Long-distance control in stereoselective reduction of 3-[3-(4′-bromo[1,1′-biphenyl]-4-yl)-3-keto-1-phenylpropyl]-4-hydroxy-2H-1-benzopyran-2-one: Relative configuration of prevailing diastereomer and absolute configuration of its enantiomers
✍ Scribed by Amir Avdagić; Livius Cotarca; Zdenko Hameršak; Miklos Hollòsi; Zsuzsa Majer; Edina Ljubović; Andreja Šuste; Vitomir Šunjić
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 254 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0899-0042
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✦ Synopsis
Depending on the reducing agent and reaction conditions, diastereoselective reduction of 3-[3-(4Ј-bromo[1,1Ј-biphenyl]-4-yl)-3-keto-1-phenylpropyl]-4hydroxy-2H-1-benzopyran-2-one (2) proceeds with different stereoselectivity; a surprisingly high, approximately 90% d.e. of 4A is achieved with NaBH 4 in MeOH at low temperature. Resulting diastereomeric racemates 4A and 4B are separated and their respective syn and anti configurations are assigned on the bases of mechanic considerations, supported by the 1 H-NMR spectra and conformational analysis based on MM2 calculations. The syn diastereomer 7A, 4-OMe derivative of 4A, was partially resolved by acylation at C(3)-OH with S-(-)-camphanic acid to camphanyl ester 12 of (-)-7A, leaving (+)-enantiomer 7A. The assignment of absolute 1R,3S-configuration to (-)-7A is based on comparison of its CD spectrum with those of the model compounds S-14 and R-15, which represent partial chromophores 4-hydroxy-2H-1-benzopyran-2-one (4hydroxycoumarin) A, and 4Ј-bromo-1,1Ј-biphenyl B; their exciton coupling in (-)-7A is suggested.