Friedel–Crafts acyl rearrangements in the fluoranthene series

Struct Chem (2017) 28:511–526

DOI 10.1007/s11224-016-0894-7

ORIGINAL RESEARCH

Friedel–Crafts acyl rearrangements in the fluoranthene series

Tahani Mala’bi¹& Shmuel Cohen¹& Sergey Pogodin¹& Israel Agranat¹

Received: 2 November 2016 /Accepted: 29 November 2016 /Published online: 15 December 2016

#

Springer Science+Business Media New York 2016

Abstract Friedel–Crafts monoacylation and diacylation of

fluoranthene (FT) gave 3-acetyl-, 8-acetyl-, 3-benzoyl-, 8-ben-

zoyl-, 3-(4-fluorobenzoyl)-, 8-(4-fluorobenzoyl)-, 3,9-diacetyl-,

3,9-dibenzoyl-, and 3,9-bis(4-fluorobenzoyl)fluoranthene (3-

AcFT, 8-AcFT, 3-BzFT, 8-BzFT, 3-(4-FBz)FT, 8-(4-FBz)FT,

3,9-Ac₂FT, 3,9-Bz₂FT, and 3,9-(4-FBz)₂FT). The crystal and

molecular structures of 8-AcFT, 3,9-Ac₂FT, 7,10-Ac₂FT, 3-

BzFT, 8-BzFT, and 3-(4-FBz)FT were determined by X-ray

crystallography. The structures of the fluoranthene derivatives,

including 3,9-Ac₂FT were verified by ¹H-, ¹³C-, and ¹⁹F-NMR

spectroscopy. The Friedel–Crafts acyl rearrangements in PPA

of the above fluoranthene derivatives were studied at various

temperatures and times. The kinetically controlled product 3-

AcFT/3-BzFT rearranged to the thermodynamically-controlled

product 8-AcFT/8-BzFT, not vice versa. 3,9-Ac₂FT, 3,9-Bz₂FT,

and 3,9-(4-FBz)₂FT underwent deacylation in PPA to give 8-

AcFT, 8-BzFT, and 8-(4-FBz)FT, respectively. Deacetylation of

3,9-Ac₂FT gave also 3-methyl-1H-benzo[cd]fluoranthene (3-

MeBcdFT). The rich Friedel–Crafts acylation chemistry in

PPA revealed in the fluoranthene series is characterized by re-

gioselectivity. DFT calculations at B3LYP/6-31G(d) supported

the regioselectivity including the formation of 3,9-Ac₂FT, and

the win of kinetic control over thermodynamic control.

.

Keywords X-ray crystallography NMR spectroscopy

.

Regioselectivity Deacylation Kinetic control

.

Thermodynamic control PPA DFT

Introduction

Friedel–Crafts alkylation and Friedel–Crafts acylation are con-

sidered cornerstones of organic chemistry [1, 2]. For many

years, it has been accepted that Friedel–Crafts acylations, in

contrast to Friedel–Crafts alkylations, are usually irreversible,

free of rearrangements, and isomerizations [1, 3, 4]. The differ-

ence in behavior between Friedel–Crafts acylation and Friedel–

Crafts alkylation was attributed to the resonance stabilization

existing between the acyl group and the aromatic nucleus [5],

which may serve as a barrier against rearrangements and revers-

ible processes. When the acyl group has been tilted out of the

plane of the aromatic nucleus, e.g., by neighboring bulky sub-

stituents, the resonance stabilization was reduced and the pattern

of irreversibility of Friedel–Crafts has been challenged [5–7].

In 1955, Gore introduced the concept of reversibility of

Friedel–Crafts acylation, proposing that BThe Friedel–Crafts ac-

ylation reaction of reactive aromatic hydrocarbons is a reversible

process^ [8]. Gore concluded that BReversibility is an important

factor in acylation reactions^ [8]. In 1964, Gore argued that in

polycyclic aromatic systems other than naphthalene, there is

This contribution is dedicated to Professor George A. Olah, the illustrious

scientist, the Doyen of Friedel–Crafts chemistry, in celebration of his

forthcoming 90th birthday.

Electronic supplementary material The online version of this article

(doi:10.1007/s11224-016-0894-7) contains supplementary material,

which is available to authorized users.

* Israel Agranat

isri.agranat@mail.huji.ac.il

Tahani Mala’bi

tahani.malabi@mail.huji.ac.il

Shmuel Cohen

shmuel.cohen2@mail.huji.ac.il

Sergey Pogodin

s.pogodin@mail.huji.ac.il

1

Organic Chemistry, Institute of Chemistry, The Hebrew University of

Jerusalem, Philadelphia Bldg. #212, Edmond J. Safra Campus,

9190410 Jerusalem, Israel

512

Struct Chem (2017) 28:511–526

direct experimental evidence in favor of reversibility [9]. The

reversibility studies have been focused mainly on unusual aspects

of selectivity, including deacylations, one-way rearrangements,

and kinetic versus thermodynamic control [7]. The incursion of

reversibility in Friedel–Crafts acylations was revealed by

Agranat, et al., in the benzoylation of naphthalene in

polyphosphoric acid (PPA) at elevated temperatures [10]. The

kinetically controlled 1-benzoylnaphthalene (1-BzNA)

rearranged to the thermodynamically controlled 2-

benzoylnaphthalene (2-BzNA) in PPA at 140 °C (vide infra),

whereas 2-BzNA underwent only deacylation, e.g., at 140 °C,

to give naphthalene (NA).

The reversibility concept was applied to the synthesis of

new linearly annelated polycyclic aromatic ketones, by intra-

molecular Friedel–Crafts acyl rearrangements of their angu-

larly annelated constitutional isomers [11–13]. Complete re-

versibility of Friedel–Crafts acylation was established in the

intramolecular ortho–para acyl rearrangements of 1-

fluorofluorenone ⇌ 3-fluorofluorenones in PPA [14].

Acyl rearrangements and reversibility in Friedel–Crafts acyl-

ations have been associated with thermodynamic control [6, 14].

Frangopol et al. [15] and Nenitzescu and Balaban [16, 17] have

reported the reversibility of Friedel–Crafts acetylation of olefins.

The contributions of kinetic control versus thermodynamic

control in Friedel–Crafts acyl rearrangements remain an open

question, in spite of the rich chemistry of Friedel–Crafts acyla-

tions [3, 8, 9]. We have recently reported that kinetic control wins

out over thermodynamic control in the Friedel–Crafts acyl rear-

rangements of diacetylanthracenes in PPA [18] and non-planarity

of the PAKs is not a sine qua non condition for the rearrange-

ments as in case of dibenzofluorenone [19]. The conformational

variations in these PAKs, which contribute to the understanding

of the motifs of reversibility, have been described [20, 21].

