Kinetic control wins out over thermodynamic control in Friedel-Crafts acyl rearrangements

Article abstract of DOI:10.1016/j.tetlet.2011.02.026

1,5-, 1,8- and 9,10-diacetylanthracenes undergo Friedel-Crafts acyl rearrangements in polyphosphoric acid at 130-150 °C to give 3-methylbenz[de]anthracen-1-one via the kinetically-controlled 1,9-diacetylanthracene. The rearrangement mechanism is supported by DFT calculations of diacetylanthracenes, their σ-complexes, O-protonates, and O,O-diprotonates. The importance of kinetic control versus thermodynamic control in Friedel-Crafts acyl rearrangements is highlighted. Certain features of reversibility are also suggested.

Full text of DOI:10.1016/j.tetlet.2011.02.026

Tetrahedron Letters 52 (2011) 1854–1857
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Kinetic control wins out over thermodynamic control in Friedel–Crafts
acyl rearrangements
⇑
Tahani Mala’bi, Sergey Pogodin, Israel Agranat
Organic Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Philadelphia Bldg, #201/205, Edmond J. Safra Campus, Jerusalem 91904, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
1,5-, 1,8- and 9,10-diacetylanthracenes undergo Friedel–Crafts acyl rearrangements in polyphosphoric
acid at 130–150 °C to give 3-methylbenz[de]anthracen-1-one via the kinetically-controlled 1,9-diacetyl-
anthracene. The rearrangement mechanism is supported by DFT calculations of diacetylanthracenes,
Received 28 December 2010
Revised 20 January 2011
Accepted 4 February 2011
Available online 4 March 2011
their
r-complexes, O-protonates, and O,O-diprotonates. The importance of kinetic control versus thermo-
dynamic control in Friedel–Crafts acyl rearrangements is highlighted. Certain features of reversibility are
also suggested.
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Diacetylanthracenes
Polyphosphoric acid
Reversibility
Rearrangement mechanism
DFT calculations
Friedel–Crafts acylation, in contrast to Friedel–Crafts alkylation,
is usually considered an irreversible process, free of rearrangements
and isomerizations.1–3 However, if the acyl group is tilted out of
the plane of the aromatic ring by the neighboring bulky group(s),
the resonance stabilization is reduced and the pattern of irrevers-
ibility of the Friedel–Crafts acylation may be challenged, allowing
deacylations, transacylations, and acyl rearrangements.4–6 The con-
cept of reversibility in Friedel–Crafts acylation was put forward in
1955 by Gore, who proposed that ‘the Friedel–Crafts acylation reac-
tions of reactive hydrocarbons is a reversible process’.7,8 The incur-
sion of reversibility in the Friedel–Crafts acylation was revealed in
the benzoylation of naphthalene in polyphosphoric acid (PPA) at
elevated temperatures.9 Under classical Friedel–Crafts acylation
conditions (e.g., AlCl3 and a trace of H2O), the pattern of irreversibil-
ity (e.g., in the naphthalene series) has been highlighted.6,8,10,11 The
existing experimental evidence in support of the true reversibility of
Friedel–Crafts acylation is limited.12–17 Notable cases are the report
by Balaban on the reversibility of Friedel–Crafts acetylation of
olefins to b-chloroketones,12–14 the report by Effenberger of the ret-
ro-Fries rearrangement of phenyl benzoates (CF3SO3H, 170 °C)15
and the reversible ArSE aroylation of naphthalene derivatives.17
Complete reversibility of Friedel–Crafts acylation was established
in the intramolecular para ꢀ ortho acyl rearrangements of fluoroflu-
orenones in PPA.18 Friedel–Crafts acylation can be adjusted to give a
kinetically controlled ketone or a thermodynamically controlled
ketone.4 Acyl rearrangements and reversibility in Friedel–Crafts
acylations have been associated with thermodynamic control.5,9,18
The contributions of kinetic control versus thermodynamic control
in Friedel–Crafts acyl rearrangements remain an open question, in
spite of the rich chemistry of the Friedel–Crafts acylation.
