Diisobutylaluminum hydride-promoted cyclization of benzyl and phenylsilyl ethers bearing a 2-(trimethylsilyl)ethynyl group: syntheses of indenes and benzosiloles

Diisobutylaluminum Hydride Promoted Cyclization of 1-Hydrosilyl-4-silyl-1,3-enynes to Polysubstituted Siloles

“…In the course of our study on synthetic uses of DIBAL-H, we found that the treatment of 1,3-enyne 1a , bearing a hydrosilane moiety, with DIBAL-H gave silole 2a (Table ). With this finding, our goal was set to develop a new method for silole synthesis by the DIBAL-H-promoted cyclization.…”

“…The capture of ( E )- 2e′ and the time variations of the reaction of 1e suggest that the reaction mechanism involves hydroalumination of the alkynylsilane moiety of 1 with DIBAL-H, geometrical isomerization of the initially formed alkenylalanes A to B , , and subsequent intramolecular silicon–carbon bond formation (Scheme ). Since triorganosilyl groups at the sp-carbon are known to promote alkyne hydroalumination and geometrical isomerization of the resulting alkenylalanes, , the essential role of the alkynylsilane moiety for the present cyclization (Scheme ) agrees with the proposed mechanism. Unlike the reaction of 1e , the formation of alkenylalane ( E )- 2a′ from 1a was not detected even at the time when 1a was not fully converted (Table , entry 5).…”

Recent Advances in the Synthesis of Indenes

“…Miura reported that the reaction of o ‐[2‐(trimethylsilyl)ethynyl]benzyl methyl ethers 137 with diisobutylaluminum hydride (DIBAL‐H) in octane at 100 °C gave 2‐(trimethylsilyl)indenes 138 in good to excellent yields (Scheme ). This cyclization proceeds by regio‐ and stereoselective hydroalumination of the alkyne moiety followed by intramolecular nucleophilic substitution.…”