We report here the results of a study of the Friedel–Crafts acyl

rearrangements of acylfluoranthenes which includes mono- and

diacetylfluoranthenes, mono- and dibenzoylfluoranthenes, and

mono and bis(4-fluorobenzoyl)fluoranthenes in PPA.

spectra were recorded using ALPHA Bruker FTIR spectrometer

with an OPUS program using KBr. UV-Visible spectra were

recorded with a Varian UV-Visible spectrophotometer using

CHCl₃as solvent and as internal standard. Column chromatog-

raphy was performed using silica gel 60 (0.063–0.2 mm, 70–230

mesh ASTM) and appropriate solvents, the silica gel was obtain-

ed from Merck KGaA, Darmstadt, Germany. Mass spectra, LC-

MS, spectra were recorded with Accurate-Mass Q-TOF LC-MS

from Quaternary Agilent technologies using acetonitrile or

CHCl₃as a solvent. Elementary analyses for new polycyclic

aromatic ketones (PAKs) were carried out using Perkin Elemer

Preciesly, Series II, CHNS/O analyzer. LC-MS and Elementary

analyses were carried out by Dr. Carina Hazan, the microanalysis

laboratory, Institute of Chemistry, The Hebrew University of

Jerusalem. TLC R_fon silica gel 60 F₂₅₄plates was carried out

using PE (40–60 °C)/EtOAc 80:20 as eluent. PLC chromatogra-

phy on silica gel 60 F₂₅₄plates was obtained from E. Merck.

Fluoranthene (98%), benzoyl chloride, 4-fluorobenzoyl

chloride, acetyl chloride, AlCl₃, and polyphosphoric acid

(PPA; 84% weight of P₂O₅, density 1.9 g/ml) were obtained

from Acros Organics, Israel. All the solvents AR grades were

obtained from Bio-Lab Ltd., Israel. 7,10-diacetylfluoranthene

(7,10-Ac₂FT) was obtained from Akos Consulting and

Solutions Deutschland GmbH, Germany. Chloroform, dichlo-

romethane and 1,2-dichloroethane were dried on CaCl₂.

X-ray crystallography

Single crystal of each fluoranthene derivative was attached to

a 400/50 MicroMeshes™ with NVH Oil [23], and transferred

to a Bruker SMART APEX CCD X-ray diffractometer

equipped with a graphite-monochromator. Maintaining the

temperature at 173 K was done with a Bruker KRYOFLEX

nitrogen cryostat. The system was controlled by a Pentium-

based PC running the SMART software package [24]. Data

were collected at room temperature for 8-acetylfluoranthene

(8-AcFT), and at 173 K for the other fluoranthene derivatives

under study, using MoKα radiation (λ = 0.71073 Å).

Immediately after collection, the raw data frames were trans-

ferred to a second PC computer for integration and reduction

by the SAINT program package [25]. The structures were

solved and refined by the SHELXTL software package [26].

Experimental section

Melting points were uncorrected. NMR spectra were recorded

1

with Bruker Avance II 500 and AMX 400 spectrometers; H-

NMR spectra were recorded at 500.2 and 400.13 MHz in CDCl₃

as a solvent and as an internal standard, δ(CHCl₃) = 7.260 ppm.

¹³C-NMR spectra were recorded at 125.78 MHz using CDCl₃as

solvent and as internal standard, δ(CDCl₃) = 77.01 ppm, ¹⁹F-

NMR spectra were recorded at 470.66 MHz in CDCl₃as a

solvent and as an internal standard, δ(CHCl₃) = 7.260 ppm and

referenced and reported according to IUPAC Recommendations

2008 [22]. For comparison, the ¹⁹F-NMR chemical shift of

fluorobenzene in CDCl₃is −113.06 ppm. Complete assignments

were carried out through 2D correlation spectroscopy (COZY,

NOESY, HSQC, and HMBC) and recorded at 500.2 MHz. IR

Quantum mechanical calculations

The quantum mechanical calculations of the fluoranthene deriv-

atives under study were performed with the Gaussian 09 [27]

packages. Becke’s three-parameter hybrid density functional

B3LYP [28], with the non-local correlation functional of Lee

et al. [29] was used. The Pople style split valence 6-31G(d) basis

set was employed for geometry optimizations. All structures

were fully optimized, using symmetry constrains as indicated.

Vibration frequencies were calculated at B3LYP/6-31G(d) to

Struct Chem (2017) 28:511–526

513

verify the nature of the stationary points. Non-scaled thermal

corrections to enthalpy and to free-energy calculated at the same

levels were applied. Calculations in the solvent reaction field

(SCRF) were performed using the polarizable continuum model

(PCM) with formic acid as solvent, as implemented in Gaussian

09 [30].

in dry CH₂Cl₂(150 ml) at 0 °C, acetyl chloride (6.4 ml,

99.0 mmol) and then AlCl₃(17.8 g, 128.3 mmol) were added.

The reaction mixture was stirred for 1 h at 0 °C and then for

4 h at RT. The work-up was carried out according to the

procedure described above. Column chromatography on silica

gel of the crude product using PE/EtOAc 98:2 as eluent gave

6 g of pure 3,9-Ac₂FT, yield 42%, mp. 139–140 °C (lit 137–

139 °C [31, 34]), TLC R_f= 0.26. A single crystal of 3,9-

Ac₂FT was obtained by recrystallization from EtOH_.

Procedures

8-Acetylfluoranthene (8-AcFT) and 3-acetylfluoranthene (3-

AcFT) were prepared according to a literature procedure [31]

with slight modifications. Fluoranthene (10 g, 49 mmol) was

dissolved in dry CH₂Cl₂and treated with acetyl chloride

(4.4 ml, 64 mmol). The reaction mixture was cooled to 0 °C.

AlCl₃(8.5 g, 64 mmol) was then added in one portion. The

reaction mixture was stirred for 1 h in ice bath then 4 h at rt. The

complex was decomposed with cold dilute aqueous HCl (or

cold H₂O). The reaction product was extracted with CH₂Cl₂,

washed with H₂O and NaHCO₃(aq), dried over MgSO₄, and

the organic solvent was evaporated under reduced pressure.

The resulting crude product (7.0 g) contained 3-AcFT and 8-

AcFT in the ratio of 35:65. Column chromatography of the

crude product on silica gel using PE/EtOAc 99:1% as eluent

gave the first fraction, 2.0 g of 3-AcFT, yield 17.0%, mp. 128–

129 °C (lit. 127–129 °C [31, 32]); TLC R_f= 0.60. The second

fraction contained 8-AcFT, 3.0 g, yield 25.0%, mp. 102–103 °C

(lit. 101–102 °C [31–33]), TLC R_f= 0.51. A single crystal of 8-

AcFT was obtained by recrystallization from EtOAc.

¹H-NMR δ(CDCl₃, ppm)—8.86 (dd, ³J = 8.5 Hz,

⁵J = 0.5 Hz, 1H, H⁴), 8.48 (s, 1H, H¹⁰), 8.22 (d,

3

4

³J = 7.0 Hz, 1H, H²), 8.03 (dd, J = 7.75 Hz, J = 2.0 Hz,

⁴J = 1.5 Hz, 1H, H⁸), 8.00 (d,³J = 7.5 Hz, 1H, H¹), 7.98 (dd,

³J = 7.0 Hz, J = 1.0 Hz, 1H, H⁶), 7.92 (dd, J = 9.0 Hz,

4

3

⁵J = 0.5 Hz, 1H, H⁷),7.74 (dd, ³J = 8.0 Hz, ⁴J = 2.0 Hz, 1H,

H⁵), 2.80 (s, 3H, CH₃), and 2.71 (s, 3H, CH₃). ¹³C-NMR

δ(CDCl₃, ppm)—200.4 (C¹³), 197.6 (C¹¹), 144.7 (C^10a),

140.8 (C^10b), 138.3 (C³), 136.5 (C⁸), 135.7 (C^6a), 134.1

(C^6b), 133.8 (C^10c), 132.2 (C²), 130.3 (C⁵), 129.6 (C⁹),

128.5 (C⁴), 127.9 (C^3a), 122.0 (C¹), 121.9 (C⁷), 121.3 (C¹⁰),

119.4 (C⁶), 29.1 (C³H₃), and 26.9 (C⁹H₃).

