Chiral proton H -Induced Polyene Cyclizations

Well-designed chiral Brpnsted acid (HL ) were found to adequately discriminate the enantioface of the terminal isoprenyl group of linear polyprenoids, leading to high enantioselective protocyclizations when concerted reactions were occurred. On the other hand, when stepwise pathway is thermodynamically preferred, the enantioselectivity is amenable to lower ee s (Schane 9.11). 

SCHEME 9.11 Enantioselective protocyclization of a linear polyprenoid with chiral Br0nsted acid. 

SCHEME 9.13 Enantioselective polyene cyclization promoted by LBA 7-SnCl.  

This method provides the first route to enantioenriched ferruginol (R = (-Pr), since ( )-6 (R = H) has already been converted into racanic ferruginol by King s [19] and Ghatak s group [20]. 

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