Substitution-Dependent Ring-Opening Hydrosilylation or Dehydrogenative Hydrosilylation of Cyclopropyl Aldehydes and Ketones Catalyzed by Au Nanoparticles

Abstract

The reaction between hydrosilanes and arylsubstituted cyclopropyl aldehydes or ketones catalyzed by Au nanoparticles supported on TiO 2 provides two distinct ringopening reaction motifs depending on the substituents. 2-Arylsubstituted cyclopropyl carbonyl compounds form linear enol ethers via formal silyl hydride addition on the carbon atom bearing the aryl group. Under the reaction conditions, the hydrosilylation adducts undergo hydrolytic silyl deprotection to form acyclic aldehydes or ketones. For 2,2-arylalkyl-or 2,2-diaryl-substituted cyclopropyl carbonyl compounds, a ring-opening dehydrogenative hydrosilylation pathway is solely observed yielding chromatographically stable silyloxy-1,3-dienes. In the presence of 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO), the reaction is inhibited, indicative of a radical pathway. The proposed intermediate αcyclopropyl silyloxy radicals undergo radical-clock ring-opening to form benzyl radicals, which may either be captured by the hydrosilane H atom (for 2-aryl-substituted substrates) to form linear silyl enol ethers or eliminate H 2 and form silyloxy-1,3-dienes in the case of the bulkier 2,2-disubstituted ones.