Catching elusive glycosyl cations in a condensed phase with HF/SbF₅ superacid

International audienceGlycosyl cations are universally accepted key ionic intermediates in the mechanism of glycosylation, the reaction that covalently links carbohydrates to other molecules. These ions have remained hypothetical species so far because of their extremely short life in organic media as a consequence of their very high reactivity. Here, we report the use of liquid hydrofluoric acid-antimony pentafluoride (HF/SbF5) superacid to generate and stabilize the glycosyl cations derived from peracetylated 2-deoxy and 2-bromoglucopyranose in a condensed phase. Their persistence in this superacid medium allows their three-dimensional structure to be studied by NMR, aided by complementary computations. Their deuteration further confirms the impact of the structure of the glycosyl cation on the stereochemical outcome of its trapping

Iridium-Catalyzed Silylation

In this chapter, homogeneous iridium-catalyzed silylation reactions are reviewed, focusing primarily on their synthetic utility. Additionally, relevant catalytic cycles are commented, paying especial attention to those that are more representative of each type of process. The chapter is divided into two main types of reactions, namely, hydrosilylation and C–H bond silylation. The former deals with the hydrosilylation of polar unsaturated bonds (ketones and imines) and non-polar unsaturated bonds (alkenes and alkynes). The latter covers the directed and non-directed C–H bond silylation of alkenes, alkynes, arenes, and alkanes – mainly comprising dehydrogenative silylation reactions, which may occur in the presence or absence of a hydrogen acceptor.This work was supported by the “Ramón y Cajal” program (RYC2016-20864) (FSE/Agencia Estatal de Investigación) (M. I.) and the Spanish Ministry of Science, Innovation and Universities (RTI2018-099136-A-I00).Peer reviewe