Hydrindanone, formation

Scheme 9. Enantioselective domino reaction for the formation of hydrindanones with heterobimetallic catalysts...

The cycloadditions of (Ti -allyl)Fp complexes to alkenes proceed with high chemoselectivity. Only highly activated alkenes such as methylenemalonates, benzylidenemalononitrile, TCNE or I,2-di-cyano-4,5-dichloroquinone will participate in the reaction. With the less electrophilic a,p-unsaturated systems, cycloaddition can only be effected with Lewis acid activation. Thus the cycloadduct (6) is formed in reasonable yield (as a mixture of stereoisomers) from (3) and cyclohexenone using freshly sublimed AlBn (equation 4). The same reaction gives only a 8% yield with Aids. The exclusive formation of a ci.r-hydrindanone system can be explained by suprafacial attack of the enone on the allyl unit, which is then followed by another suprafacial ring closure of the dipolar intermediate, affording the thermodynamically preferi cyclic system (7a) and (7b). ... 

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