Total synthesis of (-)-salicylihalamide

A concise total synthesis of the potent cytotoxic marine natural products salicylihalamide A and B (la, b) is reported. Key steps of our approach were the asymmetric hydrogenation reactions of beta-keto esters 18 and 32 catalyzed by [((S)-BINAP)Ru-Cl2]2. NEt3 and the cyclization of the macrolide core by ring closing olefin metathesis (RCM) using the "second-generation" ruthenium carbene complex 24 as the catalyst which bears an imidazol-2-ylidene ligand. The EIZ ratio obtained in this macrocyclization reaction was determined by the protecting groups at the remote phenolic OH group of the cyclization precursor. The elaboration of the resulting cycloalkene 37 into the final target involved a CrCl2-mediated synthesis of vinyliodide 49 which, after deprotection, did undergo a copper-catalyzed cross-coupling process with the (Z,Z)-configurated carboxamide 42 to form the labile enamide moiety of 1. Compound 42 was derived from a palladium-catalyzed Negishi coupling between butynylzinc chloride and 3-iodoacrylate 39 followed by a Lindlar reduction of enyne 40 thus obtained and a final aminolysis of the ester group.     

CH-anion versus anion-π interactions in the crystal and in solution of pentafluorobenzyl phosphonium salts

A series of phosphonium salts with pentafluorobenzyl substituents have been synthesized and were investigated in the crystal as well as in solution. The solid state structures of 1a, 1b and 2d reveal the presence of anion-π as well as CH-anion interactions. The two attractive, yet competitive forces seem to act in concert and a directing effect of the CH interaction on the relative position between anion and π-system is observed. The search for anion-π interactions in solution failed. Only CH-anion interactions proved to be important in solution.     

Synthesis and Photoluminescence Properties of the Red‐Emitting Phosphor Mg3(BN2)N Doped with Eu2+

Mg₃(BN₂)N was prepared by solid state metathesis reactions and several europium (Eu²⁺) doped samples were prepared to discover novel red‐emitting photoluminescent (PL) materials. It turned out that the undoped and doped samples showed very broad deep‐red photoluminescence ranging from about 500 nm into the near infrared. Due to the similar spectra of the undoped and doped samples and unusually high FWHM values of about 5780 cm^–1 we conclude that the luminescence process originates from defect sites. This was confirmed by decay measurements which show that the decay constants for all samples were in the range of several milliseconds.     

Application of P-stereogenic aminophosphine phosphinite ligands in asymmetric hydroformylation

New chiral aminophosphine phosphinite ligands with a stereogenic center at the aminophosphine phosphorus atom were prepared based on (R,S)-ephedrine as the chiral auxiliary and backbone. Substituents at the chiral aminophosphine as well as at the phosphinite phosphorus atom were varied. These new ligands were applied to the rhodium-catalyzed asymmetric hydroformylation of vinyl arenes. The enantiomeric excess reached up to 77%. 1H and 31P NMR studies of the Rh complexes under syngas pressure reveal that [HRh(CO)2(PP)] complexes with the NP* moiety in an axial position are responsible for enantioselectivity.