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Photochemical Deracemization of Allenes and Subsequent Chirality Transfer.

ABSTRACT: Trisubstituted allenes with a 3-(1'-alkenylidene)-pyrrolidin-2-one motif were successfully deracemized (13 examples, 86-98?% ee) employing visible light (?=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).

SUBMITTER: Plaza M

PROVIDER: S-EPMC7537568 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Photochemical Deracemization of Allenes and Subsequent Chirality Transfer.

Plaza Manuel M Jandl Christian C Bach Thorsten T

Angewandte Chemie (International ed. in English) 20200602 31

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 enantiom ...[more]

PMID: 32390291

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