Olefin dihydroxylation, catalytic asymmetric

Subsequently, stoichiometric asymmetric aminohydroxylation was reported.78 Recently, it was found by Sharpless79 that through the combination of chloramine-T/Os04 catalyst with phthalazine ligands used in the asymmetric dihydroxylation reaction, catalytic asymmetric aminohydroxylation of olefins was realized in aqueous acetonitrile or tert-butanol (Scheme 3.3). The use of aqueous rerr-butanol is advantageous when the reaction product is not soluble. In this case, essentially pure products can be isolated by a simple filtration and the toluenesulfonamide byproduct remains in the mother liquor. A variety of olefins can be aminohydroxylated in this way (Table 3.1). The reaction is not only performed in aqueous medium but it is also not sensitive to oxygen. Electron-deficient olefins such as fumarate reacted similarly with high ee values. 

The major breakthrough in the catalytic asymmetric dihydroxylation reactions of olefins was reported by Jacobsen et al.55 in 1988. Combining 9-acetoxy dihydroquinidine as the chiral auxiliary with /V-methylmorphine TV-oxide as the secondary oxidant in aqueous acetone produced optically active diols in excellent yields, along with efficient catalytic turnover. 

Along with catalytic asymmetric epoxidation, the related dihydroxylation of olefins is another venerable catalytic enantioselective process that is widely used by the modern organic chemist. An application of this important transformation may be found in Corey s 1994 preparation of optically pure 109 (Scheme 16), an intermediate in Corey s 1985 total synthesis of ovalicin.1181 The catalytic asymmetric dihydroxylation that affords 108 solves one of the most challenging problems in the total synthesis installment of the tertiary alcohol center with the appropriate relative and absolute stereochemistry. 

SCHEME 178. Osmium-catalyzed catalytic asymmetric dihydroxylation of olefins by H2O2 as terminal oxidant... 

Success in the use of Ti tartrate catalyzed asymmetric epoxidation depends on the presence of the hydroxyl group of the allylic alcohol. The hydroxyl group enhances the rate of the reaction, thereby providing selective epoxidation of the allylic olefin in the presence of other olefins it also is essential for the achievement of asymmetric induction. The role played by the hydroxyl group in this reaction is described in a later section of this chapter. The need for a hydroxyl group necessarily limits the scope of this asymmetric epoxidation to a fraction of all olefins. Fortunately, allylic alcohols are easily introduced into synthetic intermediates and are very versatile in organic synthesis. The Ti tartrate catalyzed asymmetric epoxidation of allylic alcohols has been applied extensively as documented in the literature and in this review. The development of methods aimed at catalytic asymmetric epoxidation of unfunctionalized olefins is described in Chapter 6B, whereas the catalytic asymmetric dihydroxylation of olefins, which provides an alternate method for olefin functionalization, is described in Chapter 6D. 

The cis dihydroxylation of olefins mediated by osmium tetroxide represents an important general method for olefin functionalization [1,2]. For the purpose of introducing the subject of this chapter, it is useful to divide osmium tetroxide mediated cis dihydroxylations into four categories (1) the stoichiometric dihydroxylation of olefins, in which a stoichiometric equivalent of osmium tetroxide is used for an equivalent of olefin (2) the catalytic dihydroxylation of olefins, in which only a catalytic amount of osmium tetroxide is used relative to the amount of olefin in the reaction (3) the stoichiometric, asymmetric dihydroxylation of olefins, in which osmium tetroxide, an olefinic compound, and a chiral auxiliary are all used in equivalent or stoichiometric amounts and (4) the catalytic, asymmetric dihydroxylation of olefins. The last category is the focus of this chapter. Many features of the reaction are common to all four categories, and are outlined briefly in this introductory section. 

This brief outline of historical developments in osmium tetroxide-mediated olefin hydroxy-lation brings us to our main subject, catalytic asymmetric dihydroxylation. The transition from stoichiometric to catalytic asymmetric dihydroxylation was made in 1987 with the discovery by Sharpless and co-workers that the stoichiometric process became catalytic when N-methyl-... 

