Facile Construction of the Tricyclo[5.2.1.01,5]decane Ring System by Intramolecular Double Michael Reaction: Highly Stereocontrolled Total Synthesis of (±)-8,14-Cedranediol and (±)-8,14-Cedranoxide

It was observed that the synthesis of tricyclo[5.2.1.0 1,5 ]decane 10 can be performed effectively by the intramolecular double Michael reaction of 5-(5-methoxycarbonyl-4-pentenyl)-2-cyclopenten-1-one ( 9 ). Highly stereocontrolled total syntheses of (±)-8,14-cedranediol ( 2 ) and (±)-8,14-cedranoxide ( 1 ) were accomplished by the application of this methodology. Heating 5-(1,5-dimethyl-5-ethoxycarbonylpent-4-enyl)-2-cyclopenten-1-one ( 15 ) with TMSCl, Et 3 N, and ZnCl 2 in o -dichlorobenzene at 150 °C provided (±)-(1 R *,2 R *,5 R *,6 R *,7 S *)-2,6-dimethyl-6-ethoxycarbonyltricyclo[5.2.1.0 1,5 ]-decan-9-one ( 16 ) as a single isomer. The product 16 was stereoselectively converted into the above cedranoids 2 and 1 through ring expansion chemistry.