Silyl Esters as Reactive Intermediates in Organic Synthesis

Silyl esters have been exploited as metastable reaction intermediates, both purposefully and unintentionally, since at least the 1960s. Their reactivity is broadly related to the substituents on the silicon, and in this way their properties can be readily modulated. Silyl esters have unique reactivity profiles that have been used to generate downstream products of a range of functionalities, and because of this many excellent methods for the synthesis of a variety of value-added chemicals have been developed. Furthermore, because of the frequent use of hydrosilanes as terminal reductants in catalytic processes, silyl ester intermediates are likely more commonly utilized by synthetic chemists than currently realized. This review comprehensively summarizes the reactions known to take advantage of reactive silyl ester intermediates and discusses examples of catalytic reactions that proceed in an unanticipated manner through silyl ester intermediates. 1 Introduction 2 Synthesis of Silyl Esters 3 Making Amides from Silyl Esters 3.1 Amidation Using Chlorosilanes 3.2 Amidation Using Azasilanes 3.3 Amidation Using Oxysilanes 3.4 Amidation Using Hydrosilanes 3.5 Amine Formation via Amidation/Reduction 3.6 Miscellaneous 4 Mechanistic Investigations of Amidation 4.1 Mechanism of Amidation Using Chlorosilanes 4.2 Mechanism of Amidation Using Hydrosilanes 4.3 Mechanism of Amidation Using Oxy- or Azasilanes 5 Making Esters from Silyl Esters 6 Making Aldehydes, Alcohols, Amines, and Alkanes via Reduction 6.1 Aldehyde Synthesis by Metal-Free Reduction 6.2 Aldehyde Synthesis by Metal-Mediated Reduction 6.3 Alcohol Synthesis by Metal-Mediated Reduction 6.4 Amine Synthesis 6.5 Alkane Synthesis by Metal-Free Reduction 7 Making Acid Chlorides from Silyl Esters 8 In Situ Generated Silyl Esters and Ramifications for Catalysis 9 Conclusion