Palladium dihydroxylation

Amino-Hydroxylation. A related reaction to asymmetric dihydroxylation is the asymmetric amino-hydroxylation of olefins, forming v/c-ami noalcohols. The vic-hydroxyamino group is found in many biologically important molecules, such as the (3-amino acid 3.10 (the side-chain of taxol). In the mid-1970s, Sharpless76 reported that the trihydrate of N-chloro-p-toluenesulfonamide sodium salt (chloramine-T) reacts with olefins in the presence of a catalytic amount of osmium tetroxide to produce vicinal hydroxyl p-toluenesulfonamides (Eq. 3.16). Aminohydroxylation was also promoted by palladium.77... 

Unlike palladium(II), osmium tetraoxide and ruthenium tetraoxide catalyze the dihydroxylation of one or both double bonds of an allene. The osmium tetraoxide-catalyzed dihydroxylation of unsymmetrically substituted allenes 45 can lead to two different a-ketols, 46 and 47, depending on which of the double bonds is oxidized. David et al. studied this reaction using NMO as a stoichiometric oxidant and found good product selectivity in a few cases, but the yields were only moderate (Scheme 17.15) [16]. They showed that the most substituted double bond was oxidized preferably when the bulkiness of the allene substituents did not interfere. 

Recently, a bifunctional, silica gel-supported catalyst, containing an alkaloid ligand 14d and a palladium(0)complex, was applied to the dihydroxylation of disubstituted alkenes formed in situ from aryl iodides and terminal alkenes in a single-pot procedure [72]. 

Full details for the palladium-catalyzed cyclization of 3,4-alkadienoic acids to 7-methylene-A -butenolides have been given (Equation 49) <2005T9896>. a-Substituted 7-alkylidene A -butenolides are also available in good yield by palladium-catalyzed carbonylative cyclization of /3-iodo enones <2005TL8137>. In asymmetric de novo syntheses of D- and L-talose, iterative asymmetric dihydroxylation reactions of dienoates have been employed to furnish 7-substituted A -butenolides <2005JOC10576>. 

In addition to the functionalization protocols of Schemes 13 and 14, vinylic substitution reactions involving metalation and palladium-mediated carbon-carbon bond formation have been formulated," which further broaden the variety of stmctural types available from the Patemo-BUchi reaction. For example, deprotection and stannylation of photoaldol (133), followed by refimctionalization of the a-enol ether position of vinylstannane (134), gave the substituted oxetane (135) in good overall yield. Similar functionalization of bicyclic oxetane (136) via exo-face dihydroxylation and acid-catalyzed reorganization of the acetal to the protected 3-deoxy-( )-streptose (137) has been reported, which illustrates the synthetic utility of such processes in the synthesis of polyoxygenated materials." ... 

The allylic amination with benzylamine or related amines such as (3,4-dimethoxy-phenyl)methylamine catalyzed by palladium coordinated with the dihydroxylated ferrocenylphosphine 8b takes place with high enantioselectivity (Scheme 2-30) [27]. Thus, reaction of l,3-diphenyl-2-propenyl ethyl carbonate 41 with benzylamine gives a quantitative yield of allylic amination product 42 with > 97% ee. High enantioselectivity is also obtained in the allylic amination of 2-propenyl esters 43 substituted... 

Several enantioselective approaches to vitamin E (1), based on resolution of the products, the use of enantiopure natural building blocks, auxiliary controlled reactions and asymmetric oxidations have been described. In addition, a palladium-catalyzed asymmetric allylic alkylation reaction to build up the chiral chroman framework has been employed by Trost. Tietze and coworkers have developed asymmetric syntheses of the chiral chroman moiety using either the selective ally-lation of an alkyl methyl ketone or a Sharpless dihydroxylation as the key step. However, none of these methods is efficient enough for an industrial approach. ... 

The use of C2-symmetric aziridines as chiral auxiliaries has been reviewed by Tanner <94AG(E)599>. Chiral A-acylaziridines such as (143) have been used in enolate chemistry (see Section 1.01.8.2). Aziridine-containing ligands such as (144) have been used for a variety of metal-catalyzed reactions such as the asymmetric dihydroxylation of alkenes, the palladium-catalyzed allylation of nucleophiles, asymmetric cyclopropanation, and aziridination <94AG(E)599,94TL4631). 

This de novo approach to carbohydrates has also been applied to oligosaccharides (Schemes 9 to 14). Key to the success of this approach is the development of a mild palladium-catalyzed glycosylation (Scheme 6) in combination with the use of the previously developed highly stereoselective enone reduction and dihydroxylation reaction (Scheme 3) as post-glycosylation transformation for the installation of manno stereochemistry 19). 

Keinan prepared separately the two fragments (the THF moiety and the Y-methyl-y-lactone) and used, as a key step of his sequence, the asymmetric dihydroxylation (AD-mix.-p), the very efficient Sharpless procedure for the formation of a,(3-diols. Then, the cross-coupling was performed by addition of an alkyne and a vinyl halide in the presence of palladium and copper catalysts (Fig. 6). Treatment of the unsaturated ester 48 (prepared in 4 steps from commercially available starting material, and 65 % overall yield) with AD-mix.-p in rerr-butanol/water (1 1) with methanesulfonamide for 16 h at 0 °C afforded the lactone 49 which possessed 3 carbon atoms out of the 4 with the desired absolute configuration. Inversion of the fourth stereocentre after acetonide... 

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