Diastereofacial selectivity in uncatalyzed Diels-Alder cycloadditions involving α,β-unsaturated esters and lactones with stereogenic centers containing oxygen functiionalities
摘要:
Both experimental and theoretical studies on the Diels-Alder cycloadditions of dienophiles 1, 2 and 3 to different dienes show that the observed diastereofacial selectivity results from a combination of electronic and steric interactions. The traditional Felkin-Anh model is not appropriate for these cases. Several new chiral synthetic building blocks have been prepared.
Rate, and endo/exo and facial diastereostereoselectivity of the title reactions have been highly enhanced under the action of aluminum, among other metals used as catalysts, compared to the thermal processes. EtAlCl2 and Et2AlCl were the reagents that afforded the best results.