期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 21, 期 6, 页码 2339-2342出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201405852
关键词
catalysis; cyclization; electron transfer; titanium; umpolung
资金
- Fonds der Chemischen Industrie
- Deutsche Forschungsgemeinschaft (DFG) [STR 1150/3-1]
A sequence of two titanium(III)-catalyzed reductive umpolung reactions is reported that allows the rapid construction of benzazo- and benzoxozine building blocks. The first step is a reductive cross-coupling of quinolones or chromones with Michael acceptors. This reaction proceeds with complete syn-selectivity for the quinolone functionalization while the anti-diastereomers are obtained as the major products from chromones. With different reaction conditions, the stereochemical outcome can be altered to afford the syn-chromanone products as well. A subsequent reductive ketyl radical cyclization forges the tricyclic title compounds in good yields. A stereochemical model explaining the observed stereoselectivities is provided and the product configurations were unambiguously verified by X-ray analyses and 2DNMR spectroscopic experiments.
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