Reduction of Acetals with TiCl4–LiAlH4

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Abstract
The reduction of dialkyl acetals derived from aromatic aldehydes and ketones with TiCl4–LiAlH4 in THF or diethyl ether at room temperature afforded the coupling products, pinacol ethers or olefins, in high yields. On the other hand, when acetals derived from aliphatic aldehydes and ketones were treated with TiCl4–LiAlH4 in diethyl ether, the reductive dealkoxylation took place and the corresponding ethers were isolated in good yields. As to the reaction mechanism we propose that Ti(II) is the reactive species in reductive coupling reaction of acetals derived from aromatic aldehydes and ketones, and that Ti(0)–H2AlCl complex may be the reactive species in reductive dealkoxylation of acetals derived frcm aliphatic aldehydes and ketones.

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