Synthesis of Benzofurans via Aryne-Iodonium Ylide Cycloaddition

Significance

o-Silyl aryltriflates, converted into benzynes in situ under mild conditions, undergo cycloaddition with iodonium ylides to yield benzofuran derivatives. A similar process was reported over 30 years ago by Caubere and co-workers from dihalobenzenes and cyclic ketone enolates (P. Caubere et al. J. Org. Chem. 1975, 40, 2853), but the conditions used were much harsher (NaNH₂ + NaOt-Bu). The reaction scope was well studied and the yields are generally fair to good, except when R² = sterically demanding groups, such as 2-IC₆H₄ (32% yield). A ca. 1:1 mixture of products arises when R¹ = 4-Me.