Aspects of reversibility and acyl rearrangements of mono-
acetylanthracenes and mono-acetylphenanthrenes in PPA have
been reported, but complete reversibility has not been real-
ized.19,20 The complexity of the Friedel–Crafts acetylation of
anthracene is enhanced by diacetylation. Indeed, the disproportio-
nations of 9-acetylanthracene into 1,5-diacetylanthracene and
1,8-diacetylanthracene in an ionic liquid system have been de-
scribed.16 The study of the mutual Friedel–Crafts acyl rearrange-
ments of diacetylanthracenes with special emphasis on kinetic
versus thermodynamic control seemed an attractive proposition.
We provide here experimental and theoretical evidence indicating
the importance of kinetic control in the Friedel–Crafts acyl
rearrangements in the diacetylanthracene series. We report that
surprisingly, the Friedel–Crafts acyl rearrangements of 1,5-diace-
tylanthracene (1,5-Ac2AN), 1,8-diacetylanthracene (1,8-Ac2AN)
and 9,10-diacetylanthracene (9,10-Ac2AN) in PPA gave 3-methyl-
benz[de]anthracen-1-one (1) via the putative kinetically controlled
intermediate, 1,9-diacetylanthracene (1,9-Ac2AN).
1,5-Ac2AN,21,22 1,8-Ac2AN23 and 9,10-Ac2AN24 were each sub-
jected to PPA at 130–150 °C for 1–4 h. The results are summarized
in Table 1. The constitution of the crude products was established
by 1H NMR spectroscopy. The constitutional isomers 1,5-Ac2AN,
⇑
Corresponding author.
E-mail address: isria@vms.huji.ac.il (I. Agranat).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.02.026

T. Mala’bi et al. / Tetrahedron Letters 52 (2011) 1854–1857
1855
Table 1
CH3
O
CH3 H3C
O
O
The products of the rearrangements of diacetylanthracenes
Substrate
m,n-
T
t
Products (% relative yield)
m-AcAN
m,n-Ac2AN
H3C
Ac2AN
(°C)
(h)
1
2
9
1,5
1,8
9,10
1
AN
(1Z,6Z)-Ac2AN
2
3
O
1,5
1,5
1,5
1,8
1,8
1,8
1,8
9,10
9,10
140
150
150
130
130
140
150
150
150
1
1
3
3
4
1
3
1
3
0
0
0
0
0
0
0
3
0
26
30
0
11
0
17
9
8
0
0
0
0
0
0
0
0
0
14
15
5
0
0
0
0
0
0
16
5
2
24
20
21
12
0
0
0
0
0
0
0
0
50
18
44
50
93
65
80
62
79
8
0
0
0
0
0
0
0
31
77
A plausible mechanism for the rearrangements of 1,5-Ac2AN
and 1,8-Ac2AN into 1 is presented in Scheme 1. The pivotal step
in this mechanism is the formation of 1,9-Ac2AN as an intermedi-
ate. 1,5-Ac2AN and 1,8-Ac2AN each undergoes deacetylation to
give 1-AcAN, followed by reacetylation to give the kinetically con-
trolled 1,9-Ac2AN (vide infra). The latter can also be formed by a
5
0
0
direct acyl rearrangement of 1,8-Ac2AN: 1,8-Ac2AN ? 1,8
Ac2ANH+1 ? 1,9 -Ac2ANH+1 ? 1,9-Ac2AN.
The rearrangement of the latter into
(1Z,9Z) ? (1Z,9E) diastereomerization.26 Figure 1 depicts the DFT-
calculated transition state for the rearrangement of 1,8 -Ac2AN
into 1,9
-Ac2AN (energy barrier DDGà298 = 35.9 kJ/mol, at B3LYP/
6-31G(d)). The 1,9-Ac2AN intermediate then undergoes an acid-
catalyzed irreversible intramolecular aldol condensation to give
1. 1,9-Ac2AN may also be an intermediate in the rearrangement
of 9,10-Ac2AN into 1 (see Scheme SD1, Supplementary data). The
acyl rearrangement mechanism also suggests certain features of
reversibility: 1,5-Ac2AN ? 1-AcAN ꢀ 1,8-Ac2AN. The reported
r-
r
1,8-Ac2AN, and 9,10-Ac2AN, the constitutional isomers 1-acetylan-
thracene (1-AcAN), 2-acetylanthracene (2-AcAN), and 9-acetylan-
thracene (9-AcAN) and anthracene (AN) were distinguished by
the 1H NMR chemical shifts of the methyl groups, by the low-field
chemical shifts of H9 and H10 (singlets) and the chemical shifts of
the protons ortho to the carbonyl group(s) (H1 and/or H2) (Table 2).
