Silene equivalents through the rhodium-catalysed reactions of α-hypersilyl diazoesters: a computational and experimental study

Abstract

The generation of silenes through the rhodium-catalysed decomposition of α-hypersilyl diazocarbonyl compounds has been explored both computationally and experimentally. This transformation proceeds via a pathway involving initial formation of the carbene, followed by rearrangement, initially to a silene and ultimately to a ketene. Density functional theory (DFT) calculations of model compounds suggested that silene formation was most preferential with electron donating substituents attached to the carbonyl group. The predictions were experimentally evaluated and hypersilyl diazoacetates provided an unusually long-lived species (t_1/2 > 40 h) that reacts as a formal silene equivalent. Further DFT calculations support the formation of an internally stabilised silene in the form of a 1,2-silaoxetene. Importantly the acylsilene–silaoxetene reaction is reversible and consequently this silene equivalent reacts with α,β-unsaturated carbonyl compounds to form cyclic silyl enol ethers which have considerable potential for further synthetic transformations.