Silica Gel Stabilized Na and Na/K Alloys: Highly Effective, Versatile and Environmentally Friendly Reducing Agents

摘要

Na and Na/K alloys in the liquid phase can be absorbed into amorphous silica gel at loadings up to 40 wt%. Further heating of these so-called stage 0 materials at 150 or 400 degrees C furnishes stage I and stage II materials, respectively, as free-flowing powders that can be handled under much safer conditions than the corresponding starting materials. Stage I Na and Na2K possess valuable reducing properties and they have found a variety of low impact applications in organic synthesis, including, e.g., the reductive deprotection of several functional groups, the development of safer protocols to operate the Bouveault-Blanc and the Birch reductions, and a new and particularly efficient approach to the Grignard and Darzens reactions. 1 Introduction 2 Reductive Deprotection Procedures 3 Bouveault-Blanc Reduction of Esters 4Ammonia-Free Birch Reductions 5 Synthesis of Alkyldiaryl- and Dialkylarylphosphines 6 C-C Bond Forming Reactions 7 Further Applications 8 Conclusion