The major rearrangement product of the reactions of 1,5-Ac2AN
and 1,8-Ac2AN in PPA was 1. In both cases, 2-Ac2AN was also
formed. 1,5-Ac2AN also rearranged into 1,8-Ac2AN (probably via
1-AcAN), while 1,8-Ac2AN did not rearrange into 1,5-Ac2AN. Inter-
estingly, 1 was also formed from 9,10-Ac2AN. The latter also
underwent a rearrangement into 2-AcAN and deacetylation to give
AN as the major product. 1,6-Diacetylanthracene25 was not identi-
fied among the products of the reactions.
1
requires
a
r
r
formation of
1
from anthracene and diketene (HF, À30 to
+60 °C)27 may be rationalized by an initial Friedel–Crafts acylation
at C9, followed by an intramolecular alkylation at C1 and
dehydration.
Preparative rearrangement of 1,5-Ac2AN in PPA (at 150 °C) for
three hours gave 1 in 25% yield. The structure of 1 was verified
by 2D 1H NMR and 13C NMR spectroscopy. The very low field dou-
ble doublet of the bay-region H11 at 10.16 ppm (see Table 2) due to
the diamagnetic anisotropy effect of the neighboring C1@O is strik-
ing. The chemical shifts of the ethylenic H2 and of the CH3 group at
6.75 and 2.57 ppm, respectively, are also noteworthy. Compound 1
could be distinguished from its constitutional isomer, 1-methyl-
benz[de]anthracen-3-one (2) by the NOE between the CH3 and
H4 (8.01 ppm, dd) in 1, while no NOE was observed between CH3
and H11 (which would be expected for 2). The structure of the
highly strained 4-methylcycloocta[defg]anthracen-1-one (3) was
ruled out by the absence of a singlet due to H10. (Also, H11 of 3
which is not located in a bay region would not have been expected
to be so highly deshielded as H11 of 1). The DFT calculations also
The proposed mechanism is supported by the results of DFT
calculations of the diacetylanthracenes, their O-protonates, their
O,O-diprotonates and their
r-complexes at B3LYP/6-31G(d)
(Tables SD1–SD4, Supplementary data). Recently, a computational
model for predicting the site for electrophilic aromatic substitution
was reported.28 The model was based on DFT calculations of the
relative stabilities of the
r-complex intermediates and was applied
(inter alia) to Lewis acid protonated Friedel–Crafts acylations. Our
calculations (see Supplementary data for the details) give the fol-
lowing orders of relative free energies (DG298, kJ/mol) of 1,5-
Ac2AN, 1,8-Ac2AN, 1,9-Ac2AN, 1,10-Ac2AN, and 9,10-Ac2AN in each
series:
ꢀ
r
-complexes of diacetylanthracenes:
Ac2ANH+1), 5.68 (1,10
37.54 (1
,5-Ac2ANH+1), 38.26 (1
Ac2ANH+1), 66.99 (1 ,10-Ac2ANH+1).
DG298 = 0.0 (1,9r-
r
-Ac2ANH+1), 22.29 (9
r
,10-Ac2ANH+1),
show that 1 is more stable than 2 and 3:
(2), 346.39 (3) kJ/mol.
DG298 = 0.0 (1), 31.35
r
r
,8-Ac2ANH+1), 58.29 (1
r,9-
r
ꢀ O-protonated diacetylanthracene monocations:
D
G298 = 0.0
[(1Z,8Z)-1H-Ac2ANH+1], 1.79 [(1Z,5Z)-1H-Ac2ANH+1], 30.01
[(1Z,10E)-10H-Ac2ANH+1],
32.34
[(1Z,10Z)-1H-Ac2ANH+1],
Table 2
1H NMR chemical shifts (500 MHz, CDCl3, ppm) of characteristic protons in mono-
51.50 [(1E,9E)-9H-Ac2ANH+1],29 53.54 [(1E,9E)-1H-Ac2ANH+1],
and diacetylanthracenes, and in 1a
55.31 [(9E,10E)-9H-Ac2ANH+1].
