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(+)‐Mannolide C is a complex hexacyclic C20 cephalotane‐type diterpenoid featuring a highly strained 7/6/6/5 tetracyclic core containing eight consecutive stereocenters and two bridging lactones. The first asymmetric total synthesis of (+)‐mannolide C has been accomplished by lipase‐mediated resolution, Ru‐complex‐catalyzed double ring‐closing metathesis (RCM) reactions, NiII‐catalyzed diastereoselective Michael addition, and MnIII‐catalyzed allylic oxidation as the key transformations. [ABSTRACT FROM AUTHOR]

Described herein is the first asymmetric total synthesis of (+)-harringtonolide, a natural diterpenoid with an unusual tropone imbedded in a cagelike framework. The key transformations include an intramolecular Diels-Alder reaction and a rhodium-complex-catalyzed intramolecular [3+2] cycloaddition to install the tetracyclic core as well as a highly efficient tropone formation. [ABSTRACT FROM AUTHOR]

We have developed an asymmetric route to (-)-aphanorphine from O-Me-d-tyrosine methyl ester hydrochloride salt, available from d-tyrosine in four steps. The tricyclic framework of (-)-aphanorphine was assembled stereoselectively by intramolecular Friedel-Crafts reaction of the corresponding bicyclic precursor, which was in turn generated via ring-closing metathesis reaction. [ABSTRACT FROM AUTHOR]

Abstract: We describe the efficient formal syntheses of both natural (−)-aphanorphine and unnatural (+)-aphanorphine from the same commercially available amino acid, (2S,4R)-4-hydroxyproline. The tricyclic framework was constructed by intramolecular Friedel–Crafts reaction. (1R,4S)-1-Methyl-8-methoxy-3-(4-toluenesulfonyl)-2,3,4,5-tetrahydro-1,4-methano-3-benzazepine (8) was synthesized in six steps from sulfonamide 3; (−)-aphanorphine methyl ether 24 was obtained in seven steps from lactone 10. Intramolecular etherification of 18 proceeded with excellent stereoselectivity in the presence of BF3·OEt2, which has paved an efficient synthetic route to a series of medicinally attractive heterocycles. [Copyright &y& Elsevier]