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Please login or sign up for a free trial to access the full content. Variation 2: Hydroalumination of Alkenes and Alkynes

DOI: 10.1055/sos-SD-007-00207

Oishi, M.Science of Synthesis, (20047287.

Alkene and alkyne hydroalumination is a thermodynamically favored, useful transformation in organic synthesis. The chemistry has been well surveyed in several articles.[‌23‌,‌24‌,‌27‌] Three types of aluminum reagents, namely lithium aluminum hydride, dialkylaluminum hydride, and trialkylaluminum compounds with β-hydrogens, are typically used for hydroalumination with CC unsaturation. Alkene hydroalumination occurs at elevated temperatures without a catalyst.[‌12‌,‌28‌,‌30‌] However, early and late transition-metal catalysts can be employed to accelerate the reaction.[‌228‌] The hydroalumination of alkynes with tri­isobutylaluminum and diisobutylaluminum hydride occurs without any catalyst; however, it is difficult to avoid side reactions and the undesired subsequent reaction of the remaining alkyne substrates. Thus, this section overviews metal-catalyzed hydroalumination of alkenes and alkynes with trialkylaluminum compounds. Representative reagents for alkene hydroalumination are triisobutylaluminum and triethylaluminum. As illustrated in Scheme 51, these trialkylaluminum reagents are generally transmetalated or the AlC bond is inserted by transition metals. β-Hydrogen elimination generates the transition metal hydride species for hydrometalation and final alkyl transfer to aluminum or reductive elimination completes the catalytic cycle.

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