No abstract

alpha-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% yield) and bicyclo[3.2.0]skeleton (14-38% 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% yield). The intramolecular cycloaddition reaction was applicable to several conjugated dienes bearing an ester group.

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Lewis Acid-Catalyzed Intramolecular [2 + 2] Cycloaddition of α-Ester-Substituted Conjugated Dienyl-and Trienylphosphonates. New Synthesis of Functionalized Cyclic Terpenoids. -The intramolecular cycloaddition is also applied to conjugated dienes bearing two ester groups. The cycloadduct (IVa) can easily be transformed into the sesquiterpene (VII) having a novel type of carbon skeleton and the adducts (XII), (XIII) and (XIV) are versatile intermediates for the synthesis of retinol derivatives. -(OKAUCHI, T.; KAKIUCHI, T.; KITAMURA, N.; UTSUNOMIYA, T.; ICHIKAWA, J.; MINAMI, T.; J.