RuCl₃/CeCl₃/NaIO₄:  A New Bimetallic Oxidation System for the Mild and Efficient Dihydroxylation of Unreactive Olefins

Abstract

[reaction: see text] The catalytic dihydroxylation of olefins represents a unique synthetic tool for the generation of two C,O-bonds with defined relative configuration. Whereas OsO(4) has been established as a very general dihydroxylation catalyst within the past 30 years, the less expensive and toxic isoelectronic RuO(4) has found only limited use for this type of oxygen-transfer reaction. High catalyst loading and undesired side reactions were severe drawbacks in RuO(4)-catalyzed oxidations of C,C-double bonds. Recently, we were able to improve the RuO(4)-catalyzed dihydroxylation by addition of Bronsted acids to the reaction mixture. This protocol proved to be of general applicability, however, certain limitations were observed. To address these problematic functional groups a new Lewis acid accelerated oxidation was developed. The use of only 10 mol % of CeCl(3) allowed a further decrease in the catalyst concentration down to 0.25 mol % while broadening the scope of the reaction. Silyl ethers and nitrogen containing functional groups are now tolerated in this optimized protocol. Furthermore, competing scission reactions are supressed in the presence of Lewis acid allowing longer reaction times and the successful oxidation of electron-deficient tetrasubstituted double bonds that cannot be oxidized using known dihydroxylation protocols.

Novel Synthesis of 1-substituted meso-3,4-dihydroxypyrrolidines with a RuCl3-catalyzed Key Reaction

“…1) by analogy of Plietker's method (use of catalytic amounts of RuCl 3 and CeCl 3 as Lewis acid) which was successfully applied to cyclic olefins [16]. Although N-phenyl-3-pyrrolidine (4a) was obtained smoothly in two steps from (Z)-but-2-ene-1,4-diol (1) in good yield [20], no product formation in the Ru-catalyzed cis-dihydroxylation reaction of N-phenyl-3-pyrrolidine (4a) was observed.…”

“…cis-Dihydroxylation of (Z)-but-2-ene-1,4-diyl dimethanesulfonate (2) [16]: NaIO 4 (12.8 g, 60 mmol) and CeCl 3 (0.99 g, 4 mmol) were added to distilled water (18 mL) and the mixture was gently heated at 50-60 °C until a bright yellow suspension was formed (ca. 10 min).…”

“…be suppressed by addition of Lewis acids to the system to promote the hydrolysis of the Ru-diester [15,16]. A study on the effects of various Lewis acids showed that CeCl 3 as additive in the dihydroxylations of olefins resulted in high yields and the best diol-aldehyde ratio [16].…”

“…A study on the effects of various Lewis acids showed that CeCl 3 as additive in the dihydroxylations of olefins resulted in high yields and the best diol-aldehyde ratio [16]. Ru nanoparticles immobilized on hydroxyapatite [18], or a polymer incarcerated ruthenium catalyst [19] allowed recovery of the catalyst and rendered the reactions easy-to-perform and more economical.…”

Synthesis of Fused Oxa‐Aza Spiro Sugars from D‐Glucose‐Derived δ‐Lactone as Glycosidase Inhibitors

“…[19] Epoxidation of olefin 14 using m-chloroperbenzoic acid [20a] and H 2 O 2 in the presence of formic acid [20b] was also unsuccessful. To overcome this problem we chose a highly reactive bimetallic oxidizing system [21] (RuCl 3 /CeCl 3 ·7H 2 O/NaIO 4 ) for the cisdihydroxylation of olefin 14. Thus, the reaction of olefin 14 with RuCl 3 (0.25 mol-%) in the presence of CeCl 3 ·7H 2 O/ NaIO 4 in an EtOAc/CH 3 CN/H 2 O mixed solvent system at 0°C followed by acetylation of the obtained α-diol gave acetate 15 in 62 % overall yield.…”