School of Chemistry, University of Tasmania, Hobart, Australia.
Beilstein J Org Chem. 2008 Jan 15;4:3. doi: 10.1186/1860-5397-4-3.
The Birch reduction of electron rich pyrroles does not occur readily. However, dissolving metal reduction with zinc under acidic conditions gives 3-pyrrolines (2,5-dihydropyrroles) in reasonable yield. This dissolving metal reduction was first reported by Knorr and Rabe in 1901 but since then has only been reported for the reduction of electron rich pyrroles.
The partial reduction of bicyclic alpha-ketopyrrole derivatives has been performed under dissolving metal conditions with zinc and hydrochloric acid to give excellent yields of hexahydroindolizidines. This reduction method has been utilised for the diastereoselective synthesis of 5-alkylindolizidines and the stereoselectivity obtained is opposite to that of catalytic hydrogenation.
An efficient stereoselective synthesis of indolizidine alkaloids has been developed from alpha-ketopyrrole intermediates using a modified version of Knorr and Rabe's pyrrole reduction.
富电子吡咯的伯奇还原不易发生。然而，在酸性条件下用锌进行溶解金属还原可得到 3-吡咯啉（2,5-二氢吡咯），收率合理。这种溶解金属还原最早由 Knorr 和 Rabe 在 1901 年报道，但此后仅报道了富电子吡咯的还原。
在锌和盐酸的溶解金属条件下对双环α-酮吡咯衍生物进行部分还原，可得到六氢吲哚嗪的优异收率。这种还原方法已用于 5-烷基吲哚嗪的非对映选择性合成，并且获得的立体选择性与催化氢化的相反。
从α-酮吡咯中间体出发，通过对 Knorr 和 Rabe 的吡咯还原的改进版本，开发了一种高效立体选择性的吲哚嗪生物碱合成方法。
