The unique reactivity of "super silyl" in organic synthesis: A theoretical study

Abstract

We recently developed a new use of the super silyl group in organic reactions, and showed that it has unique reactivity. One of the reactions using this reagent is diastereoselective Mukaiyama aldehyde cross-aldol reaction catalyzed by a highly active Bronsted acid. This reaction produced syn-1,3-diol derivatives with high yield and high stereoselectivity. Certain features and outcomes of the reaction were not clear, so we decided to investigate the reaction mechanism through a theoretical study. In this paper, structures of super silyl species were observed as the subject of study. First 1 and 2 were investigated so that the effect of a TMS group adjacent to a silicenium ion could be determined. Interestingly, it was found that the TMS group stabilized the silicenium ion. It is presumed that the stability of the tris(trimethylsilyl) silicenium ion (TTMSS+) is related to the unique reactivity of super silyl group in theses reactions. We also investigated equivalent structures of silyl enol ethers (SEE) and found an unusual structure of 5. This structure is a result of unusual interactions between the silyl portion and enol ether (EE) portion; 1) C=C and Si-Si bonds, 2) lone pair of oxygen and Si-Si bond.