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Photochemical Deracemization of Allenes and Subsequent Chirality Transfer
Author(s) -
Plaza Manuel,
Jandl Christian,
Bach Thorsten
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202004797
Subject(s) - allene , chirality (physics) , racemization , chemistry , axial chirality , photochemistry , enantiomer , stereochemistry , enantioselective synthesis , catalysis , organic chemistry , physics , chiral symmetry breaking , quantum mechanics , nambu–jona lasinio model , quark
Trisubstituted allenes with a 3‐(1′‐alkenylidene)‐pyrrolidin‐2‐one motif were successfully deracemized (13 examples, 86–98 % ee ) employing visible light ( λ =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 ).