Spiro Cyclohexadienones from the Reaction of Phenolic Enaminone Derivatives with Hypervalent Iodine Reagents

Abstract

Phenolic enamino compounds, prepared from 2-(4-hydroxyphenyl)-ethylamine and the corresponding -keto carbonyl compounds, afford spiro cyclohexadienone derivatives on reaction with hypervalent iodine reagents.

Recent Developments in the Chemistry of Polyvalent Iodine Compounds

“…Ortho -substituted phenols can be oxidized similarly with the formation of the respective 2,4-cyclohexadienone derivatives. Various nucleophiles, such as alcohols, fluoride ion, amides, allylsilane, and electron-rich aromatic rings, have been successfully used in this reaction (Scheme 6) in either an inter- or intramolecular mode. − Recent examples of the synthetic application of this reaction in the intermolecular mode include the preparation of dimethoxyketal 197 (eq 86), which is an essential precursor in the enantioselective synthesis of the potent antifungal agent (−)-jesterone, various dimethoxyketals of para - and ortho -benzoquinones, − the nucleophilic para -fluorination of binaphthol 198 (eq 87) 202 or 4-substituted phenols, and the preparation of 2,4-cyclohexadienone derivatives 202 (eq 88) 204 by the oxidation of 2-alkoxynaphthols in the presence of an allylsilane or a silyl enol ether as a carbon-based nucleophile.

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Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

“…Like PIDA and PIFA, Koser reagents are other iodine(III) reagents known to behave as electrophiles. In 2000, Spyroudis and co-workers [ 109 ] reported the spirocyclization of para -substituted phenols 102 to corresponding spirocarbocyclic derivatives 104 via dearomatization process using Koser reagent. In this reaction, substrates 102 were reacted with a stoichiometric amount of [(hydroxy)(tosyloxy)iodo]benzene ( 103 ) in dichloromethane at 0 °C.…”

Hypervalent Iodine Chemistry: 25 Years of Development at the University of Thessaloniki

“…59 Similarly, in a more predictable way, the enaminone 44 was converted by [hydroxy(tosyloxy)iodo]benzene to the spiro compound 45. 60 These reactions may proceed via the intermediacy of a phenyliodonio derivative from the starting enamine. However, the β-aminocrotonate derivative 42 is not attacked at C-2, as it happens with reactions of the previous section, but either at N or at C-3, which is rendered more electrophilic after N-trifluoroacetylation.…”