Selective Preparation of Benzyltitanium Compounds by the Metalative Reppe Reaction. Its Application to the First Synthesis of Alcyopterosin A

Dialkoxytitanacyclopentadienes, prepared from two different acetylenes and a divalent titanium alkoxide reagent, Ti(O-i-Pr)4/2 i-PrMgCl, reacted with propargyl bromide to give directly benzyltitanium compounds. The resultant benzyltitanium compounds underwent deuteriolysis, iodinolysis (with I2), or oxygenation (with O2 gas) to give the corresponding deuterium-labeled compounds, iodides, or alcohols, illustrating their synthetic versatility. The first synthesis of alcyopterosin A, a bicyclic aromatic sesquiterpenoid recently isolated and characterized, has been achieved by this method, starting with an appropriate combination of an acetylene and a diyne.