Enantioselective Cleavage of Cyclobutanols Through Ir-Catalyzed C-C Bond Activation: Mechanistic and Synthetic Aspects.

The Ir-catalyzed conversion of prochiral tert-cyclobutanols to β-methyl-substituted ketones proceeds under comparably mild conditions in toluene (45-110 °C) and is particularly suited for the enantioselective desymmetrization of β-oxy-substituted substrates to give products with a quaternary chirality center with up to 95 % ee using DTBM-SegPhos as a chiral ligand. Deuteration experiments and kinetic isotope effect measurements revealed major mechanistic differences to related Rh -catalyzed transformations. Supported by DFT calculations we propose the initial formation of an Ir hydride intermediate, which then undergoes a β-C elimination (C-C bond activation) prior to reductive C-H elimination.

Building up Pt -Thiosemicarbazone-Lysine-sC18 Conjugates.

Three chiral tridentate N^N^S coordinating pyridine-carbaldehyde (S)-N4-(α-methylbenzyl)thiosemicarbazones (HTSCmB) were synthesised along with lysine-modified derivatives. One of them was selected and covalently conjugated to the cell-penetrating peptide sC18 by solid-phase peptide synthesis. The HTSCmB model ligands, the HTSCLp derivatives and the peptide conjugate rapidly and quantitatively form very stable Pt chlorido complexes [Pt(TSC)Cl] when treated with K PtCl in solution.