Asymmetric Hetero-Diels-Alder Reaction of α-Alkoxy Aldehydes with Activated Dienes. The Scope of Lewis Acid Chelation-Controlled Cycloadditions

Article abstract of DOI:10.1021/jo00304a018

The cycloaddition reactions of various α-alkoxy aldehydes with 1,3-dimethoxy-1-<(trimethylsilyl)oxy>-1,3-butadiene (Brassard's diene, 2) were performed under the Lewis acid catalysis of Eu(hfc)3, magnesium dibromide, or diethylaluminum chloride.Moderate to high diastereoselectivities were observed with Eu(hfc)3 and magnesium dibromide.Evidence from reactions of Eu(hfc)3 and magnesium dibromide catalysis indicated a possible "chelation-control" pathway.Lewis acid catalysis from diethylaluminum chloride provides products with moderate to high diastereoselectivity.The mechanistic pathway with catalysis by diethylaluminum chloride was less clear.A possible mechanism based upon a "Cram" addition is considered.