Silyl Esters as Reactive Intermediates in Organic Synthesis

Abstract

Silyl esters have been exploited as meta-stable 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.

Chiral Bisphosphine-Catalyzed Asymmetric Staudinger/aza-Wittig Reaction: An Enantioselective Desymmetrizing Approach to Crinine-Type Amaryllidaceae Alkaloids

“…Fortunately, this competitive pathway is largely inhibited in practice under the employed reduction conditions [PhSiH 3 , (4-NO 2 C 6 H 4 O) 2 PO 2 H, DIPEA]. Based on some precedents, we assumed that a phosphoric silyl ester species ( III ) should generate in situ, which could effectively differentiate the reduction of PO and PN moieties. This assumption was validated by the time-stacked in situ 31 P NMR study (162 MHz, 85 °C) (Figure ).…”