Synthesis of the Bicyclo[7.3.0]dodecatrienediyne Core of the C-1027 Chromophore

Deoxygenation of Oxiranes by λ3 σ3 -Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study

The deoxygenation of parent and substituted oxiranes by λ3 σ3 -phosphorus reagents has been explored in detail, therefore unveiling mechanistic aspects as well as regio- and stereochemical consequences. Attack to a ring C atom is almost always preferred over one-step deoxygenation by direct P-to-O attack. In most cases a carbene transfer occurs as first step, leading to a phosphorane and a carbonyl unit that thereafter react in the usual Wittig fashion via the corresponding λ5 σ5 -1,2-oxaphosphetane intermediate. Betaines rarely constitute true minima after the first C-attack to oxiranes, at least in the gas-phase. Use of the heavier derivatives AsMe3 and SbMe3 as oxirane deoxygenating reagents was also mechanistically studied. The thermodynamic tendency of λ3 σ3 -phosphorus reagents to act as oxygen (O-attack) or carbene acceptors (C-attack) was theoretically studied by means of the thermodynamic oxygen-transfer potential (TOP) and the newly defined thermodynamic carbene-transfer potential (TCP) parameters, that were explored in a wider context together with many other acceptor centres.

Stereoselective Synthesis of the Benzodihydropentalene Core of the Fijiolides

An efficient stereoselective synthesis of the enantiomer of the benzodihydropentalene core of fijiolides A and B has been achieved. The asymmetric conjugate addition of styrylboronic acid to an indenone produced the first stereocenter. Ring C was installed by ring-closing metathesis of a cis disubstituted indanone. Regioselective epoxide opening by NaSePh and subsequent oxidative elimination produced an allylic alcohol. The final introduction of the cyclopentadiene was possible by elimination of an in situ formed triflate.

Total synthesis and related studies of large, strained, and bioactive natural products

Our chemical syntheses and related scientific investigations of natural products with complex architectures and powerful biological activities are described, focusing on the very large 3 nm-long polycyclic ethers called the ciguatoxins, highly strained and labile chromoprotein antitumor antibiotics featuring nine-membered enediyne cores, and extremely potent anthelmintic macrolides called the avermectins.