Kinetic Control and Locoselectivity in the Electrophilic Cleavage of Allylic Aluminum Compounds: Reactions of Acenaphthenylaluminum Reagents with Carbonyl Substrates

Article abstract of DOI:10.1021/jo00198a011

The benzylic reagent 1-acenaphthenyldiisobutylaluminum, which is formed by the addition of diisobutylaluminum hydride to acenaphthylene, exhibits a 1H NMR spectrum at 25 deg C consistent with a C1-Al bond.At 110 deg C the carbon-aluminum bond undergoes configurational inversion, as evidenced by the magnetic equivalence of the cis and trans C2 protons.At -78 deg C this aluminum compound reacts with ketones to give, upon hydrolysis, 65-75percent of 3-(α-hydroxy-disubstituted methyl)-1,3-dihydroacenaphthylenes, which undergo acid-catalyzed isomerization to 3-(α-hydroxy-disubstituted methyl)acenaphthenes and which dissociate into acenaphthene and the ketone upon contact with Pd.On the other hand, the same reagents at 80-100 deg C lead to the formation of 75-85percent of 1-(α-hydroxy-disubstituted methyl)acenaphthenes.Similiar reactions with acyl chlorides (RCOCl, where R = Me, Et, Ph) and with Me3SiCl laed to 3-acylacenaphthenes and 1-(trimethylsilyl)acenaphthene, respectively.The stereochemically defined adduct of acenaphthylene and diisobutylaluminum deuteride, (cis-2-deuterio-1-acenaphthenyl)diisobutylaluminum diethyl etherate, is found to react with 9-fluorenone at 65 deg C to yield a 1:1 mixture of cis- and trans-2-deuterio-1-acenaphthenylcarbinols.Similarly, treatment of the same aluminum reagent with O2 gives a 1:1 mixture of cis- and trans-2-deuterio-1-acenaphthenols.The magnetically shielded C8 or ortho proton in the original aluminum adduct offers a valuable monitor of the extent of complexation at the C1-Al bond.The present findings demonstrate that electrophilic attack at the ortho position (leading to C3 substitution) in the kinetically controlled process, while rearrangement to C1 is thermodynamically determined.