An efficient stereocontrolled route to ( )-cylindricine C is described. Reaction of 9-hydroxynon-1-en-5one oxime with 2,3-bis(phenylsulfonyl)-1,3-butadiene affords a 7-oxa-1-azanorbornane cycloadduct in high yield. The formation of the bicyclic isoxazolidine arises from conjugate addition of the oxime onto the diene to give a transient nitrone that spontaneously undergoes an intramolecular dipo...

[figure: see text] Thermolysis of lactone 18 initiated a stereospecific transannular nitrone-olefin [3 + 2] cycloaddition to yield tetracycle 19. Methanolysis followed by reductive cleavage of the isoxazolidine yielded 20, representing the azaspirocyclic core of pinnaic acid (1).

Intramolecular transannular dipolar cycloaddition was investigated as a key step in a synthetic approach to the core of the sarain alkaloids; although the use of an azomethine ylide was unsuccessful with the chosen aldehyde substrate, cycloaddition with a nitrone did give the alternative regioisomeric bridged cycloadduct.

The stereoselective synthesis of penmacric acid, an optically active C-4 substituted pyroglutamic acid, has been efficiently achieved through an unusual 11-step sequence starting from simple N-triisopropylsilylpyrrole. The key-steps are the initial addition of the pyrrole nucleus onto a chiral nitrone and the obtention of the pyroglutamic acid moiety by reductive hydrogenation of the pyrrole fo...

between the charge distribution of the amide bond and the fluoroalkene moiety, as well as their dipole moments. Therefore, a monofluoroalkene moiety can be used as a peptidomimetic unit in the design of protease inhibitors; this type of rigid isostere of the peptidic bond can facilitate the cis/ trans conformational control of the replaced peptidic fragment. Numerous synthetic endeavors have be...