Iodination of antipyrine with [N–I–N]⁺ and carbonyl hypoiodite iodine(i) complexes

Abstract

A series of iodine(I) complexes, both known and new, were synthesised and the dependence of iodination reactivity on the identity of the Lewis bases and anions present was investigated. Using...

Chiral carbonyl hypoiodites

“…15 However, these studies were performed with an unrestrained homoleptic iodine(I) complex (BR), with the chiral iodine(I) complexes only being studied only as their restrained, bidentate complexes, 16 which is also hindered by their availability (or lack thereof). 17 Whilst heteroleptic iodine(I) complexes have been confirmed in the solid state, 18 the observation of them undergoing ligand scrambling in solution has stifled potential studies into their use. 18,19 These results negate synthetic strategies toward creating heteroleptic iodine(I) complexes via the use of chiral ligands, given that the unwanted recovery of meso isomers is highly probable.…”

“…The recent revitalisation of carbonyl hypoiodites, 17,[21][22][23] as seen from the viewpoint of halogen bonding as isolable iodine(I) complexes, offers an alternative to the traditional [N-I-N] + complexes like BR. The carbonyl hypoiodites are inherently heteroleptic, but can still be synthesised in an analogous fashion via a similar Ag + to I + cation exchange as the [N-I-N] + complexes.…”

“…24 These hypoiodites have been reported to perform a variety of exotic transformations, 25,26 as well as recently being confirmed to perform the same straightforward iodinations that BR can. 17 Discerning structure-reactivity relationships can be difficult though, as such hypoiodite reagents like CH 3 C(O)OI and t BuOI have only limited solution-state data available in the literature, 27,28 with the identities of the actual reactive species being unresolved. 29,30 Herein, the first examples of chiral carbonyl hypoiodite complexes from N-protected (S)-valine are reported.…”

“…15 However, these studies were performed with an unrestrained homoleptic iodine( i ) complex ( BR ), with the chiral iodine( i ) complexes only being studied only as their restrained, bidentate complexes, 16 which is also hindered by their availability (or lack thereof). 17…”

“…The reaction of 2 in dichloromethane with elemental iodine and a pyridine-based ligand, either 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (4-pyrpy), or 4-morpholinopyridine (4-morpy), gave the carbonyl hypoiodites DMAP ( S )- N -phthaloylvalinoyl hypoiodite ( 3a ), 4-pyrpy ( S )- N -phthaloylvalinoyl hypoiodite ( 3b ), 4-morpy ( S )- N -phthaloylvalinoyl hypoiodite ( 3c ) (Scheme 1). All the hypoiodite complexes ( 3a–3c ) could be isolated as pure solids in 65% to 91% yields, ideal for prospective reagents, 17 which can be a weakness of highly reactive iodine( i ) complexes. 8,32 The synthesis of the analogous derivative with pyridine, ( S )- N -phthaloylvalinoyl hypoiodite(pyridine), was attempted given that it would be the directly comparable to BR .…”