CH3
H9
H10
H1
H2
ꢀ O,O-protonated diacetylanthracene dications:
D
G298 = 0.0
[(1Z,5Z)-Ac2ANH2+2],
11.24
[(1Z,8Z)-Ac2ANH2+2],
71.39
1-AcAN
2-AcAN
9-AcAN
1,5-Ac2AN
1,8-Ac2AN
2.81, s 9.48, s
2.76, s 8.57, s
2.82, s
2.82 s
8.44, s
8.43, s
8.47, s
9.57, s
—
8.65, s
7.86, d (8.5)
—
—
8.01, d (7.0)
—
7.47–7.55, m
8.08, d (7.0, 1.0)
8.14, d (8.5)
[(1Z,10Z)-Ac2ANH2+2], 88.44 [(1Z,9Z)-Ac2ANH2+2], 151.52
[(9E,10E)-Ac2ANH2+2].
—
9.57, s
ꢀ diacetylanthracenes:
D
G298 = 0.0 [(1Z,5Z)-Ac2AN],
11.20
2.83, s 10.17, s 8.47, s
[(1Z,8Z)-Ac2AN], 22.74 [(1Z,10Z)-Ac2AN], 42.63 [(1Z,9Z)-
Ac2AN], 43.87 [(9E,10E)-Ac2AN].
9,10-Ac2AN 2.81, s
—
—
8.52, s
7.84–7.88, m 7.53–7.57, m
1,6-Ac2AN
1
2.79, s 9.46 s
2.73, s
2.57, d
(1.0)
8.57,b
s
8.04, d (7.0)
—
8.73,c
s
10.16,d dd,
(9.0, 1.0)
8.01,e dd,
(7.3, 1.0)
Figure 2 depicts the relative energies of the most stable confor-
mations of each of the diacetylanthracene species. The B3LYP/6-
a
b
c
Coupling constants (J, Hz) are given in parentheses.
31G(d) calculated order of stabilities of the
diacetylanthracenes is 1,9
-Ac2ANH+1 > 1,10
10-Ac2ANH+1 > 1 ,5-Ac2ANH+1 > 1 ,8-Ac2ANH+1 > 1
,10-Ac2ANH+1. According to the Hammond-Leffler postulate,30 the
r
-complexes of
-Ac2ANH+1 > 9
,9-Ac2ANH+1
H5.
H7.
r
r
r,
>
H11
H4.
.
d
e
r
r
r
1r

1856
T. Mala’bi et al. / Tetrahedron Letters 52 (2011) 1854–1857
O
O
CH3
H3C
O
O
CH3
O
CH3
H3C
H
8
9
1
2
3
7
6
5
10
4
H3C
O
1σ,8–Ac2ANH +
(1
Z
,5Z
)–Ac2AN
(1
Z
,8
Z
)–Ac 2AN
O O
H3C
O
O
O
CH3
CH3
CH3
H3C
H
1,9σσ–Ac2ANH+
(1
Z
,9
Z
)–Ac2AN
(1Z )–AcAN
CH3 O
2
O
CH3
1
3
O
CH3
11
8
4
5
10
9
6
7
(1
Z ,9E)–Ac2AN
1
Scheme 1. The mechanism of Friedel–Crafts rearrangement of 1,5-Ac2AN and 1,8-Ac2AN leading to 1.
Figure 1. The transition state for 1,8r-Ac2AN ? 1,9r-Ac2AN rearrangement.
relative energies of the transition states leading to the
resemblethoseofthe -complexes:
Gà298 (1,9 -Ac2ANH+1) <
(1,10 (1 (1
-Ac2ANH+1) < Gà ,5-Ac2ANH+1) < Gà
ANH+1) < Gà ,9-Ac2ANH+1) < Gà ,10-Ac2ANH+1). Thus,
(1 (1
r
-complexes
r
D
r
D
Gà
298
r
D
r
D
r,8-Ac2
298
298
D
r
D
r
298
298
the DFT calculations predict that 1,9-Ac2AN is the kinetically con-
trolled product. Among the diacetylanthracenes, only 1,9-Ac2AN can
undergo an irreversible intramolecular aldol condensation to give 1.
