title: A DFT study of the mechanisms and regio- and stereochemistry of the lewis acid-catalyzed reactions of 5-alkoxyoxazoles with aldehydes: aryl substitution at the 2-position of 5-alkoxyoxazole is critical to the formation of 4-alkoxycarbonyl-2-oxazoline.
abstract: Density functional theory at the B3LYP/6-31G level has been used to study the mechanisms and regio- and stereochemistry of the Lewis acid-catalyzed reactions of aldehydes with 5-alkoxyoxazoles. Similar to the uncatalyzed reaction between aldehyde and 5-methoxyoxazole, which has an activation energy of 30.5 kcal/mol and intrinsically favors production of 2-alkoxycarbonyl-3-oxazoline, the Lewis acid-catalyzed reaction also prefers to generate 2-alkoxycarbonyl-3-oxazoline in a more efficient way with an activation energy of about 3 kcal/mol (with respect to separated acetaldehyde-AlCl3 complex and 5-methoxyoxazole) in the gas phase. Only when an aryl group is introduced to the 2 position of 5-alkoxyoxazoles can the Lewis acid-catalyzed reactions furnish 4-alkoxycarbonyl-2-oxazolines. The reasons for this switch of regiochemistry and the factors affecting the stereochemistry are discussed.
authors.affiliation: Department of Chemistry, The Hong Kong University of Science & Technology, Clearwater Bay, Kowloon, China. zhixiang@chem.ucla.edu
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Yu
authors.forename: Yun-Dong
authors.initials: YD
authors.lastname: Wu