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Revisiting the bromination of 3β-hydroxycholest-5-ene with CBr₄/PPh₃ and the subsequent azidolysis of the resulting bromide, disparity in stereochemical behavior

Christian Schumacher, Jas S. Ward, Kari Rissanen, Carsten Bolm and Mohamed Ramadan El Sayed Aly

Beilstein J. Org. Chem. 2023, 19, 91–99. https://doi.org/10.3762/bjoc.19.9

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Supporting Information File 1: X-ray crystallography and NMR spectra.
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Revisiting the bromination of 3β-hydroxycholest-5-ene with CBr₄/PPh₃ and the subsequent azidolysis of the resulting bromide, disparity in stereochemical behavior

Christian Schumacher, Jas S. Ward, Kari Rissanen, Carsten Bolm and Mohamed Ramadan El Sayed Aly

Beilstein J. Org. Chem. 2023, 19, 91–99. https://doi.org/10.3762/bjoc.19.9

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Schumacher, C.; Ward, J. S.; Rissanen, K.; Bolm, C.; Aly, M. R. E. S. Beilstein J. Org. Chem. 2023, 19, 91–99. doi:10.3762/bjoc.19.9

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TY  - JOUR
A1  - Schumacher, Christian
A1  - Ward, Jas S.
A1  - Rissanen, Kari
A1  - Bolm, Carsten
A1  - Aly, Mohamed Ramadan El Sayed
T1  - Revisiting the bromination of 3β-hydroxycholest-5-ene with CBr4/PPh3 and the subsequent azidolysis of the resulting bromide, disparity in stereochemical behavior
JF  - Beilstein Journal of Organic Chemistry
PY  - 2023///
VL  - 19
SP  - 91
EP  - 99
SN  - 1860-5397
DO  - 10.3762/bjoc.19.9
PB  - Beilstein-Institut
JA  - Beilstein J. Org. Chem.
UR  - https://doi.org/10.3762/bjoc.19.9
KW  - Appel reaction
KW  - azidolysis
KW  - cholesterol
KW  - crystal structure
KW  - Walden inversion
N2  - Cholesterol reacts under Appel conditions (CBr4/PPh3) to give 3,5-cholestadiene (elimination) and 3β-bromocholest-5-ene (substitution with retention of configuration). Thus, the bromination of cholesterol deviates from the stereochemistry of the standard Appel mechanism due to participation of the Δ5 π-electrons. In contrast, the subsequent azidolysis (NaN3/DMF) of 3β-bromocholest-5-ene proceeds predominantly by Walden inversion (SN2) affording 3α-azidocholest-5-ene. The structures of all relevant products were revealed by X-ray single crystal structure analyses, and the NMR data are in agreement to the reported ones. In light of these findings, we herein correct the previous stereochemical assignments reported by one of us in the Beilstein J. Org. Chem. 2015, 11, 1922–1932 and the Monatsh. Chem. 2018, 149, 505–517.
ER  -

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