Asymmetric alkene cycloalumination by AlEt3, catalyzed with neomenthylindenyl zirconium η5-complexes

The paper is devoted to a study of the reaction of terminal alkene cycloalumination by AlEt3 catalyzed with neomenthylindenyl zirconium complexes (p-S)(p-S)-bis[η5-[1-[(1S,2S,5R)-2-isopropyl-5-methylcycloh-exyl]indenyl]]zirconium dichloride (1) or (p-S)-(η5-cyclopentadienyl)[η5-[1-[(1S,2S,5R)-2-isopropyl-5-methylcyclohexyl]indenyl]]zirconium dichloride (2). It was shown that alkene and catalyst structures, as well as solvent, affect the overall yield and enantiomeric excess of the reaction product - 3-alkylsubstituted aluminacyclopentanes. The reaction of terminal alkenes with AlEt3, catalyzed by complex 1, in hydrocarbon solvents gives predominantly S-enantiomers of cyclic organoaluminum compounds with enantiomeric excess up to 37%. Complex 2 shows smaller stereoinduction effect and provides R-enantiomers of aluminacyclopentanes with 6–26%ee.The effectiveness of selenium-containing derivatizing reagent (R)-2-phenylselenopropanoic acid for the enantiomeric excess estimation in β-alkyl-1,4-butanediols obtained from cyclic organoaluminum compounds was shown.

Graphical abstractThe reaction of terminal alkene cycloalumination by AlEt3 catalyzed with neomenthylindenyl zirconium η5-complexes of C1 and C2-symmetry has been studied. The enantioselectivity of the reaction was estimated by the analysis of oxidation and hydrolysis products – β-alkyl-1,4-butanediols, which were derivatized by MTPA and (R)-2-phenylselenopropanoic acid.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Alkene cycloalumination by AlEt3, catalyzed with (NMI)2ZrCl2, provides aluminacyclopentanes with ee ≤ 37%, S. ► Catalysis by complex Cp(NMI)ZrCl2 gives aluminacyclopentanes with ee ≤ 26%, R. ► The effectiveness of (R)-2-phenylselenopropanoic acid for the enantiomeric excess estimation in β-alkyl-1,4-butanediols is shown.