Stereospecific cis-hydroalumination is possible through the use of dialkylalanes. The most common reagent used for this purpose is di(isobutyl)aluminium hydride (DIBAL-H). Analogous to hydroboration reactions with RBH, hydroalumination with RAlH leads to the attachment of aluminium at the carbon less able to stabilize developing positive charge (anti-Markovnikov selectivity). Metalation of terminal alkynes is a significant side reaction that occurs under these conditions. If metalation is desired, tertiary amine complexes of DIBAL-H are useful.
The use of silyl acetylenes avoids the problem of competitive metalation of terminal alkenes. The stereoselectivity of hydroalumination can be altered through a change in solvent: tertiary amine solvents provide the cis alkenylalane and hydrocarbon solvents provide the trans isomer.
Lithium aluminium hydride hydroaluminates alkynes to afford trans alkenylalanes. In equation (7) hydride adds to the terminal carbon, which places the developing negative charge next to the stabilizing phenyl substituent.