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Racemic seven-membered lactones

CHMO is known to catalyze a number of enantioselective BV reactions, including the kinetic resolution of certain racemic ketones and desymmetrization of prochiral substrates [84—87]. An example is the desymmetrization of 4-methylcyclohexanone, which affords the (S)-configurated seven-membered lactone with 98% ee [84,87]. Of course, many ketones fail to react with acceptable levels of enantioselectivity, or are not even accepted by the enzyme. [Pg.50]

A large number of mono- and bicyclic lactones (73-91) have been obtained by using pig liver esterase in combination with horse liver esterase for the enantiomer-differentiating hydrolysis of the corresponding racemic lactones. Interestingly, in the series of methyl-substituted lactones (85-89), both enzymes show toward the seven-membered lactone (86) the opposite enantiomer selectivity as compared to the other lactones. [Pg.383]

The ketal 215 was hydrolysed with pyridinium tosylate and the ketoalcohol reduced stereoselectively to the anti 1,3-diol 216 (antbsyn = 96 4) using Evans s method (58). The C-6 and C-8 hydroxyl groups were differentiated by formation of the seven-membered lactone 217 using Mukaiyama s method (59). The minor enantiomer of the lactone 217 was largely removed because the racemate crystallised, thereby improving the e.e. from 92% to >99%. The 8-hydroxy group was... [Pg.251]

Lipase catalysis is often used for the enantioselective production of chiral compounds indeed, lipase has been known to induce an enantioselective ROP of racemic lactones. In the lipase-catalyzed polymerization of racemic j8-butyrolactone (/3-BL), the enantioselectivity was low rather, an enantioselective polymerization of /3-BL occurred by employing a thermophilic lipase to yield the (R)-enriched polymer with 20-37% enantiomeric excess (e.e.) [101]. The enantioselectivity was greatly improved by copolymerization with seven- or 13-membered nonsubstituted lactones, using the lipase CA catalyst, whereby the e.e.-value reached almost 70% for the copolymerization of /3-BL with DDL [102]. It should be noted that, in the case of the lipase CA catalyst, the (S)-isomer was reacted preferentially to produce the (S)-enriched, optically active copolymer. The lipase CA-catalyzed copolymerization of i5-CL (six-membered) with DDL proceeded enantioselectively, to yield the (R)-enriched optically active polyester with an e.e.-value of 76%. [Pg.691]


See other pages where Racemic seven-membered lactones is mentioned: [Pg.163]    [Pg.366]    [Pg.163]    [Pg.366]    [Pg.201]    [Pg.190]    [Pg.251]    [Pg.368]    [Pg.241]    [Pg.200]    [Pg.756]    [Pg.756]    [Pg.443]    [Pg.756]    [Pg.735]   


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Racemic lactones

Seven-membered

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