New Aspects of the Fries Rearrangement

Reactions of 4-benzoyl-4-methylcyclohexa-2,5-dienone in acids: retro-Fries rearrangements

“…Any part of the rearrangement which is by an intramolecular, synchronous process is a [ 1,5] sigmatropic shift. A number of [1,5] shifts of acyl groups are particularly 6-2 shifts in cyclohexa-2,4-dienones.30-33 None, however, has been reported to be quite as fast as in our present work. Ester groups do not migrate as readily.32 Some relative rates, determined at 300°C for thermal [l,S] shifts of PhCO, MeCO and MeOCO were 380: 138: 1,28 and in four different compounds, in P h 2 0 as solvent, MeCO migrated as fast at 140 "C as MeOCO at 255 0C.29 Accordingly, acyl groups should also migrate more rapidly than alkoxycarbonyl in any part ofour retro-Friesreaction whichoccurs bya[1,5]sigmatropicpathway.…”

“…For this process we postulated an intramolecular reaction in which the dienone carbonyl group reacts with the amine to form an intermediate FTh 0-c=o 11, which then suffers an intramolecular trans-acylation with elimination of the amine molecule. Analogies were given for such [1,5]-shifts involving groups attached at the 1-and 4-positions of 6-membered rings2' In the present case, an intramolecular migration would presumably have to be formulated as shown in Scheme 1. All the indications are that the dienone would be protonated predominantly at the dienone carbonyl group.…”

Polycyclic Aromatic Ketones – A Crystallographic and Theoretical Study of Acetyl Anthracenes

“…2009;Titinchi et al, 2008;Adams et al, 1998;Okamoto & Yonezawa, 2009]. Notable cases are the report by Balaban [Frangopol et al, 1964;Balaban, 1966;Nenitzescu & Balaban, 1964] on the reversibility of Friedel-Crafts acetylation of olefins to -chloroketones, the report by Effenberger [Effenberger et al, 1973] of the retro-Fries rearrangement of phenyl benzoates (CF 3 SO 3 H, 170 °C) and the reversible ArS E aroylation of naphthalene derivatives [Okamoto & Yonezawa, 2009]. Additional examples are the acyl rearrangements of acetylphenanthrenes [Levy et al, 2007] and acetylanthracenes [Mala'bi et al, 2009] in PPA, the acetylation of fluorene [Titinchi et al, 2008], the disproportionation of 9-acetylanthracene into 1,5-and 1,8-diacetylanthracenes in an ionic liquid systems [Adams et al, 1998].…”

“…The Haworth synthesis of PAHs, which previously had allowed access to angularly annelated PAHs could thus be applied to the synthesis of linearly annelated PAHs [Agranat & Shih, 1974b]. Further experimental evidence in support of true reversibility of Friedel-Crafts acylation is limited [Frangopol et al, 1964;Balaban, 1966;Nenitzescu & Balaban, 1964;Effenberger et al, 1973;Levy et al, 2007;Mala'bi et al,. 2009;Titinchi et al, 2008;Adams et al, 1998;Okamoto & Yonezawa, 2009].…”

Reversible Friedel–Crafts acyl rearrangements of planar polycyclic aromatic ketones: dibenzofluorenones

“…13 Further experimental evidence in support of true reversibility of Friedel-Cras acylations and acyl rearrangements is limited. [14][15][16][17][18][19][20][21][22][23] The relative contribution of kinetic control versus thermodynamic control in Friedel-Cras acyl rearrangements remains an open question, in spite of the rich chemistry of Friedel-Cras acylations. 1,24 We have recently reported that kinetic control wins out over thermodynamic control in the Friedel-Cras acyl rearrangements of diacetylanthracenes in PPA.…”