Schumacher Christian, Ward Jas S, Rissanen Kari, Bolm Carsten, Aly Mohamed Ramadan El Sayed
Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany.
University of Jyvaskyla, Department of Chemistry, P.O. Box 35, 40014 Jyväskylä, Finland.
Beilstein J Org Chem. 2023 Jan 27;19:91-99. doi: 10.3762/bjoc.19.9. eCollection 2023.
Cholesterol reacts under Appel conditions (CBr/PPh) 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 Δ π-electrons. In contrast, the subsequent azidolysis (NaN/DMF) of 3β-bromocholest-5-ene proceeds predominantly by Walden inversion (S2) 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 , , 1922-1932 and the , , 505-517.
胆固醇在阿佩尔条件下（CBr₄/PPh₃）反应，生成3,5 - 胆甾二烯（消除反应）和3β - 溴胆甾 - 5 - 烯（构型保持的取代反应）。因此，由于Δ π电子的参与，胆固醇的溴化反应偏离了标准阿佩尔机理的立体化学。相反，3β - 溴胆甾 - 5 - 烯随后的叠氮化反应（NaN₃/DMF）主要通过瓦尔登翻转（Sₙ2）进行，生成3α - 叠氮胆甾 - 5 - 烯。所有相关产物的结构通过X射线单晶结构分析得以揭示，核磁共振数据与报道的数据一致。鉴于这些发现，我们在此纠正了我们其中一人在1922 - 1932年以及505 - 517中先前报道的立体化学归属。
