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Cyclometalation of allylbenzene by EtAlCl2 and Mg in the presence of Zr ansa-complexes as synthetic route to dibenzylbutane and 9,8′-neo- lignans
* 1 , 1 , 2 , 2 , 1
1  Institute of Petrochemistry and Catalysis of Russian Academy of Sciences
2  A. V. Topchiev Institute of Petrochemical Synthesis RAS
Academic Editor: György Keglevich

Abstract:

The aim of the research is the development of an one-pot method for the synthesis of biologically active compounds – lignans. For this purpose the ansa-zirconocenes of various structures were tested as the catalysts of the allylbenzene cyclometalation with ethylaluminum dichloride (EtAlCl2) and Mg. The effect of organophosphorus compounds hexamethylphosphoramide (HMPA) and triphenylphosphine (PPh3) on the chemo- and regioselectivity of the reaction was studied. It was shown that the structure of the η5-ligand at the Zr atom significantly affects the activity of the system, and the presence of HMPA increases the yield of cyclometalation products up to 77%. The reaction proceeds with the formation of regioisomers of 3,4-dibenzyl- and 2,4-dibenzyl-substituted alumolanes with a ratio (1-2):1, which hydrolysis provides corresponding dibenzylbutane and 9,8'-neo- lignans.

Keywords: cyclometalation, alkenes, zirconocenes, lignan
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