Enantioselective Deprotonation/Electrophile Addition Reactions of Tricarbonyl(phenyl carbamate)chromium Complexes

✍ Scribed by Anna Quattropani; Gérald Bernardinelli; E. Peter Kündig

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: German
• Weight: 239 KB
• Volume: 82
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/(sici)1522-2675(19990113)82:1<90::aid-hlca90>3.0.co;2-h

✦ Synopsis

Sequential reaction of the tricarbonyl[(h 6 -phenyl) carbamate]chromium complex 3 with chiral amide bases (see 4 and 5) and electrophiles yielded planar chiral ortho-substituted complexes 6 with up to 70% enantiomeric excess (ee) (Scheme 2, Table 1 and2). The enantiomer purity could be increased to b 90% ee by fractional crystallization. In all but one case the racemate crystallized selectively, leaving the enantiomerically enriched complex in solution. X-Ray crystal-structure analyses of rac-6a and (1R )-6a suggest that this can be ascribed to a more favorable packing of enantiomers of opposite configuration in the solid state than that of the enantiomerically pure solid. Increasing the temperature of the intermediate ortho-lithiated aryl carbamate complex induced an anionic ortho-Fries rearrangement: The 1,3-transposition of the carbamoyl group yielded the ortho-substituted (h 6 -benzamide)tricarbonylchromium complexes 10 in 65% yield, after exposure to the electrophile ( Scheme 6), and the use of a chiral amide base 5 in the deprotonation step afforded the product with an ee of 54%.