Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 59, Issue 31, Pages 12785-12788Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202004797
Keywords
allenes; chiral resolution; enantioselectivity; hydrogen bonds; photochemistry; sensitizers
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Funding
- Deutsche Forschungsgemeinschaft [Ba 1372/24-1]
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Trisubstituted allenes with a 3-(1 '-alkenylidene)-pyrrolidin-2-one motif were successfully deracemized (13 examples, 86-98 % ee) employing visible light (lambda=420 nm) and a chiral triplet sensitizer as the catalyst (2.5 mol %). The photocatalyst likely operates by selective recognition of one allene enantiomer via hydrogen bonds and by a triplet-sensitized racemization process. Even a tetrasubstituted allene (45 % ee) and a seven-membered 3-(1 '-alkenylidene)-azepan-2-one (62 % ee) could be enantiomerically enriched under the chosen conditions. It was shown that the axial chirality of the allenes can be converted into point chirality by a Diels-Alder (94-97 % ee) or a bromination reaction (91 % ee). Ring opening of the five-membered pyrrolidin-2-one was achieved without significantly compromising the integrity of the chirality axis (92 % ee).
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