Radical formation and cyclization

Following the exploration of the synthetic utility of aren-ediazonium salts in radical formation and cyclization— radical-polar crossover [1-6]—Murphy described a new indole synthesis based on his methodology (Scheme 1, equations 1 ) [7-9], The requisite precursor diazonium salts can be rapidly assembled from o-nitroani-line. In cases where the fully aromatic indole ring is not... 

A synthetic method for the introduction of an ethynyl group in cyclic structures is based on an intramolecular silicon-tethered radical cyclization with iodine transfer (Scheme 25.8). For example, starting from alkyne 10, a triethyl borane-initiated process allows a radical formation and cyclization to give the alkenyl radical 11. An iodine atom is abstracted from the starting material to give the alkenyl iodide 12, thus, propagating the chain. Treatment of 12 with tetra-/j-butylammonium fluoride (TBAF) results in elimination to furnish 13 in good yields. 

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