Unprecedented regiochemical control in the formation of aryl[1,2-a]imidazopyridines from alkynyliodonium salts: mechanistic insights

Luke I. Dixon, Michael A. Carroll, Thomas J. Gregson, George J. Ellames, Ross W. Harrington, William Clegg
2013 Organic and biomolecular chemistry  
Aryl(alkynyl)iodonium salts have been demonstrated to be valuable precursors to a diverse range of heteroaromatic ring systems including aryl[1,2-a]imidazopyridines. Successful application, using the recently described aryl(alkynyl)iodonium trifluoroacetate salts, is described, highlighting for the first time that the regioselectivity of this process is both counter-ion and concentration dependent. Studies with a carbon-13 labelled substrate established that the reactions of alkynyliodonium
more » ... alkynyliodonium salts are highly complex and that multiple mechanistic processes appear to be underway simultaneously. Scheme 1 Heteroaromatics from alkynyliodonium salts. 2,4 † Electronic supplementary information (ESI) available: Full experimental details and spectra, tables of X-ray crystallographic data and results. CCDC 907271-907274. For ESI and crystallographic data in CIF or other electronic format see Scheme 3 Distribution of products from the reaction of [7'-13 C]-1. Scheme 4 Mechanism of isotopomer formation; [3-13 C]-3a. § Although several column packings were evaluated, e.g. reverse phase silica, alumina (neutral, basic and acidic), with a range of solvents and additives, the Grace cartridges were found to provide satisfactory purification.
doi:10.1039/c3ob41112e pmid:23903567 fatcat:3nxix5r575hd7cparxoj6kmudy