Benzynes double cyclization

Aryne cycloadditions have been coupled with radical cyclizations to rapidly assemble multiring systems For example, benzyne addition to furan 278 followed by radical cyclization onto the newly formed double bond gave 280 in two steps and fair yield. 

Cheng and co-workers reported the synthesis of isochromenones and oxepines via Pd-catalyzed eascade cyclization of allq nes and benzynes in 2012. The reactions involve biscarbocyelization of allq nes and benzynes and C-H bond activation. Phenanthro[l,10-Z)c]-oxepine derivatives were prepared in good to excellent yields (Scheme 4.26a). They also developed the synthesis of seven-membered lactones via nickel- and zinc-catalyzed cyclization of 2-iodobenzyl alcohols with allq l propiolates (Scheme 4.26b). The catal) ic reaction involves an unusual ElZ isomerization of a earbon-carbon double bond prior to ring elosure and provides a convenient and unique method for the synthesis of seven-membered lactones. 

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