3

9

8 - B e n z o y l f l u o r a n t h e n e ( 8 - B z F T ) a n d 3 -

benzoylfluoranthene (3-BzFT) were prepared according to a

literature procedure [32] with slight modifications. To a solu-

tion of fluoranthene (10 g, 49 mmol) at 0 °C in dry CH₂Cl₂

(150 ml), benzoyl chloride (7.5 ml, 64 mmol) was added

followed by AlCl₃(8.5 g, 64 mmol). The reaction mixture

was left with stirring at 0 °C for 1 h then at RT for 4 h. The

work-up was carried out according to the procedure described

above. The crude product which consisted of a mixture of 3-

BzFT and 8-BzFT in the ratio of 18:25, were subjected to

column chromatography on silica gel using PE/EtOAc 99:1

as eluent. The first fraction was collected to give 2.5 g of 3-

BzFT, yield 17.0%, mp. 130–131 °C (lit. 129–130 °C [32]),

TLC R_f= 0.69. The second fraction contained 3 g of 8-BzFT,

yield 25.0% mp. 120–121 °C (lit. 120–121 °C [32]); TLC

R_f= 0.49. Single crystals of 8-BzFT and 3-BzFT were obtain-

ed by recrystallizations from EtOAc and CHCl₃, respectively.

1

3-AcFT H-NMR δ(CDCl₃, ppm)—8.77 (d, ³J = 8.5 Hz, 1H,

H⁴), 8.17 (d, ³J = 7.5 Hz, 1H, H²), 7.91 (d, ³J = 8.0 Hz, 1H, H¹),

7.89–7.88 (m, 2H, H⁶, H¹⁰), 7.86 (dd, ³J = 7.5 Hz, ⁴J = 1.0 Hz,

3

⁵J = 0.5 Hz, 1H, H⁷), 7.68 (td, J = 6.5 Hz, J = 7.0 Hz,

⁴J = 2.0 Hz, 1H, H⁵), 7.43 (td, J = 7.5 Hz, J = 7.25 Hz,

3

⁴J = 1.5 Hz, 1H, H⁸), 7.35 (td,³J = 7.5 Hz, J = 7.25 Hz,

3

⁴J = 1.5 Hz, 1H, H⁹), and 2.79 (s, 3H, CH₃). ¹³C-NMR

δ(CDCl₃, ppm)—200.4 (C¹¹), 141.9 (C^10b), 140.6 (C^6b), 138.1

(C^10a), 137.0 (C^6a), 133.8 (C³), 133.0 (C^10c), 132.0 (C²), 130.2

(C⁵), 128.9 (C¹⁰), 127.9 (C^3a), 127.8 (C⁷), 127.1 (C⁴), 122.3 (C⁸),

121.6 (C⁹), 120.6 (C⁶), 118.5 (C¹), and 29.1 (CH₃).

3-BzFT ¹H-NMR δ(CDCl₃, ppm)—8.17 (d, ³J = 8.5 Hz, 1H,

H⁴), 7.95 (dd, ³J = 7.5 Hz, ⁴J = 3.0 Hz, 2H, H¹, H⁶), 7.93–7.92

8-AcFT ¹H-NMR δ(CDCl₃, ppm)—8.49 (s, 1H, H⁷), 8.02 (2d,

³J = 7.0 Hz, 2H, H¹, H⁶), 7.99 (dd, ³J = 8.5 Hz, ⁴J = 1.5 Hz,

1H, H⁹), 7.95 (d, ³J = 8.0 Hz, 1H, H¹⁰), 7.92 (d, ³J = 8.0 Hz,

3

(m, H⁷, H¹⁰), 7.89 (d, J = 7.5 Hz, 2H, H^2′, H^6′), 7.85

(d,³J = 7.0 Hz, 1 Hz, H²), 7.66 (td, ³J = 7.5 Hz, ⁴J = 1.5 Hz,

1H, H⁵), 7.62 (t, ³J = 7.0 Hz, ³J = 7.5 Hz, 1H, H^4′), 7.45 (t,

3

1H, H³), 7.89 (d, J = 8.0 Hz, 1H, H⁴), 7.68 (t, J = 7.5 Hz,

J = 7.5 Hz, 2H, H², H⁵), and 2.71 (s, 3H, CH₃). ¹³C-NMR

³J = 7.5, J = 8 Hz, 2H, H^3′, H^5′), 7.44 (td, J = 7.25 Hz,

³J = 8.5 Hz, ⁴J = 1.5 Hz, 1H, H⁸), and 7.40 (td, ³J = 8.5 Hz,

³J = 7.5 Hz, 1 Hz, H⁹). ¹³C-NMR δ(CDCl₃, ppm)—197.2

(C¹¹), 140.6 (C^10b), 140.3 (C^6b), 138.8 (C^1′), 136.5 (C^10a),

137.1 (C^6a), 132.9 (C^10c), 132.9 (C^4′), 132.7 (C³), 131.8

(C²), 130.4 (C^2′, C^6′), 129.5 (C⁵), 128.7 (C⁸), 128.5 (C^3a),

128.4 (C^3′, C^5′), 127.8(C⁹), 126.0 (C⁴), 122.2 (C¹⁰), 121.7

(C⁷), 120.7 (C⁶), and 118.4 (C¹).

3

δ(CDCl₃, ppm)—197.9 (C¹¹), 143.6 (C^10a), 139.6 (C^3a), 136.6

(C^6b), 136.0 (C^6a), 135.7 (C⁸), 133.2 (C^10c), 129.6 (C^10b), 128.3

(C²), 128.2 (C⁹), 128.1 (C¹⁰), 127.9 (C³), 127.2 (C⁴), 121.4

(C¹), 121.2 (C⁶), 121.2 (C⁷), 120.8 (C⁵), and 26.8 (CH₃).

