期刊
ADVANCED SYNTHESIS & CATALYSIS
卷 349, 期 3, 页码 364-372出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.200600365
关键词
O-acylcyanohydrins; Lewis acids; Lewis bases; salen; titanium
Additions of structurally diverse alpha-ketonitriles to aromatic and aliphatic prochiral aldehydes yielding highly enantioenriched acylated cyanohydrins were achieved using a combination of a titanium salen dimer and an achiral or chiral Lewis base. In most cases high yields and high enantioselectivities were observed. The ee was moderate in the initial part of the reaction but increased over time. This could be avoided, and higher ees obtained, by keeping the titanium complex, in the presence or absence of aldehyde and ketonitrile, at -40 degrees C prior to the addition of the Lewis base. A mechanism initiated by nucleophilic attack of the tertiary amine at the carbonyl carbon atom of the ketonitile is supported by C-13 labelling experiments.
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