The Coming of Age in Iodane-Guided ortho-C-H Propargylation: From Insight to Synthetic Potential.

As early as 1991 Ochiai et al. reported that an acid-activated form of phenyliodine diacetate, PhI(OAc)2 , undergoes a reaction with propargyl-silanes, germanes and stannanes to give the ortho-propargyl iodobenzene. This formal C-H alkylation was proposed to take place through an unusual (even to date) iodonio-based [3,3] rearrangement of an intermediate allenylsilane. Although this mechanistic principle has been invoked in related iodane-directed C-H coupling reaction, some underlying principles have remained unaddressed, and the reaction rarely employed. Herein, DFT evidence for a mechanism best described as iodine-guided electrophilic aromatic substitution is presented. Using a newly optimized reaction protocol that significantly reduces the undesired reduction process, the potency of the method is showcased through the synthesis of >40 structurally diverse ortho-iodo propargyl (or allenyl) arenes.