Hypervalent iodine oxidation of α-substituted 2,4-dihydroxyacetophenones: synthesis of novelo-iodophenoxy ethers via rearrangement of iodonium ylides

Abstract

α-Substituted 2,4-dihydroxyacetophenones (1a-1i) have been oxidized with phenyliodonium diacetate (PIDA) under three conditions (i) PIDA-KOH-MeOH (basic) at 0°C, (ii) PIDA-MeOH (neutral) at reflux temperature, and (iii) PIDA-AcOH (acidic) at reflux temperature, to afford novel o-iodophenoxy ethers (4a-4i) via rearrangement of respective iodonium ylides (5a-5i).

Zwitterionic Iodonium Compounds: Useful Tools in Organic Synthesis

“…This localization can be explained by the internal hydrogen bond between the hydroxy group at position 3 and the carbonyl of the acetyl group. The same kind of reactivity was observed later in analogous iodonium phenolates bearing various acyl groups in the place of the acetyl group 11. …”

Recent Developments in the Chemistry of Polyvalent Iodine Compounds

“…Several new, potentially important classes of iodonium ylides have been prepared and investigated in the last 5 years. [479][480][481][482][483][484][485][486][487] Spyroudis and Varvoglis reported the synthesis of a new class of stable zwitterionic aryliodonium compounds 589 from 2-amino-1,4-naphthoquinone 588 and [hydroxy(tosyloxy)iodo]arenes (eq 244). [479][480][481] Ylides 589 show an interesting reactivity: upon heating, aryl migration from iodine to nitrogen is observed (eq 245), while the photochemical reaction with aromatic compounds and furan leads to substitution products 591 (eq 246).…”

“…480 Prakash and co-workers reported the preparation of the stable zwitterionic aryliodonium compounds 593 by the reaction of 2,4-dihydroxyacetophenones 592 with (diacetoxyiodo)benzene (eq 247). 482 Heating of these compounds leads to aryl migration from iodine to oxygen with the formation of the appropriate o-iodophenoxy ethers.…”

Synthesis of 3‐Aryloxy‐2‐iodoemodines by Oxidation of Emodin with (Diacetoxyiodo)arenes

“…[19] A mechanistic pathway similar to the oxidation of 2,4-dihydroxyacetophenones with DIB for the reaction of emodin (1) to 4aϪf with various (diacetoxyiodo)arenes 2aϪf is outlined in Scheme 2. We assume that (diacetoxyiodo)arenes [ArI(OAc) 2 ] are converted into (dimethoxyiodo)arenes [ArI(OMe) 2 ] under highly alkaline conditions (KOH in MeOH), [20] while emodin changes into the corresponding emodinate I in situ. (Dimethoxyiodo)-arenes attack emodin at position 2 to form intermediates II followed by formation of the iodonium ylides 3aϪf.…”