Meso methanolysis

Related studies on meso tricyclic anhydrides were published in 1988 and 1990 by Aitken et al. [7, 8]. Their best result was achieved in the methanolysis of the tetracyclic anhydride 6 with (—)-quinine (2) as catalyst (Scheme 13.2 57% yield of the lactone ester 7 with 76% ee). The enantiomeric purity of the tricyclic lactone-ester 7 could be increased significantly (> 99% ee) by subsequent recrystallization in the presence of (—)-quinine (2). 

A very efficient and practical process for desymmetrization of meso-anhydrides was reported by Bolm et al. in 1999 and in subsequent publications (Scheme 13.3) [9, 10]. In their approach, which is a further development and improvement in the use of alkaloids as catalysts, (—)-quinine (2) or (+)-quinidine (3) in this case, low reaction temperature and solvent optimization proved crucial to achieving optimum enantioselectivity. Under their conditions methanolysis of several meso anhydrides (8a-g, 9a-g, Scheme 13.3) can be achieved in good yields and with excellent enantiomeric excesses in the presence of equimolar amounts of the inexpensive and readily available alkaloids 2 and 3 [9, 10]. 

Formation of chiral a-amino acids from aminomalonic acids via decarboxylative protonation is readily accomplished in the presence of thiourea 1 (ex quinidine)/ The diaster-eomeric 2 (ex quinine) has been employed to generate monomethyl esters in chiral form by methanolysis meso-cydic anhydrides ... 

Synthesis of Meso-ionic Thiazoles.—The anhydro-5-hydroxythiazolium hydroxide (43 R = SMe, R = COCF3) is obtained from the reaction between sarcosine, carbon disulphide, methyl iodide, and potassium hydroxide, followed by treatment of the intermediate MeSC(S)NMeCH2C02H (A) with trifluoroacetic anhydride. Methanolysis of (43) gives the methyl ester of the intermediate (A), whilst photolysis yields F3C0CH(C02Me)NMeCS2Me. 

Some uses of sugars in novel resolutions of enantiomers have been reported. The ferrocene derivative 225 could be isolated from reaction of a mixture of d,l-and meso-isomers of the corresponding ferrocene dicarbonyl chloride with methyl 4,6-0-benzylidene-a-D-glucopyranoside. This could then be converted by methanolysis into the enantiomerically-pure (R,/ )-ferrocene derivative 226. When the chiral pyridinium salt 227 was photolysed, equimolar amounts of the diastereomers 228 and 229 were obtained. Although no chirality transfer occurred, the two isomers could be separated after acetylation, and some further chemistry was performed on the fused aziridine ring of one of the dia-... 

Scheme 7.16 Enantioselective methanolysis of meso-anhydride catalyzed by bicyclic tertiary amines 77...

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