Dienes zirconocene-catalyzed reductive

Scheme 4 Mechanism of the zirconocene-catalyzed reductive cyclization of dienes...

With the advent of enantioselective zirconocene-catalyzed alkene carbomagnesiation,27 27a 27c 28 28a chirally modified zirconocenes soon were applied to asymmetric reductive diene carbocyclization.2 a c As demonstrated by the reductive cyclization of 5a,29 highly enantioselective cyclization is enabled through the use Brintzinger s chiral, mszz-zirconocene.30 30a (For the preparation and resolution of chiral tf .szz-zirconocene 6, see Refs 30,30a.) However, moderate diastereoselectivities and yields are generally observed (Scheme 5). 

The use of organomagnesium reagents as terminal reductants in zirconocene-catalyzed diene reductive cyclization permits derivatization of the resulting bis(magnesiomethyl)cycloalkanes. However, the use of other stoichiometric reductants is likely to afford catalytic systems that exhibit complementary selectivity profiles. Molander reports the... 

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