By contrast, the calculations show that among the relevant diacety-
lanthracenes 1,5-Ac2AN, 1,8-Ac2AN, 1,9-Ac2AN, 1,10-Ac2AN, and
9,10-Ac2AN, 1,5-Ac2AN is the most stable. Among O-protonated
diacetylanthracenes, 1,5-Ac2ANH+1 and 1,8-Ac2ANH+1 are the most
stable. Thus they could have qualified as the thermodynamically con-
trolled diacetylanthracenes. The results indicate that the kinetically
controlled 1,9-Ac2AN eventually cyclizes irreversibly to 1. The
Friedel–Crafts acetylation of anthracene under classical conditions
Figure 2. Relative energies (
plexes (S), O-protonated diacetylanthracenes (P), diacetylanthracenes(K), and O,O-
diprotonated diacetylanthracenes (D).
D
G298) of m,n-diacetylanthracene species: r-com-
(AN, AcCl/AlCl3, CH2Cl2) yielded 1,5-Ac2AN (30–35 °C, 2 h) and 1,8-
Ac2AN (23 °C, 14 h), but not 1. Evidently, the r-complex of 1,9-Ac2AN,
the precursor of 1, could not have been formed due to a steric hin-
drance during complexation with AlCl3.

T. Mala’bi et al. / Tetrahedron Letters 52 (2011) 1854–1857
1857
In conclusion, the formation of 1 via 1,9-Ac2AN in the Friedel–
References and notes
Crafts acyl rearrangements of diacetylanthracenes in PPA (vide
supra) supports the contention that in these reactions, kinetic con-
trol wins out over thermodynamic control. It remains to be seen
whether this conclusion applies to other polycyclic aromatic ke-
tones (PAKs) and whether intermolecularity and/or intramolecu-
larity are essential ingredients of kinetic control in Friedel–Crafts
acyl rearrangements of PAKs (Agranat–Gore rearrangement19).
1. Friedel–Crafts Chemistry; Olah, G. A., Ed.; Wiley-Interscience: New York, 1973. p
102.
2. Comprehensive Organic Name Reactions and Reagents; Wang, Z., Ed.Friedel-Crafts
Acylation; Wiley, 2009; Vol. 1, pp 1126–1130. Chapter 248.
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Elsevier: London, 1965. pp 174–182.
4. Buehler, C. A.; Pearson, D. E. Survey of Organic Synthesis; Wiley-Interscience:
New York, 1970. p. 653.
5. Pearson, D. E.; Buehler, C. A. Synthesis 1971, 455–477.
6. Gore, P. H. Chem. Ind. 1974, 18, 727–731.
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Interscience: New York, 1964; Vol. 3, pp 1–381 (part 1).
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13. Balaban, A.T. In Omagiu Acad. Prof. Raluca Ripan,; Dragulesea, C., Ed.; Editura
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14. Nenitzescu, C. D.; Balaban, A. T. In Friedel–Crafts and Related Reactions; Olah, G.
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15. Effenberger, F.; Klenk, H.; Reiter, P. L. Angew. Chem., Int. Ed. Engl. 1973, 12, 775–
776.
In a 150 mL round-bottomed flask with a magnetic stirrer and
anhydrous argon atmosphere, PPA (133 g) was added; after stirring
for a few minutes at 150 °C, 1,5-Ac2AN (1.0 g, 3.8 mmol) was
added. The mixture was stirred at 150 °C for 3 h, and then poured
into a mixture of ice and water (500 mL) and stirred overnight. The
products were extracted with CH2Cl2 (4 Â 50 mL), washed with
saturated NaHCO3 solution (2 Â 50 mL) and H2O (2 Â 50 mL), and
dried over MgSO4. The organic solvent was evaporated in vacuo
to give a crude mixture of 1 and 1,5-Ac2AN in an 85:15 ratio. The
crude product was purified by repeated column chromatography
on silica gel 60, using petroleum ether (40–60 °C)–EtOAc as eluent,
from 98:2 to 80:20, followed by recrystallization from EtOAc. Com-
16. Adams, C. J.; Earle, M. J.; Roberts, G.; Seddon, K. R. Chem. Commun. 1998, 2097–
2098.
pound 1 was obtained as red crystals, mp 193 °C (lit., mp 182 °C27
)
17. Okamoto, A.; Yonezawa, N. Chem. Lett. 2009, 38, 914–915.
18. Agranat, I.; Bentor, Y.; Shih, Y.-S. J. Am. Chem. Soc. 1977, 99, 7068–7070.
19. Mala’bi, T.; Cohen, S.; Pogodin, S.; Agranat, I. Lett. Org. Chem. 2009, 6, 237–241.
20. Levy, L.; Pogodin, S.; Cohen, S.; Agranat, I. Lett. Org. Chem. 2007, 4, 314–318.
21. Bassilios, H. F.; Shawky, M.; Salem, A. Y. Recl. Trav. Chim. Pays-Bas 1962, 81,
679–682.
