Radical Reactions. Newly Emerged Tools for the Synthesis of Cyclic Compounds

20 RADICAL REACTIONS. NEWLY EMERGED TOOLS FOR THE SYNTHESIS OF CYCLIC COMPOUNDS 

Despite these complications, the enormous and unique synthetic potential of radical reactions is also obvious. Radicals are highly reactive species and their addition to multiple bonds occurs easily, even with crowded substrates, under mild and essentially neutral conditions. Radical reactions are not generally sensitive to the influence of polar effects and tolerate the presence of functional groups otherwise incompatible with electrophilic and/or nucleophilic reagents. 

An intramolecular version of this reaction was especially efficient with ji-dicarbonyl derivatives such as 420- 22. In fact, the transformations of these substrates into the tricyclic lactones 423-425 occurred under mild conditions and gave the target compounds in good yields and with complete control over the regio- and stereochemistry of the ring junctions. It is also to be noted that the starting substrates were prepared by routine methods from readily available precursors. 

In this section, we have presented some of the main approaches for the construction of cyclic systems, not a complete coverage of all possible routes. Our intention was to highlight general trends in the solutions of various problems in this area and to emphasize the flexibility of the elaborated pathways specifically adjusted for diverse synthetic tasks. 

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