Stereoselective total syntheses of Limazepine E and Barmumycin, potent, naturally occurring antitumor agents, are described. The total syntheses control the olefin geometry via a highly selective chelation-controlled Ireland-Claisen rearrangement of a seven-membered lactone-derived boron enolate for the synthesis of (E)-4-ethylidene proline, a crucial building block for a number of natural products.

Stable pre-ligands and common metal salts provide, via β-carbon elimination, access to Cp-metal complexes suitable for in situ catalyst preparation.

Chiral cyclopentadienyl (Cp x ) group 9 metal complexes have become versatile catalysts for a variety of efficient enantioselective C−H functionalizations. Atropchiral binaphthyl-derived Cp x ligands having tuning options at the 3,3′-positions present a robust choice of catalyst, giving high enantioselectivities and good reactivities. Herein, we report streamlined syntheses of binaphthyl backbone Cp x ligands that feature new substituents at the 3,3′-positions: namely, trimethylsilyl, I, and Br. We introduce as well Cp x ligands with a new atropchiral MeO-biphenyl backbone. All ligands are smoothly complexed with rhodium(I) salts. The Cp x Rh I complexes obtained were systematically mapped by X-ray crystal analysis in order to collect steric parameters that might guide a rational selection of the chiral Cp x ligand for enantioselective reactions. The catalytic performances of the complexes were evaluated by two Rh III -catalyzed C−H functionalizations as benchmark transformations. In both cases, a simpler to access ligand provided superior reactivity and enantioselectivity. Additionally, related Cp x Co III and Cp x Ir III complexes equipped with the developed ligands were prepared and characterized. Article pubs.acs.org/Organometallics

A formal total synthesis of pyrrolo[1,4]benzodiazepine anticancer antibiotic family member limazepine E is described. The synthesis features a stereoselective introduction of a trisubstituted double bond using novel sterically demanding Julia-Kocienski reagents, allowing the number of linear steps to be significantly reduced. The potential of the newly developed reagents has also been demonstrated by the formal total synthesis of barmumycin.