Enantiodivergent oxidation

Figure 37 Enantiodivergent oxidation of geranyl iV-phenylcarbamate by A. niger.

Table 9.4 Mutagenesis of CHMOAcineto toward enantiodivergent Baeyer-Villiger oxidations.

Parallel to the modification of the catalytic performance in Baeyer-Villiger oxidations, random mutagenesis was successfully applied to improve the stereoselectivity of CHMOAcineto hi cascs of essentially racemic sulfoxide formation. In addition, enantiodivergent clones with >98% ee for both antipodal products were identified (Table 9.5) [205]. However, improvement in stereoselectivity of mutant enzymes was often accompanied by increased formation of sulfone. This effect can also be utilized to resolve racemic sulfoxides. 

T. Hudlicky, H. Luna, J. D. Price, and F. Rulin, An enantiodivergent approach to d- and L-erythrose via microbial oxidation of chlorobenzene, Tetrahedron Lett. 1989,... 

F. Rulin, Microbial oxidation of chloro-aromatics in the enantiodivergent synthesis of pyrrolizidine alkaloids trihydroxyhelio-tridanes,/. Org. Chem. 1990, 55, 4683-4687. 

Scheme 2.164 Enantiodivergent microbial Baeyer-Villiger oxidation involving nonclassic resolution...

In a separate communication, Kita and coworkers also reported an enantiodivergent synthesis of an ABODE ring analog of the antitumor antibiotic fredericamycin A via an intramolecular [4 + 2] cycloaddition. Late-stage oxidations were performed on the di-f-butylsilylene for protection of phenolic hydroxyl groups. Syntheses of both (R)- and (5)-enantiomers were reported (eq 18). ... 

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