Tandem reactions polycyclic molecules

Tandem cyclisation-cycloaddition reaction of a-diazoacetopheno-nes yield polycyclic molecules in one single step. The synthetic interest of these reactions is further enhanced by the fact that the cycloadducts are easily rearranged to different products according to reaction conditions. 

From the selective sampling of cascade reactions for the synthesis of heterocyclic molecules that has been outlined in this chapter, it is clear that virtually any reaction can be incorporated into a tandem sequence. Some cascade sequences increase molecular complexity more than others, but each seems to provide complex heterocyclic structures in a more efficient manner than the corresponding chemistry wherein each intermediate is isolated. Indeed, many of these cascades rapidly construct hetero-polycyclic systems that are difficult to produce in other ways. 

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