3,9-Diacetylfluoranthene (3,9-Ac₂FT) was prepared ac-

cording to a literature procedure [31] with slight modifica-

tions. To a cooled solution of fluoranthene (10 g, 49 mmol)

514

Struct Chem (2017) 28:511–526

8-BzFT ¹H-NMR δ(CDCl₃, ppm)—8.40 (s, 1H, H⁷), 8.07 (d,

³J = 7.0 Hz, 1H, H⁶), 8.02 (d, ³J = 7.0 Hz, 1H, H¹), 8.01 (d,

³J = 8.0 Hz, 1H, H¹⁰), 7.95 (d, ³J = 8.5 Hz, 1H, H⁴), 7.92 (d,

³J = 8.5 Hz, 1H, H³), 7.89 (2d, ³J = 7.5 Hz, 2H, H^2′, H^6′), 7.86

(dd, ³J = 8.5 Hz, ⁴J = 1.5 Hz, 1H, H⁹), 7.71 (t, ³J = 7.5 Hz,

³J = 8.5 Hz, 1H, H⁵), 7.69 (t, ³J = 8.5 Hz, ³J = 8.5 Hz, 1H, H²),

was obtained by recrystallization from EtOAc. Elementary anal-

ysis: calculated for 8-(4-FBz)FT (C₂₃H₁₃FO): C = 84.45%,

H = 3.95%, F = 6.15%; found: C = 84.24%, H = 3.99%,

F = 5.30%. MS: m/z = 325 (M⁺¹); IR, 1645.61 cm⁻¹(C=O);

UV/VIS (nm): 385, 368 and 327. The crude product from the

filtrate was subjected to column chromatography on silica gel

using PE/EtOEt 99:1 to give 2. 5 g of 3-(4-

fluorobenzoyl)fluoranthene (3-(4-FBz)FT) as a yellow powder,

yield 17.0%, mp. 187.8–188.5 °C; TLC R_f= 0.71. A single

crystal of 3-(4-FBz)FT was obtained by recrystallization from

EtOAc. Elementary analysis: calculated for 3-(4-FBz)FT

(C₂₃H₁₃FO): C = 85.17%, H = 4.04% and F = 5.86%; found:

C = 84.24%, H = 3.99% and F = 5.30%. MS, m/z = 325(M⁺¹);

IR: ν = 1641.55 cm⁻¹(C=O); UV/vis (nm): λ = 392, 368, and

338.

7.63 (t, J = 7.5 Hz, J = 7.5 Hz, 1H, H^4′), and 7.54 (t,

³J = 7.5 Hz, ³J = 7.5 Hz, 2H, H^3′, H^5′). ¹³C-NMR δ(CDCl₃,

ppm)—196.7(C¹¹), 143.2 (C^10a), 139.4 (C^6b), 138.1 (C^1′),

136.7 (C⁸), 136.1 (C^10b), 135.8 (C^6a), 133.2 (C^10c), 132.3

(C^4′), 130.2 (C⁹), 130.1 (C^3a), 130.0 (C^2′, C^6′), 128.3

(C^3′,C^5′), 128.3 (C²), 128.2 (C⁵), 127.9 (C⁴), 127.3 (C³),

123.2 (C⁷), 121.5 (C⁶), 121.0 (C¹⁰), and 120.9 (C¹).

3

3,9-Dibenzoylfluoranthene (3,9-Bz₂FT) A suspension of

AlCl₃(3.5 g, 26.4 mmol) and benzoyl chloride (3.1 ml,

26.4 mmol) in dry ClCH₂CH₂Cl (150 ml) was heated to

80 °C. 8-BzFT (3.0 g, 10.7 mmol) was then added, and the

reaction was stirred overnight at 80 °C. The work-up was carried

out according to the procedure described above. Column chro-

matography on silica gel of the crude product using PE/EtOAc

99:1 as eluent gave 1.0 g of 3,9-dibenzoylfluoranthene (3,9-

Bz₂FT) as a pale yellow powder, yield 22.0%, mp. 159–

160 °C, TLC R_f= 0.49. Elementary analysis: calculated for

C₃₀H₁₈O₂: C = 87.78% and H = 4.42%. Found: C = 87.37%,

H = 4.34%. MS, m/z = 411.138 (M⁺¹); IR: ν = 1653.18 cm⁻¹

(C=O); UV/vis (nm): λ = 391, 368, and 328.

3-(4-FBz)FT ¹H-NMR δ(CDCl₃, ppm)—8.10 (d, ³J = 8.5 Hz,

1H, H⁴), 7.95 (2d, ³J = 7.0 Hz, 2H, H¹, H⁶), 7.93 (d, ³J = 6.0 Hz,

3

2H, H^2′, H^6′), 7.89 (d, J = 9.5 Hz, 2H, H⁸, H⁹), 7.82 (d,

³J = 7.0 Hz, 1H, H²), 7.65 (td, ³J = 6.5 Hz, ⁴J = 2.0 Hz, 1H,

H⁵), 7.44 (td, ³J = 8.0 Hz, ³J = 7.0 Hz, ⁴J = 1.0 Hz, ⁴J = 1.5 Hz,

3

⁴J = 2.0 Hz, 1H, H⁷), 7.41 (td, J = 8.0 Hz, J = 8.0 Hz,

⁴J = 1.0 Hz, J = 1.5 Hz, J = 2.0 Hz, 1H, H¹⁰), and 7.17

(t,³J = 7.5 Hz, ³J = 7.5 Hz, 2H, H^3′, H^5′). ¹³C-NMR δ(CDCl₃,

ppm)—195.5 (C¹¹), 165.7 (C^4′), 140.7 (C^10b), 140.3 (C^10a),

138.5 (C^6b), 137.2 (C^6a), 135.1 (C^1′), 134.8 (C^10c), 133.0 (C^2′,

C^6′), 132.8 (C³), 131.4 (C²), 129.5 (C⁵), 128.7 (C⁷), 128.4 (C^3a),

127.9 (C¹⁰), 125.8 (C⁴), 122.2 (C⁹), 121.7 (C⁸), 120.8 (C⁶), 118.4

(C¹), and 115.7 (C^3′, C^5′). ¹⁹F-NMR δ(CDCl₃, ppm)—−105.26.

4

¹H-NMR δ(CDCl₃, ppm)—8.46 (s, 1H, H¹⁰), 8.26 (d,

3

³J = 8.5 Hz, 1H, H⁴), 8.06 (d, J = 7.0 Hz, 1H, H⁶), 8.01 (d,

³J = 7.0 Hz, 1H, H¹), 8.00 (d, ³J = 7.5 Hz, 1H, H⁷), 7.91–7.78 (m,

6H, H², H⁸, H^2′, H^2″, H^6′, H^6″), 7.72 (td, ³J = 8.0 Hz, ⁴J = 1.5 Hz,

8-(4-FBz)FT ¹H-NMR δ(CDCl₃, ppm)—8.36 (s, 1H, H⁷), 8.07

(d, ³J = 7.0 Hz, 1H, H¹), 8.02 (d,³J = 6.5 Hz, 1H, H⁶), 8.01 (d,

³J = 7.5 Hz, 1H, H¹⁰), 7.95 (2d, ³J = 8.0 Hz, 2H, H³, H⁴), 7.92

3

4

1H, H⁵), 7.64 (td, J = 8.5 Hz, J = 6.5 Hz, J = 1.5 Hz,

⁴J = 1.0 Hz, 2H, H^4′, H^4″), 7.52 (t, ³J = 7.25 Hz, ³J = 8.0 Hz,

2H, H^3′, H^3″), 7.51 (t, ³J = 7.0 Hz, ³J = 8.5 Hz, 2H, H^5′, H^5″). ¹³C-

NMR δ(CDCl₃, ppm)—196.9 (C¹³), 196.5 (C¹¹), 143.9 (C^10a),

139.5 (C^10b), 138.5 (C^1″), 138.5 (C^10c), 137.9 (C^1′), 137.0 (C⁸),

135.9 (C^6a), 135.5 (C³), 133.5 (C^6b), 133.1 (C^4′), 132.4 (C^4″),

131.8 (C²), 131.2 (C⁹), 130.4 (C^2′, C^6′), 130.0 (C^2″, C^6″),

129.6(C⁵), 128.5 (C^3a), 128.5 (C^3′, C^5′), 128.4 (C^3″, C^5″), 127.2

(C⁴), 123.7 (C⁷), 122.1 (C⁶), 121.2 (C¹⁰), and 119.3 (C¹).

