Addition reactions continued enones

A study of the intramolecular (2+2)-addition in the enones (77) has been reported. The outcome of the addition is both temperature and substituent dependent. Thus irradiation of the enone (77a) at 0°C in acetonitrile with benzophenone as the sensitizer yields a single adduct (78) in 90% yield after only 35 min. irradiation. The photocycloaddition of the enone (77b) at lower temperatures yields a mixture of (78) and (79) in a ratio of 1.8 1. The other derivatives (77c,d) afford only one product identified as (79). The products obtained from the cycioaddition can be cleaved to spiroacetals. The synthetic potential of the intramolecular (2+2)-cycloaddition reaction of enones continues to be exploited. In a recent example example the cycioaddition of the enone (80) affords the product (81) which is then subjected to ring-opening and further transformation to provide a path to the natural product (+)-ligudentatol (82). " ... 

In total, over the past six years, the chelating P,N-ligands have shown considerable promise in a variety of enantioselective processes, including transfer-hydrogenation and hydrosilylation of ketones, hydroboration of alkenes, conjugate addition to enones and Lewis-acid catalysed Diels-Alder reactions, in addition to those described above.128,341 It is anticipated that this list will continue to grow, and... 

The chiral molecular receptor (35) has been used to effect enantioselective cyclization of the enone (36). The complex of (36) and (35) undergoes energy transfer from the ketonic acceptor to (36) and results in its conversion into the cyclobutanes (37) and (38) in a total yield of 21%. Bach et aV have continued their investigations of enantioselective additions mediated by the chiral lactam hosts (39). The present reactions involve intra and intermolecular additions of quinolone systems (40) at -60°C in toluene as solvent. The irradiation affords the cycloadducts (41) and (42). As can be seen, the ee of the products is high and the chemical yields are also good. An extension of the work to intermolecular reactions of the quinolone (43) was also reported. The additions of the alkenes... 

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