Kurzfassung

Abstract:
(Schiff-base)vanadium(V) complexes with tridentate imine-auxiliaries serve as catalysts for the oxidation of Br– with tert-butyl hydroperoxide (TBHP) in non aqueous solvents. This method has been utilized to prepare 5-exo-bromocyclized products from substituted 4-penten-1-ols [i.e. bis(homoallyl) alcohols] in synthetically useful yields. An application of this sequence has been applied to develop a concise synthesis of the 2-epimer of magnosalicin, constituent of Magnolia...Abstract:
(Schiff-base)vanadium(V) complexes with tridentate imine-auxiliaries serve as catalysts for the oxidation of Br– with tert-butyl hydroperoxide (TBHP) in non aqueous solvents. This method has been utilized to prepare 5-exo-bromocyclized products from substituted 4-penten-1-ols [i.e. bis(homoallyl) alcohols] in synthetically useful yields. An application of this sequence has been applied to develop a concise synthesis of the 2-epimer of magnosalicin, constituent of Magnolia salicifolia, starting from (1S*,2S*,3R*)-bis-(2,4,5-trimethoxyphenyl)-2-methyl-4-penten-1-ol. Treatment of bis(homoallylic) alcohols, which have either two methyl groups or one phenyl substitutent located at the terminal position of the olefinic p-bond, with Br–, TBHP and a vanadium(V) catalyst 5 furnished brominated tetrahydropyrans as major products.

According to results from 51V NMR , ESI-MS, and reactivity-selectivity studies, the mechansim of this bromocyclization proceeds in two concise steps. Initially, the primary oxidant TBHP is activated via coordination to a (Schiff-base)vanadium(V)-complex to furnish the corresponding tert-butyl peroxy complex that is able to oxidize Br–. This step provides Br2 as effective bromiating reagent that converts organic stubstrates in a second, non vanadium-dependent step into the derived organobromine compounds.

Leading References:
[1] Bromoperoxidase and Functional Enzyme Mimics for Oxidative Bromination – A Sustainable Synthetic Approach. D. Wischang, O. Brücher, J. Hartung, accepted for publication in Coord. Chem. Rev. angenommen.
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