Radical-and Nucleophilic Cyclization

As the bulk of the cyclizations reported started with an electrophilic attack at the double bond, we want to finish this section with at least one further radical induced and one nucleophilic cydization. In radical cyclizations the halomethyl-dimethylsilyl group has become quite popular as radical starter and generally one makes use of H2O2 oxidations to finally cleave the carbon-silicon bond [169]. 

As the following reaction schemes indicate, the stereoselectivity of the reported hydrindane synthesis can be controlled by the choice of the starting materials. 

In the cis-hydrindane synthesis it is the hydrogen radical that approaches from the convex side of the bicychc silylether intermediate 454 (see 454 ), thus generating the cis-ring juncture of457. 

To arrive at the trans-hydrindane 459 the aUyl radical is introduced this way and consequently estabHshes the trans orientation of the hydrogen atoms at Cj and Cj. 

In this sequence, only one single diastereomer is formed albeit only in 20% overall yield [170], 

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