Positive Cooperative Effect in Ion-Pair Recognition by a Tris-urea Hemicryptophane Cage.

The synthesis of a hemicryptophane cage combining a CTV unit with a C3 symmetrical moiety bearing three urea functions is reported. This host was found to bind anions with higher binding constants than other previously reported hemicryptophanes. Due to its heteroditopic character this cage proved to be an efficient ion-pair receptor. The best cooperativity effect was observed for the tetramethylammonium bromide (TMABr) salt, which was confirmed and rationalized by DFT calculations.

Bare histidine-serine models: implication and impact of hydrogen bonding on nucleophilicity.

A new family of 2-hydroxyalk(en/yn)ylimidazoles has been evaluated as serine-histidine bare dyad models for the ring-opening reaction of L-lacOCA, a cyclic O-carboxyanhydride. These models were selected to unravel the implication of intramolecular hydrogen bonding and to substantiate its influence on the nucleophilicity of the alcohol moiety, as it is suspected to occur in enzyme active sites. Although designed to exclusively facilitate the preliminary step of proton transfer during the studied ring-opening reaction, these minimalistic models depicted a measureable increase in reactivity relative to the isolated fragments. A couple of reliable experimental and theoretical methods have been developed to readily monitor the strength of the intramolecular hydrogen bond in dilute solution. Results show that the folded conformers are the most nucleophilic species because of the intramolecular hydrogen bond.

Platinum(II)-coordinated phosphinous acid-catalyzed alkylidenecyclopropanation of bicyclic alkenes with terminal alkynes.

New Pt(eta2-acetato){[(R)(Ph)PO]2H} complexes 3 prepared from PtCl2(CH3CN)2 and secondary phosphine oxides (SPOs) catalyzed the [2+1] cycloaddition of phenylethyne (5a) with norbornene derivatives 4 to afford benzylidenecyclopropanes.

Highly selective cobalt-mediated [6 + 2] cycloaddition of cycloheptatriene and allenes.

[6 + 2] Cycloadditions between cycloheptatrienes with allenes have been investigated. Cobalt salts were found to promote this transformation efficiently. Moreover, this reaction was found to be highly selective since only one regioisomer was obtained with an excellent E/Z-selectivity.