Chiral hemiester

Subsequently, Bolm developed a variant of this process which employed just a sub-stoichiometric quantity of cinchona alkaloid [203], In this method, 10 mol% of quinidine was nsed in conjunction with a stoichiometric amount of pempidine to prevent seqnestration of the cinchona alkaloid by the acidic hemiester product. The chiral hemiester products derived from various meio-anhydrides were obtained with >74% ee and >94% yields (Table 9) [203],... 

Scheme 6.145 Chiral hemiesters obtained from the 121-catalyzed methanolic desymmetrization of cyclic meso-anhydrides.

If required, the interconversion of a given chiral hemiester product into its mirror-image enantiomer can be achieved by a simple two-step protection-deprotection... 

MeOH (0.122 mL, 3.0 mmol) was added dropwise to a stirred suspension of anhydride 57b (164 mg, 1.0 mmol) and quinidine (0.357 g, 1.1 mmol) in a mixture of toluene and tetra-chloromethane (1/1, 5 mL) at -55 °C under argon. The reaction mixture was stirred at this temperature for 60 h. During this period, the material gradually dissolved. Subsequently, the resulting clear solution was concentrated in vacuo to dryness, and the residue was dissolved in EtOAc. The solution was washed with 2N HCl and, after phase separation, followed by extraction of the aqueous phases with EtOAc the organic layer was dried (MgSO ), filtered and concentrated in vacuo to provide the corresponding hemiester (2//,35)-3-endo-methoxycarbonyl-bicyclo[2.2.1]hept-5-ene-2-endo-carboxylic acid as a white solid (192 mg, 98%, 99% ee by chiral-HPLC on the methyl 4-bromophenol diester). 

The first enantioselective organocatalytic oxo-Michael reaction to enones was reported by Falck [109]. Falck developed the intramolecular addition of boronic acids hemiesters to enones catalyzed by thiourea catalysts. Alkyl, aryl, and heteroaryl y-hydroxy enones react with phenylboronic acid to furnish the corresponding boronic hemiesters 118, which after oxidative cleavage of the resulting dioxaboro-lane renders the chiral 1,2 diols 119 in excellent yields and enantioselectivities (Scheme 33.34). 

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