Regioselective preparation of tricyclic terpene ring systems by cycloaddition of 1,3,3-trimethyl-2-vinylcyclohexene with unsymmetrical quinones

Synthesis of the hexacyclic triterpene core of the jujuboside saponins via tandem Wolff rearrangement-intramolecular ketene hetero-Diels-Alder reaction

The jujubosides are saponin natural products reported to have immunoadjuvant, anticancer, antibacterial, antifungal, and antisweet activities. The triterpene component, jujubogenin contains a unique tricyclic ketal motif comprising the DEF ring system. Herein, we describe our efforts toward the total synthesis of jujubogenin, using a sterically-demanding intermolecular Diels-Alder reaction to assemble the C-ring and a tandem Wolff rearrangement-intramolecular ketene hetero-Diels-Alder reaction to form the DF-ring system. Acid-catalyzed cyclization of the resulting bicyclic enol ether then closes the E-ring to provide the hexacyclic core of jujubogenin.

Microwave-assisted Diels–Alder reaction of 1,3,3-trimethyl-2-vinyl-1-cyclohexene with chromones — An expeditious approach to analogues of the puupehenone group of marine diterpenoids and kampanols

A rapid assembly of the tetracyclic core of marine diterpenoids related to puupehenone and kampanols by a Diels–Alder reaction of 1,3,3-trimethyl-2-vinyl-1-cyclohexene with chromones under microwave irradiation with or without TiCl4 is described.