Lewis acid-catalyzed intoamolecular [2+2] cycloaddition of α -ester-substituted conjugated dienyl- and trienylphosphonates. New synthesis of functionalized cyclic terpenoids

摘要

α-Ester-substituted 1,3-dienylphosphonates 7 and 8, prepared by the Knoevenagel condensation, underwent intramolecular [2+2] cycloaddition in the presence of Lewis acid to form bicyclo[4.2.0] (26-57/100 yield) and bicyclo[3.2.0]skeleton (14-38/100 yield), respectively. Similar treatment of homologous 1,3-dienylphosphonate 11 and 1,3,5-trienylphosphonate 12 resulted in the formation of ionone derivatives (30-94/100 yield). The intramolecular cycloaddition reaction was applicable to several conjugated dienes bearing an ester group.