3

4

(dd, J = 7.0 Hz, J = 1.5 Hz, 2H, H^3′, H^5′), 7.82 (dd,

³J = 7.0 Hz, J = 1.5 Hz, 1H, H⁹), 7.71 (t, J = 8.0 Hz,

4

3

³J = 8.0 Hz, 1H, H²), 7.69 (t, J = 8.0 Hz, J = 8.0 Hz, 1H,

3

H⁵), and 7.21 (t, J = 8.5 Hz, J = 8.5 Hz, 2H, H^2′, H^6′). ¹³C-

NMR δ(CDCl₃, ppm)—195.3 (C¹¹), 165.4 (C^4′), 143.3 (C^10a),

139.5 (C^6b), 136.6 (C⁸), 136.0 (C^6a), 135.8 (C^10b), 134.3 (C^1′),

133.2 (C^10c), 132.6 (C^3′, C^5′), 130.1 (C^3a), 130.0 (C⁹), 128.3 (C⁵),

128.2 (C²), 128.0 (C³), 127.4 (C⁴), 123.0 (C⁷), 121.5 (C¹), 121.1

(C¹⁰), 121.0 (C⁶), and 115.6 (C^2′, C^6′). ¹⁹F-NMR δ(CDCl₃,

ppm)—−106.25.

3

3-(4-Fluorobenzoyl)fluoranthene (3-(4-FBz)FT) and 8-(4-

fluorobenzoyl)fluoranthene (8-(4-FBz)FT) Fluoranthene

(10.0 g, 49 mmol) was dissolved in dry CH₂Cl₂(150 ml) and

treated with 4-fluorobenzoyl chloride (10.1 ml, 68 mmol); the

reaction mixture was cooled to 0 °C, AlCl₃(8.6 g, 64 mmol) was

then added in one portion. The reaction mixture was left with

stirring for 1 h in 0 °C then for 4 h at rt. The precipitate was

filtered off and both the filtrate and the precipitate were

decomposed using cold dilute aqueous HCl. The crude product

from the precipitate was recrystallized from PE to give 8-(4-

fluorobenzoyl)fluoranthene (8-(4-FBz)FT), 3.5 g, yield 22.0%,

mp. 143–144 °C, TLC R_f= 0.74. A single crystal 8-(4-FBz)FT

3,9-Bis(4-fluorobenzoyl)fluoranthene (3,9-(4-FBz)₂FT) To

a suspension of AlCl₃(3.3 g, 26.4 mmol) and 4-fluorobenzoyl

chloride (3.9 ml, 25 mmol) in dry ClCH₂CH₂Cl (150 ml) at

80 °C, 8-(4-FBz)FT (3.0 g, 9.3 mmol) was added. The reaction

was stirred at 80 °C overnight. The work-up was carried out

according to the procedure described above. Column chroma-

tography on silica gel of the crude product using PE/EtOAc 99:1

gave 0.67 g of 3,9-bis(4-fluorobenzoyl)fluoranthene (3,9-(4-

FBz)₂FT) as a pale yellow powder, yield 15.0%, mp. 184.1–

Struct Chem (2017) 28:511–526

515

185.5 °C. TLC R_f= 0.59. Single crystal of 3,9-(4-FBz)₂FT was

obtained by recrystallization from CDCl₃. Elementary analysis:

calculated for 3,9-(4-FBz)₂FT (C₃₀H₁₁F₂O₂): C = 80.71,

H = 3.61 and F = 8.51%; found: C = 80.19, H = 3.60 and

F = 8.00%. MS: m/z = 446.11(M⁺¹); IR: ν = 1646.92 cm⁻¹

(C=O); UV/vis (nm): λ = 383, 368, and 316.

ratio, to give 0.1 g of 3-MeBcdFT as pure red powder, in 11%

yield, mp. 209–210 °C; TLC R_f= 0.48; MS: m/z = 269 (M⁺¹);

IR: ν = 1641 cm⁻¹(C=O); UV/vis (nm): λ = 432, 414, 387 sh,

348 sh, 307 sh, 295 sh, and 247.

¹H-NMR δ(CDCl₃, ppm)—8.32 (d, ³J = 7.0 Hz, 1H, H¹¹),

3

7.80 (d, J = 7.0 Hz, 1H, H¹⁰), 7.71–7.67 (m, 2H, H⁶, H⁹),

¹H-NMR δ(CDCl₃, ppm)—8.389 (s, 1H, H¹⁰), 8.21 (d,

7.66 (s, 2H, H⁴, H⁵), 7.29–7.27 (m, 2H, H⁷, H⁸), 6.34 (2,

⁴J = 1 Hz,1H, H²), and 2.42 (d, ³J = 1.5 Hz, 3H, CH₃). ¹³C-

NMR δ(CDCl₃, ppm)—185.1 (C=O), 148.9 (C^3a), 143.4

(C^9b), 140.6 (C^5b), 140.3 (C^5a), 140.2 (C^9a), 133.0 (C^9c),

130.7 (C¹¹), 130.4 (C^11a), 129.3 (C²), 129.1 (C⁷), 129.0

(C⁸), 128.9 (C³), 128.6 (C⁴, C⁵), 126.7 (C^11b), 123.0 (C⁹),

122.8 (C⁶), 120.6 (C⁴, C⁵), 120.5 (C¹⁰), and 22.9 (CH₃).

3

³J = 8.5 Hz, 1H, H⁴), 8.08 (d, J = 7.0 Hz, 1H, H⁶), 8.03 (d,

³J = 7.0 Hz, 1H, H¹), 8.02 (d, ³J = 7.5 Hz, 1H, H⁷), 7.99–7.92 (m,

4H, H^2′, H^6′, H^2″,H^6″), 7.86 (d, ³J = 7.0 Hz, 1H, H²), 7.86 (dd,

4

3

³J = 7.5 Hz, J = 1.5 Hz, 1H, H⁸), 7.73 (td, J = 7.75 Hz,

J = 7.5 Hz, J = 1.5 Hz, 1H, H⁵), 7.22 (t, J = 8.5 Hz,

3

4

3

J = 8.5 Hz, 2H, H^3″, H^5″), and 7.19 (t, J = 8.5 Hz,

3

J = 9.0 Hz, 2H, H^3′, H^5′). ¹³C-NMR δ(CDCl₃, ppm)—

195.2(C¹¹), 194.9(C¹³), 166.6 (C^4′), 164.6 (C^4″), 143.8 (C^10a),

139.4 (C^10b), 138.4 (C³), 136.8 (C⁸), 135.8 (C^6a), 135.3 (C^6b),

134.8 (C^1″), 134.0 (C^1′), 133.4 (C^10c), 133.0 (C^2″, C^6″), 132.6

(C^2′, C^6′), 131.3 (C⁹), 131.0 (C²), 129.6 (C⁵), 128.3 (C^3a),

127.0 (C⁴), 123.5 (C⁷), 122.1 (C⁶), 121.2 (C¹⁰), 119.3 (C¹),

115.7 (C^3″, C^5″), and 115.5 (C^3′, C^5′). ¹⁹F-NMR δ(CDCl₃,

ppm)—−104.74 and −105.78.

