Ring meso-anhydrides

Narasaka et al. demonstrated the utility of titanium-ligand complexes in the resolution of chiral a-aryl esters [52]. Ti(Oi-Pr)4-ligand 56 complex resolves 2-pyridine thioesters with high selectivities (fcrei=26-42, see Scheme 13). Seebach and co-workers have examined titanium-TADDOLate complexes as reagents for the ring opening of meso anhydrides, dioxolanones, and azalactones [53]. Addition of an achiral isopropoxide source renders the desymmetrization of meso... 

Type II catalytic asymmetric acyl transfer processes have been most extensively developed for the case of ASD of meso-anhydrides by nucleophilic ring-opening with alcohols, and so these processes will be the first type II processes considered here. 

In many instances, the tetranaphthyl-substituted diol, the preparation of which is described here, gave the most effective chiral titanium catalysts. Three examples are the nucleophilic addition of diethylzinc to aldehydes (eq 1),10 the Diels-Alder reaction of 3-crotonoyl-1,3-oxazolidin-2-one to cyclopentadiene (eq 2),7 and the ring opening of a meso anhydride to a half ester (eq 3).11... 

C. Bolm, I. Schiffers, C.L Dinter, A. Gerlach, Practical and highly enantioselective ring opening of cyclic meso-anhydrides mediated by cinchona alkaloids, J. Org. Chem. 65 (21) (2000) 6984-6991. 

Enantioselective alcoholysis of racemic, prochiral, or meso cyclic anhydrides can be catalyzed by hydrolases, yielding the corresponding monoesters (Eigure 6.25). In most cases, the enantioselectivity was moderate ]75-77]. Organometallic catalysts or organocatalysts such as cinchona alkaloids are often more efficient than enzymes for the stereoselective ring opening of cyclic anhydrides. 

Stereoselective ring cleavage and monoesterification of chiral Meldrum s acid derivatives has been achieved in high yield with a 34% enantiomeric excess under phase-transfer catalytic conditions in the presence of A-benzylquininium chloride [29]. A similar asymmetric ring-opening of prochiral (meso) acid anhydrides with... 

There has been considerable interest in the stereoselective ring opening of meso-cyclic anhydrides. The stereoselective alcoholysis of these anhydrides is particularly attractive as the resulting hemiesters are used as versatile intermediates in the construction of many bioactive compounds [1], Much effort has, therefore, been devoted to the development of efficient enzymatic and nonenzymatic catalytic systems for this reaction [2], Among the stereoselective catalysts developed to date,... 

Catalytic enantioselective reductive desymmetrisation of achiral and meso-compounds, in particular, transformations of imides to lactams or lactones, anhydrides to lactones, and ring-opening of oxacycfic rings 13CC10666. 

Scheme 10.10 Ring-opening reaction of meso-glutaric anhydrides with alcohols.

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