Asymmetric catalysis dihydroxylation

Unlike the impressive progress that has been reported with asymmetric catalysis in other additions to alkenes (i.e., the Diels-Alder cycloaddition, epoxidation, dihydroxylation, aminohydroxylation, and hydrogenation) so far this is terra incognita with nitrile oxide cycloadditions. It is easy to predict that this will become a major topic in the years to come. 

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... 

The Nobel Prize in Chemistry 2001 was awarded to three researchers for their pioneering work in the field of asymmetric catalysis. One of them, K. Barry Sharpless, was honored for the epoxidations named after him (Section 3.4.6). The second reason for the award was his development of the asymmetric dihydroxylation (AD Figure 17.21). The Sharpless reactions that were honored with the Nobel Prize have three things in common first, they are oxidations, second, they are catalytic asymmetric syntheses, and third, they owe their high enan-tiocontrol to the additive control of stereoselectivity. In the introductory passages to... 

With cis-vic-aminohydroxylations of unsymmetrical alkenes, however, it may be a problem that two regioisomers occur—a complication that does not occur with cis-vic-dihydroxylations. The addition of (DHQ)2-PHAL or (DHQD)2-PHAL (Figure 17.21, part I) in a cis-vic-aminohydroxylation will also cause asymmetric catalysis. The related reactions are known as asymmetric aminohydroxylations. 

This collection begins with a series of three procedures illustrating important new methods for preparation of enantiomerically pure substances via asymmetric catalysis. The preparation of 3-[(1S)-1,2-DIHYDROXYETHYL]-1,5-DIHYDRO-3H-2.4-BENZODIOXEPINE describes, in detail, the use of dihydroquinidine 9-0-(9 -phenanthryl) ether as a chiral ligand in the asymmetric dihydroxylation reaction which is broadly applicable for the preparation of chiral dlols from monosubstituted olefins. The product, an acetal of (S)-glyceralcfehyde, is itself a potentially valuable synthetic intermediate. The assembly of a chiral rhodium catalyst from methyl 2-pyrrolidone 5(R)-carboxylate and its use in the intramolecular asymmetric cyclopropanation of an allyl diazoacetate is illustrated in the preparation of (1R.5S)-()-6,6-DIMETHYL-3-OXABICYCLO[3.1. OJHEXAN-2-ONE. Another important general method for asymmetric synthesis involves the desymmetrization of bifunctional meso compounds as is described for the enantioselective enzymatic hydrolysis of cis-3,5-diacetoxycyclopentene to (1R,4S)-(+)-4-HYDROXY-2-CYCLOPENTENYL ACETATE. This intermediate is especially valuable as a precursor of both antipodes (4R) (+)- and (4S)-(-)-tert-BUTYLDIMETHYLSILOXY-2-CYCLOPENTEN-1-ONE, important intermediates in the synthesis of enantiomerically pure prostanoid derivatives and other classes of natural substances, whose preparation is detailed in accompanying procedures. 

Marko, I. E., Svendsen, J. S. Dihydroxylation of carbon-carbon double bonds. Comprehensive Asymmetric Catalysis l-lll 1999, 2, 713-787. Bolm, C., Hildebrand, J. P., Muniz, K. Recent advances in asymmetric dihydroxylation and aminohydroxylation. Catal. Asymmetric Synth. (2nd Edition) 2000, 399 28. 

One of the most exciting developments in asymmetric catalysis over the past 25 years has been the discovery of transition metal complexes that catalyze the oxidation of alkenes to chiral epoxides and 1,2-diols. Equations 12.16, 12.17, and 12.18 show examples of epoxidation and 1,2-dihydroxylation. 

These furfliryl alcohols can be produced in either enantiomeric form via asymmetric catalysis. Our preferred method for the asymmetric synthesis of these fiiran alcohols 4.2 is by the highly enantioselective Noyori reduction of achiral acylfurans 4.1 (Scheme 4). Alternatively fiirfurly alcohols like 4.4 can be prepared by the Sharpless asymmetric dihydroxylation of vinylfuran 4.3. Key to this later approach was the recognition that vinylfuran 4.3 could be made by a Petersen olefination reaction. 

