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キーワード:
Alkinmetathese; Cycloisomerisierung; Goldkatalyse; Molsieb; Nitrido-Molybdän-Komplex
要旨:
A new generation of user-friendly and highly active alkyne metathesis (pre)catalysts has been developed. These nitride complexes of molybdenum can be easily prepared in large quantity from inexpensive sodium molybdate. Triphenylsilanolate was found to be the optimal ancillary ligand, as it provides the catalyst with a remarkable activity as well as an exceptional functional group tolerance. The catalyst was rendered fully air stable by complexation with bidentate nitrogen donor ligands like 1,10-phenanthroline. The structures of representative examples of this new generation of alkyne metathesis catalysts in the solid state were determined by x-ray analysis. These adducts are per se catalytically inactive in alkyne metathesis reactions but can easily be reactivated by decomplexation in the presence of weak lewis acids like MnCl2. The addition of molecular sieves (5 Å) to the reaction mixture removes the byproduct 2-butyne (generated when using methyl-capped alkynes) from the equilibrium and thereby significantly improves the chemical yields and the reaction rates. The scope of the newly developed system could be demonstrated by the application to a number of representative alkyne metathesis reactions. The developed methods grant improved access to cyclic alkynes by ring-closing alkyne metathesis (RCAM). Therefore, gold-catalyzed cycloisomerisation reactions of such cyclic alkynes were studied, attempting to identify new routes for the preparation of biologically active natural products.
