cis-2,6-Bis-(methanolate)-piperidine oxovanadium(V) complexes as catalysts for oxidative alkenol cyclization by tert-butyl hydroperoxide

• Stereoselective synthesis of cis-2,6-bis-(hydroxymethyl)-piperidines.
• Structural characterization of piperidine-derived vanadium(V) complexes.
• Chemoselective and rapid hydroperoxide activation by new vanadium(V)-complexes.
• Improved chemical inertness of vanadium(V)-based oxidation catalysts.
• Enantioselective epoxidation of geraniol catalyzed by a chiral vanadium(V)-complex.

cis-2,6-Bis-(methanolate)-piperidine oxovanadium(V) complexes are Lewis acids able to catalyze oxidative cyclization of alkenols by tert-butyl hydroperoxide (TBHP). Terminal dimethyl-substituted (prenyl-type) 4-pentenols bearing an alkyl or a phenyl group in position 1 afford under such conditions 2,5-cis-derivatives of 2-(tetrahydrofuran-2-yl)-2-propanol as major and tetrahydropyran-3-ols as minor products (four examples). Oxidizing 1-phenyl-6-methylhept-5-en-1-ol yields a 75/25-mixture of the derived 2-(tetrahydropyran-2-yl)-2-propanol and an oxepan-3-ol, whereas 2-propenols give epoxides in up to 94% yield. Epoxidizing geraniol by TBHP in the presence of a vanadium catalyst prepared from (2S,6R)-2-diphenylmethanol-6-hydroxymethylpiperidine occurs enantioselectively. Highfield shifts of vanadium-51 resonances upon adding alkyl hydroperoxides to solutions of cis-2,6-bis-(methanolate)-piperidine vanadium(V) complexes point to vanadium(V) tert-butyl peroxy complex formation as key step for activating peroxides.

cis-2,6-Bis-(methanolate)-piperidine oxovanadium(V) complexes catalyze oxidative cyclization of alkenols by tert-butyl hydroperoxide (TBHP) via intermediate peroxy vanadium(V) complexes.Figure optionsDownload as PowerPoint slide