22. Bassilios, H. F.; Shawky, M.; Salem, A. Y. Recl. Trav. Chim. Pays-Bas 1963, 82,
298–301.
23. Sarobe, M.; Jenneskens, L. W. J. Org. Chem. 1997, 62, 8247–8250.
24. Duerr, B. F.; Chung, Y.-S.; Czarnik, A. W. J. Org. Chem. 1988, 53, 2120–2122.
25. Gore, P. H.; Thadani, C. K. J. Chem. Soc. C 1966, 1729–1733.
26. (E) and (Z) are the stereodescriptors applied to the acetylanthracene and
in 25% yield; MS, m/z = 244 (12C18H12O); IR, 1635 cmÀ1 (C@O); UV/
Vis (CHCl3, 1.4 Â 10À4 M nm): 489 sh (
e
7500), 462 (
e
8350), 442
25800)
sh, 370 (
e
7700), 354 sh (
e
7400), 269 (
e
26000), 241 (e
(lit., 462, 488 sh27). 1H NMR (500 MHz, CDCl3, ppm) d = 10.16
(dd, J1 = 9.0 Hz, J2 = 1.0 Hz, 1H, H11), 8.73 (s, 1H, H7), 8.13 (d,
J = 8.0 Hz, 1H, H6), 8.07 (dt, J1 = 8.3 Hz, J2 = 0.5 Hz, J3 = 1.0 Hz, 1H,
H8), 8.01 (dd, J1 = 7.2, J2 = 1.0 Hz, 1H, H4), 7.83 (ddd, J1 = 9.0 Hz,
J2 = 7.0 Hz, J3 = 1.5 Hz, 1H, H10), 7.61 (ddd, J1 = 8.3 Hz, J2 = 6.8 Hz,
J3 = 1.0 Hz, 1H, H9), 7.57 (dd, J1 = 8.5 Hz, J2 = 7.0 Hz, 1H, H5), 6.75
(d, J = 1.0 Hz, 1H, H2), 2.57 (d, J = 1.0 Hz, 3H, CH3). 13C NMR
(125 MHz, CDCl3, ppm) d = 187.8 (C1@O), 145.4 (C3), 137.4 (C7),
133.4 (C11a), 133.1 (C6), 132.2 (C7a), 131.7 (C10), 130.9 (C2), 129.8
(C4), 129.7 (C3a), 129.6 (C6a), 129.3 (C8), 128.3 (C11c), 127.8 (C11),
126.3 (C9), 125.0 (C5), 122.7 (C11b), 19.3 (CH3).
diacetylanthracene structures with
a fractional bond order of the bond
between the carbonyl carbon and the aromatic carbon.
27. Compound 1 has been described in the patent literature: DE 2,262,857 (A1)
(27.06.1974); Eiglmeier, K. Chem. Abstr. 1974, 81, 105112p (Accession Number
1974:505112).; GB 1,395,279 (A) (21.05.1975); Eiglmeyer, K. Chem. Abstr.
1974, 81, 120343h (Accession Number 1974:520343).; US 3,865,879 (A)
(11.02.1975); Eiglmeier, K. Chem. Abstr. 1973, 79, 137936k (Accession
Number 1973:537936).
28. Liljenberg, M.; Brinck, T.; Herschend, B.; Rein, T.; Rockwell, G.; Svensson, M. J.
Org. Chem. 2010, 75, 4696–4705.
Supplementary data
29. The calculations of the (Z,Z) and (E,Z) conformations of 1H,9-Ac2AN+1 lead to a
hemiketal, see Supplementary data.
Supplementary data (1H NMR spectrum of 1; total energies,
relative energies, and geometries of the diacetylanthracenes, their
30. Muller, P. Glossary of Terms Used in Physical Organic Chemistry (IUPAC
Recommendations 1994), Pure Appl. Chem. 1994, 66, 1077–1184.
O-protonates, their O,O-diprotonates and their
r-complexes) asso-
ciated with this article can be found, in the online version, at
doi:10.1016/j.tetlet.2011.02.026.