The asymmetric dihydroxylation of alkenes (the AD reaction) using osmium catalysts was discovered and developed by Sharpless, and now represents one of the most impressive achievements of asymmetric catalysis. The majority of early results did not use catalytic systems however, a breakthrough in the catalytic asymmetric dihydroxylation reaction was reported by Sharpless and coworkers in 1988. 

Besides the more common reactions such as hydrogenation, isomerization, alkylation, and the Diels-Alder reaction. Sharpless epoxidation and dihydroxylation by asymmetrical catalysis are rapidly emerging as reactions with immense industrial potential. Table 9.7 lists some important syntheses based on asymmetric catalysis. These include processes for the pharmaceutical drugs (S)-naproxen, (S)-ibuprofen, (,S)-propranolol, L-dopa, and cilastatin, a fragrance chemical, L-menthol, and an insecticide (/ )-disparlure. Deltamethrin, an insecticide, is another very good example of industrial asymmetric synthesis. The total synthetic scheme is also given for each product. In general, the asymmetric step is the key step in the total synthesis, but this is not always so, as in the production of ibuprofen. Many of the processes listed in the table are in industrial production. 

The aim of this review is to discuss the contribution of soluble polymer-supported ligands and insoluble polymer-supported ligands to asymmetric catalysis in the field of reduction of C=0 bonds, cyclopropanation, Diels-Alder, alkylation, allylation, dihydroxylations,... 

In the presence of a chiral amine such as quinine, Sharpless has demonstrated asymmetric catalysis for this dihydroxylation reaction that is also accelerated by this type of ligand. The oxidizing agent (oxygen donor) is then amine oxide. This system compares with Jacobsen s efficient hydrolytic kinetic resolution shown in section 4, but extension to the industrial scale is more problematic with the Sharpless system. 

Coupled redox systems have also been successfully employed in asymmetric catalysis. Krief and coworkers were the first to use air as a terminal oxidant with the Sharpless dihydroxylation catalyst by using benzyl phenyl selenide as a photosensitizer [32-34]. The dihydroxylation of a-methylstyrene using the selenide sensitizer decreases the oxidant waste by over 50-fold compared to the standard oxidation conditions using AD-Mix (KsFelCNJg is the terminal oxidant in AD-Mix) with similar enantiomeric excess and yield [34]. This example of a coupled reaction showcases the potential waste reduction provided by this approach. 

A more versatile method to use organic polymers in enantioselective catalysis is to employ these as catalytic supports for chiral ligands. This approach has been primarily applied in reactions as asymmetric hydrogenation of prochiral alkenes, asymmetric reduction of ketone and 1,2-additions to carbonyl groups. Later work has included additional studies dealing with Lewis acid-catalyzed Diels-Alder reactions, asymmetric epoxidation, and asymmetric dihydroxylation reactions. Enantioselective catalysis using polymer-supported catalysts is covered rather recently in a review by Bergbreiter [257],... 

About a decade after the discovery of the asymmetric epoxidation described in Chapter 14.2, another exciting discovery was reported from the laboratories of Sharpless, namely the asymmetric dihydroxylation of alkenes using osmium tetroxide. Osmium tetroxide in water by itself will slowly convert alkenes into 1,2-diols, but as discovered by Criegee [15] and pointed out by Sharpless, an amine ligand accelerates the reaction (Ligand-Accelerated Catalysis [16]), and if the amine is chiral an enantioselectivity may be brought about. 

Since the first two approaches are very well known and exploited, and excellent reviews and books on the topic are available [1], we will deal only with some of the most recent findings in chemical catalysis -excluding the Sharpless asymmetric epoxidation and dihydroxylation, to which the whole of Chapter 10 is devoted. Synthetic catalysts which mimic the catalytic action of enzymes, known as chemzymes, will be also considered. 

Important extensions of proline catalysis in direct aldol reactions were also reported. Pioneering work by List and co-workers demonstrated that hydroxy-acetone (24) effectively serves as a donor substrate to afford anfi-l,2-diol 25 with excellent enantioselectivity (Scheme 11) [24]. The method represents the first catalytic asymmetric synthesis of anf/-l,2-diols and complements the asymmetric dihydroxylation developed by Sharpless and other researchers (described in Chap. 20). Barbas utilized proline to catalyze asymmetric self-aldoli-zation of acetaldehyde [25]. Jorgensen reported the cross aldol reaction of aldehydes and activated ketones like diethyl ketomalonate, in which the aldehyde... 

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