School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Angew Chem Int Ed Engl. 2017 Feb 13;56(8):2127-2131. doi: 10.1002/anie.201611273. Epub 2017 Jan 18.
Homologation of readily available α-boryl pyrrolidines with metal carbenoids is especially challenging even when good leaving groups (Cl ) are employed. By performing a solvent switch from Et O to CHCl , efficient 1,2-metalate rearrangement of the intermediate boronate occurs with both halide and ester leaving groups. The methodology was used in the total synthesis of the Stemona alkaloid (-)-stemaphylline in just 11 steps (longest linear sequence), with high stereocontrol (>20:1 d.r.) and 11 % overall yield. The synthesis also features a late-stage lithiation-borylation reaction with a tertiary amine containing carbenoid.
即使使用良好的离去基团（Cl），将易得的α-硼基吡咯烷与金属卡宾物进行对应物认可也极具挑战性。通过从 EtO 到 CHCl3 的溶剂转换，带有卤素和酯离去基团的中间硼酸酯都能有效地发生 1,2-金属重排。该方法在 Stemona 生物碱（-）-延胡索乙素的全合成中仅用 11 步（最长线性序列），以高立体选择性（>20:1 d.r.）和 11%的总收率实现。该合成还具有带有叔胺的卡宾物的晚期锂化-硼化反应。