Acyl rearrangement of 8-acetyl fluoranthene The reaction

was carried out in a 150-ml round-bottomed flask with a mag-

netic stirrer and anhydrous argon atmosphere, protected from

moisture. PPA (133 g) was added. After stirring for few minutes

at 120 °C, 8-AcFT (1.0 g, 3.4 mmol) was added. The reaction

mixture was stirred at 120 °C for 2 h, and then was poured into a

mixture of ice and water and stirred overnight. The products were

extracted with CH₂Cl₂, the organic fraction were washed with

saturated NaHCO₃and water, and dried over MgSO₄. The or-

ganic solvent was evaporated in vacuum to give a mixture of

both 3-AcFT and 8-AcFT. Two new compounds were formed at

reaction temperatures higher than 120 °C. Separation of the com-

pound I was performed by PLC on silica gel, using PE/EtOAc as

eluent.

Acyl rearrangements of acetylfluoranthenes,

diacetylfluoranthenes, benzoylfluoranthenes,

dibenzoylfluoranthenes, fluorobenoylfluoranthene, and

bis(fluorobenzoyl)fluoranthene. In a 150-ml round-bottomed

flask equipped with a magnetic stirrer and argon gas. PPA (40 g)

was heated with stirring for a few minutes at a desired tempera-

ture; 0.3 g of acylfluoranthene, diacylfluoranthene, or

bis(fluorobenzoyl)fluoranthene was then added. The reaction

mixture was stirred for an appropriate time. It was then poured

into ice and H₂O and stirred overnight in order to hydrolyze the

complex and PPA and to facilitate the extraction of the organic

compounds. The reaction product was extracted with CH₂Cl₂,

washed with saturated aqueous NaHCO₃and H₂O, dried over

MgSO₄, filtered, and the organic solvent was evaporated in vac-

uum to give the crude products. These were detected and identi-

fied according to their selected ¹H-NMR chemical shifts.

Compound I ¹H-NMR (δCDCl₃, ppm)—8.47 (s, H⁷), 8.08 (d,

J = 6.5 Hz, H⁶), 8.05 (d, J = 8.0 Hz, H¹⁰), 8.03 (d, J = 7.0 Hz,

H¹), 7.95 (d, J = 6.5 Hz, H³), 7.94 (d, J = 7.5 Hz, H⁹), 7.91 (d,

J = 8.5 Hz, H⁴), 7.72 (t, J = 7.5 Hz, 7.5 Hz, H²), and 7.69 (t,

J = 8.0 Hz, 8.5 Hz, H⁵). ¹³C-NMR (δCDCl₃, ppm)—δ = 196.7

(C=O), 143.1 (C^10b), 139.5 (C^7a), 137.2 (C⁸), 136.1 (C⁷), 135.9

(C^10a), 133.2 (C⁶), 130.1 (C³), 130.1 (C⁴), 128.3 (C⁵), 128.2 (C²),

127.9 (C⁹), 127.3 (C⁴), 123.2 (C⁷), 121.4 (C¹), 121.1 (C¹⁰), and

121.0 (C⁶). LC-MS: m/z = 633 and 431 (M⁺¹).

Acyl rearrangement of 3,9-Ac₂FT. The reaction was carried

out in a 150-ml round-bottomed flask with a magnetic stirrer and

anhydrous argon atmosphere, protected from moisture. PPA

(133 g) was added. After stirring for few minutes at 120 °C,

3,9-Ac₂FT (1.0 g, 3.4 mmol) was added. The reaction mixture

was stirred at 120 °C for 2 h, and then was poured into a mixture

of ice and water and stirred overnight. The products were extract-

ed with CH₂Cl₂, the organic fraction were washed with saturated

NaHCO₃and water, and dried over MgSO₄. The organic solvent

was evaporated in vacuum to give a mixture that consisted of 3,9-

Ac₂FT, 8-AcFT, and FT in the ratios 59:16:25 and 3-

methylbenzo[c,d]fluoranthene (3-MeBcdFT). The crude product

(0.7 g) was purified by column chromatography on silica gel

using PE/EtOAc as eluent, starting with 98:2 and then 20:80

Acyl rearrangements of fluorobenzoylfluoranthenes and

3,9-bis(fluorobenzoyl)fluoranthene (general procedure).

In a 150-ml round-bottomed flask equipped with a magnetic

stirrer and argon and protected from the moisture, PPA (40 g)

was heated with stirring for few minutes at a desired tem-

perature. Selected fluorobenzoylfluoranthene or 3,9-

bis(fluorobenzoyl)fluoranthene (0.3 g) was added. The reaction

mixture was stirred for an appropriate time. It was then poured

into ice and H₂O and stirred overnight in order to hydrolyze the

PPA and to facilitate the extraction of the organic compounds.

The reaction products were extracted with CH₂Cl₂, washed with

saturated aqueous NaHCO₃and H₂O, dried over MgSO₄, fil-

tered, and the organic solvent was evaporated in vacuum to give

the crude products. These were detected and identified according

516

Struct Chem (2017) 28:511–526

to their selected ¹H-NMR chemical shifts. Column chromatog-

raphy using appropriate solvent was used to separate the resulted

products of the rearrangements.

literature [31, 32, 37–39]. The present study describes in ad-

dition the synthesis of 3,9-Bz₂FT, 3-(4-FBz)FT, 8-(4-FBz)FT,

and 3,9-(4-FBz)₂FT. The structures of 8-AcFT, 8-BzFT, 3-

BzFT, 3-(4-FBz)FT, 3,9-Ac₂FT, and 7,10-Ac₂FT have been

verified by X-ray crystallography (vide infra) [40].

Results and discussion

3-(4-FBz)FTand 8-(4-FBz)FTwere synthesized by treatment

of FT with 4-fluorobenzoyl chloride and AlCl₃in CH₂Cl₂at

0 °C for 4 h. The constitutional isomers were separated using

column chromatography to give 17% of 3-(4-FBz)FT, mp. 188–

189 °C, and 22% 8-(4-FBz)FT, mp. 143–144 °C.

Fluoranthene (FT) is a non-alternant polycyclic aromatic hydro-

carbon (PAH) with C_2vsymmetry, in which a naphthalene ring

and a benzene ring are fused together to give a peri-condensed

C₆C₆C₆C₅ring system. The Kekulé structures in fluoranthenes

have been systematically analyzed [35]. Fluoranthenes

possessing Kekulé structures were classified into three types,

depending on the nature of the two C–C bonds connecting ben-

zene and naphthalene fragments. Fluoranthene has five non-

equivalent sites for mono substitution: 1, 2, and 3 at the naphtha-

lene ring and 7 and 8 at the benzene ring. Electrophilic aromatic

substitution has been shown to take place at the naphthalene ring

at position 3 (α-position), and/or at the benzene ring at position 8,

farther away from the Bbay^ regions. Monoacylation of fluoran-

thene gave only 3-acylfluoranthene and 8-acylfluoranthene [31,

32]. These monoacylfluoranthenes differ in their degree of over-

crowding. The acyl group at position 3 is overcrowded due to the

peri-hydrogen (H⁴); the acyl group at position 8 is considered

non - overcrowded; it is flanked by two ortho hydrogens (H⁷,

H⁹). Friedel–Crafts acylations at positions 1 and 7 do not take

place due to the overcrowded bay regions. Moreover, position 2

resembles the β-position of naphthalene; it is less reactive toward

electrophilic attack than position 3 (α-position). Dewar-PI MO

study of electrophilic aromatic substitution in fluoranthene and

it’s σ-complexes correctly predicted that fluoranthene undergoes

electrophilic substitution preferentially at position 3 [36].