The focus of this chapter is to acquaint the reader with details of catalytic asymmetric dihydroxylation with osmium tetroxide and the scope of results that one can expect to achieve with current optimum conditions. The literature through mid-1992 has been reviewed in compiling this chapter. Osmium tetroxide catalyzed hydroxy]ations of olefins and acetylenes are the subject of an extensive review by Schroder published in 1980 [2a]. A comprehensive review of research and industrial applications of asymmetric dihydroxylations is in preparation [2b]. 

D.3. CATALYTIC ASYMMETRIC DIHYDROXYLATIONS BY OLEFIN SUBSTITUTION PATTERN... 

Figure 20 Fundamental steps in the commercial catalytic asymmetric dihydroxylation of olefins catalyzed by osmium tetroxide.

Ionic solvents have been used to facilitate the Heck reaction (13-9), the oxidation of alcohols with hypervalent iodine reagents (19-3)," and the catalytic asymmetric dihydroxylation of olefins (15-48) using a recoverable and reusable osmium/... 

Bolm, C., Gerlach, A. Polymer-supported catalytic asymmetric Sharpless dihydroxylations of olefins. Eur. J. Org. Chem. 1998, 21-27. 

Shibata, T., Gilheany, D. G., Blackburn, B. K., Sharpless, K. B. Ligand-based improvement of enantioselectivity in the catalytic asymmetric dihydroxylation of dialkyl-substituted olefins. Tetrahedron Lett. 1990, 31, 3817-3820. 

Pini, D., Petri, A., Salvador , P. Heterogeneous catalytic asymmetric dihydroxylation of olefins a new polymeric support and a process improvement. Tetrahedron 99A, 50,11321-11328. 

The time has come for me to discover something new, but there is so much chemistry out there With these words Barry Sharpless closed the Merck-Schuchhardt lecture 1995 in Gottingen, Germany [1]. After about 10 years of continuous optimization, the asymmetric dihydroxylation (AD) of olefins had developed into one of the most versatile catalytic asymmetric reaction to date [2]. 

Sharpless also introduced the catalytic asymmetric dihydroxylation of cis-disubstituted olefins with osmium tetroxide. Jacobsen s catalyst, mentioned earlier, is also much used in synthesis. 

The Sharpless catalytic asymmetric dihydroxylation of olefins, using catalytic amounts of osmium tetroxide in the presence of chinchona alkaloid derivatives, allowed access to a variety of enantiomerically pure 1,2-diols Scheme 3.6.1). 

The first asymmetric synthesis of (20 S)-camptothecin using catalytic asymmetric induction was achieved by Fang et al. in 1994 [74], They carried out a catalytic enantioselective synthesis of Comins s intermediate (23) in order to avoid the use of the expensive chiral auxiliary, 8-phenylmenthol, or similar compound. Intramolecular Heck reaction of pyridine derivative (26) gave the cyclic olefins (27) and (28) in a ratio 1 8. The allylic ether (27) can be isomerized to (28) upon treatment with Wilkinson s catalyst [75], Asymmetric Sharpless dihydroxylation of (28) proceeded successfully when 2,5-diphenyl-4,6-bis(9-0-dihydroquinidyl)pyrimidine [(DHQD)2-PYR] was used as the chiral catalyst [76], and subsequent oxidation gave (29) in 94% ee. Treatment of (29) with acid gave the target molecule (23, Scheme 2.5), which was converted to (20S)-camptothecin in 2 steps using the Comins s procedure [73]. 

Nan1997 Nandanan, E., Sudalai, A. and Ravindranathan, T., New Polymer Supported Cinchona Alkaloids for Heterogeneous Catalytic Asymmetric Dihydroxylation of Olefins, Tetrahedron Lett., 38 (1997) 2577-2580. 

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