norephedrine afforded a selective formation of the tricyclic pyrrole-pyrazine-oxazole fused structures in one step via the formation of an oxazoline structure and intramolecular lactam formation. Pyrrole-pyrazine-oxazole fused structures were achieved in good yields. The cyclization reaction for the formation of an oxazole ring worked selectively to form only one stereoisomer. The configuration of the newly generated stereogenic center in the oxazole ring is dependent on the stereogenic centers of norephedrine. (c) 2006 Elsevier Ltd. All rights reserved.