3,9-Bz₂FT and 3,9-(4-FBz)₂FT were prepared by the reac-

tions of 8-BzFT/8-(4-FBz)FT, benzoyl chloride/4-

fluorobenzoyl chloride, and AlCl₃in 1,2-dichloroethane at

80 °C for 14 h. 3,9-Bz₂FT and 3,9-(4-FBz)₂FT were purified

by column chromatography. 3,9-Bz₂FTwas obtained as a yel-

low product, 22% yield, mp. 159–160 °C. 3,9-(4-FBz)₂FT

was obtained as a pale yellow, yield 15%, mp. 184–186 °C.

In the present study, the reaction of 8-AcFT, acetyl chloride

and AlCl₃in dry CH₂Cl₂starting at 0 °C, then at room

temperature for 1 h gave one constitutional isomer of

diacetylfluoranthene, 3,9-Ac₂FT. mp. 139–140 °C (lit. 137–

139 °C [31, 34]). The same isomer was obtained by the analo-

gous acetylation of 3-AcFT. The previous reported studies of

Friedel–Crafts acetylation of 3-AcFT and 8-AcFT, with 2.3

equivalents of acetyl chloride and AlCl₃in CH₂Cl₂for 4 h at

room temperature gave 42% of a diacetylfluoranthene, without

unequivocally determining its exact structure [31, 41]. We note

that the Friedel–Crafts acetylations of 3-AcFT and 8-AcFT to

give 3,9-Ac₂FT were regioselective.

NMR spectroscopy

There are 25 constitutional isomers of a diacylfluoranthene.

These may be classified on the basis of the positions of the acyl

substituents: (i) diacylfluoranthene in which the two acyl

groups are positioned at the naphthalene ring system; (ii)

diacylfluoranthene in which one acyl group is positioned at

the naphthalene ring and the second acyl is positioned at the

benzene ring; and (iii) diacylfluoranthene in which the two acyl

groups are positioned at the benzene ring. Diacylfluoranthenes

of group (ii) have been claimed to be synthesized by

Friedel–Crafts diacylation of fluoranthene giving 3,8-

diacylfluoranthene and/or 3,9-diacylfluoranthene [31, 34].

The present study encompasses the following mono- and

diacylfluoranthenes: 3-AcFT, 8-AcFT, 3,9-Ac₂FT, 7,10-

Ac₂FT, 3-BzFT, 8-BzFT, 3,9-Bz₂FT, 3-(4-FBz)FT, 8-(4-

FBz)FT, and 3,9-(4-FBz)₂FT (Fig. 1).

The structures of AcFTs, BzFTs and (4-FBz)FTs have been

verified by ¹H- and ¹³C-NMR spectra. Table 1 gives the ¹H-

NMR chemical shifts of AcFTs, BzFTs, and (4-FBz)FTs.

Table 2 gives the ¹H-NMR chemical shifts of hydrogens peri

and ortho to the carbonyl, ¹³C-NMR chemical shifts of the

carbonyl group, and ¹⁹F-NMR chemical shifts.

In 3-AcFT, 3-BzFT, and 3-(4-FBz)FT, the hydrogens located

peri to the carbonyl group (H⁴) are deshielded more than the

hydrogens ortho to the carbonyl group (H²). Both H²and H⁴

were considerably deshielded as compared with the hydrogens of

unsubstituted FT. The differences in the chemical shifts between

the hydrogens peri and ortho to the carbonyl to those of

unsubstituted FT are noted: Δδ(H⁴) = 0.92 ppm,

Δδ(H²) = 0.53 ppm (3-AcFT), Δδ(H⁴) = 0.32 ppm,

Δδ(H²) = 0.24 ppm (3-BzFT), and Δδ(H⁴) = 0.26 ppm,

Δδ(H²) = 0.18 ppm (3-(4-FBz)FT). A similar deshielding effect

was evident in the chemical shifts of H⁷which is locat-

ed ortho- to the carbonyl group in 8-AcFT, 8-BzFT, and

8-(4-FBz)FT. The differences in chemical shift between

these compounds and unsubstituted FT were 0.57, 0.49,

and 0.44 ppm, respectively.

Synthesis

Friedel–Crafts acylations of fluoranthene have previously

been studied. The syntheses of 3-AcFT, 8-AcFT, 3-BzFT, 8-

BzFT, 3,9-Ac₂FT, and 7,10-Ac₂FT are described in the

Struct Chem (2017) 28:511–526

517

Fig. 1 Acetyl-, diacetyl-, benzoyl-, dibenzoyl-, 4-fluorobenzoyl-, and bis(4-fluorobenzoyl)fluoranthenes under study

Molecular and crystal structures

molecular structures are presented in Figs. 2 and 3. Table 3 gives

their crystallographic data. Table 4 gives selected geometrical

parameters derived from the X-ray crystal structures of 8-AcFT,

3,9-Ac₂FT, 3-BzFT, 8-BzFT, and 3-(4-FBz)FT under study.

A characteristic geometric parameter of acylfluoranthene

species is the torsion angle (τ) of the acyl group relative to

the fluoranthene system: C^3a–C³–C¹¹–O¹²for 3-BzFT and

3-(4-FBz)FT, C⁷–C⁸–C¹¹–O¹²for 8-AcFT and 8-BzFT, C^3a–

C³–C¹¹–O¹²and C¹⁰–C⁹–C¹¹–O¹²for 3,9-Ac₂FT, and C^6b–

C⁷–C^11′–O^12′and C^10a–C¹⁰–C¹¹–O¹²for 7,10-Ac₂FT. For

benzoylfluoranthenes, there is also the torsion angle (υ) of

The crystal and molecular structures of the fluoranthene deriva-

tives 8-AcFT, 3,9-Ac₂FT, 7,10-Ac₂FT, 3-BzFT, 8-BzFT, and

3-(4-FBz)FT were determined by X-ray crystallography [40].

Ketones 8-AcFT and 8-BzFT crystallized in the orthorhombic

space group Pbca with C₁symmetry. Ketones 3,9-Ac₂FT, 3-

BzFT, and 3-(4-FBz)FT crystallized in the monoclinic space

groups P2₁/c, P2₁/n, and P2₁/n, respectively with C₁symmetry.

Ketone 7,10-Ac₂FTcrystallized in the orthorhombic space group

P2₁2₁2₁with C₂symmetry. The ORTEP diagrams of their

518

Struct Chem (2017) 28:511–526

519

Table 2 ¹H-, ¹³C-, and ¹⁹F-NMR

chemical shifts (δ, ppm) of mono-

and diacylfluoranthenes in CDCl₃

Peri-H

Ortho-H

¹⁹F-NMR

¹³C-NMR

3-AcFT

8.77 (H⁴)

–

8.86 (H⁴)

8.17 (H²)

8.49 (H⁷)

8.22 (H²)

7.58 (H⁸)

7.85 (H²)

8.41 (H⁷)

7.89 (H²)

7.82 (H²)

8.36 (H⁷)

7.86 (H²)

–

200.4

8-AcFT

7.99 (H⁹)

8.48 (H¹⁰)

7.58 (H⁹)

–

7.86 (H⁹)

7.89 (H⁸)

–

197.9

3,9-Ac₂FT

7,10-Ac₂FT

3-BzFT

8.03 (H⁸)

–

200.3, 197.6

202.13

–

8.17 (H⁴)

–

8.26 (H⁴)

8.10 (H⁴)

–

197.2

8-BzFT

–

196.7

3,9-Bz₂FT

3-(4-FBz)FT

8-(4-FBz)FT

3,9-(4-FBz)₂FT

8.46 (H¹⁰)

–

196.9, 196.5

195.5

–

−105.26

−106.25

−104.73, −105.78

7.82 (H⁹)

8.39 (H¹⁰)

–

195.3

8.21 (H⁴)

7.86(H⁸)

195.2, 194.9

the acyl group relative to the benzene ring C^2′–C^1′–C¹¹–O¹².

In addition, the dihedral angle (θ) between the planes of the

fluoranthene and benzene aromatic systems was defined.

Conformations of the acyl groups are denoted as E when τ is

greater than 90° or as Z when τ is less than 90°.

The carbonyl group in 3-BzFT is tilted out of the planes of the

fluoranthene ring system and the phenyl ring by τ = 28° and 27°,

respectively, with a dihedral angle θ = 58°. 3-BzFT is a slightly

overcrowded isomer; its O^12…H⁴contact distance is 239 pm,

slightly shorter than the sum of the respective Van-der-Waals

radii of hydrogen (115 pm) and oxygen (129 pm) [42].

8-AcFT is considered an essentially planar PAKs with τ = 2°

and θ = 4°. The carbonyl group in 8-BzFT, unlike that in 8-AcFT

is twisted out of the planes of fluoranthene and phenyl moieties

by τ = 23° and υ = 32° with a large dihedral angle θ = 52°.

3,9-Ac₂FT has a large torsion angle of the carbonyl group

at position 3 (τ₃= 22°) and a small torsion angle of the car-

bonyl group at position 9 (τ₉= 3°). In 7,10-Ac₂FT, τ₇= 33°,

and τ₁₀= 32°, the dihedral angles between the acetyl plane and

fluoranthene plane are relatively large: θ₇= 37° and θ₁₀= 38°.

This large titling of the carbonyl groups out of the fluoran-

thene plane is mostly due to the bay regions.

None of the PAKs under study adopts a fully planar con-

formation in their crystal structures. All acylfluoranthenes

crystallize as Z or Z,Z-diastereomers with C₁symmetry. The

values of their carbonyl torsion angles vary. Mono- and

diacylfluoranthenes under study are arranged in the following

order of decreasing torsion angles τ:

were studied at various temperatures and for various periods

of time using PPA as a solvent. The compounds were subject-

ed to PPA at 80–160 °C for 2–6 h. The results of the rear-

1

rangements were characterized by the low-field H-NMR

chemical shifts of the hydrogens ortho and peri to carbonyl

group. The results of the acyl rearrangements of AcFTs versus

BzFTs and Ac₂FT versus Bz₂FT are given in Table 5. Other

rearranged products are excluded. Scheme 1 describes the

Friedel–Crafts acyl rearrangements of AcFTs and 3,9-Ac₂FT.

3-AcFT Friedel–Crafts acyl rearrangements of 3-AcFT in PPA

gave both 3-AcFT and 8-AcFT. The ratio of 8-AcFT increased

considerably by lengthening the time and raising the tempera-

ture of the reaction. FT was also formed upon prolonging the

time of the reaction and raising the temperature.

8-AcFT The reaction of 8-AcFT in PPA at temperatures below

100 °C for varying reaction times did not indicate any acyl

rearrangements or deacetylation. At higher temperatures, 8-

AcFT, in contrast to 3-AcFT, underwent only deacetylation

to give FT. However, during the reactions of both 3-AcFT

and 8-AcFT at temperatures higher than 120 °C, two new

rearrangement products were formed. The first compound I

was separated by PLC, using PE/EtOAc as eluent. Compound

I was tentatively characterized by its ¹H- and ¹³C-NMR spec-

tra. The singlet at δ = 8.47 ppm assigned to H⁷is noted. Also,

the signal at m/z = 431 in the mass spectrum of I is attributed to

an (8-FT)₂C=O⁺¹(C₃₃H₁₈O⁺¹) species. The structure of the

second compound (traces) was not elucidated. A possible

pathway of the formation of bis (8-fluoranthenyl) ketone ((8-

FT)₂C=O) is oxidation and deacetylation of 8-AcFT to give 8-

fluoranthene carboxylic acid (8-FTCO₂H) and FT, respective-

ly, followed by Friedel–Crafts acylaion of FT by 8-FTCO₂H.

7;10−Ac₂FT > 3−BzFT > 3−ð4−FBzÞFT > 8−BzFT

> 3;9−Ac₂FT > 8−AcFT

Friedel–Crafts acyl rearrangements

3,9-Ac₂FT The major rearrangement product of the reactions

of 3,9-Ac₂FT in PPA at high temperatures was 3-methyl-1H-

benzo[cd]fluoranthen-1-one (3-MeBcdFT); 8-AcFT was also

The Friedel–Crafts acyl rearrangements of AcFTs, Ac₂FTs,

BzFTs, 3,9-Bz₂FT, (4-FBz)FTs, and 3,9-(4-FBz)₂FT in PPA

520

Struct Chem (2017) 28:511–526

Fig. 2 ORTEP drawings of the X-ray molecular structures of (Z)-8-AcFT (left), (Z)-8-BzFT (middle), and (Z)-3-BzFT (right)

formed. The structure of the rearrangement product 3-

MeBcdFT was determined by ¹H- and ¹³C-NMR spectra.

The mass spectrum of the rearrangement product of 3,9-

Ac₂FT indicated a C₂₀H₁₂O species (M⁺= 268). The follow-

ing three constitutional isomers were considered: 3-methyl-

1H-benzo[cd]fluoranthen-1-one (3-MeBcdFT), 3-methyl-

1H-cyclopenta[k]fluoranthen-1-one (3-MeCPkFT), and 3-

methyl-1H-cyclopenta[l]fluoranthen-1-one (3-MeCPlFT)

(Fig. 4). The choice of 3-MeBcdFT was based on the NOE

signal between CH₃(2.42 ppm) and H⁴(7.66 ppm). The low-

field doublet at 8.32 ppm representing H¹¹is unlikely to rep-

resent any other hydrogens in the other two constitutional

the low-field doublet of H⁴(not H¹¹) at 8.28 ppm and the four

proton multiplet in the range 7.2–7.7 ppm.

A possible mechanism for the formation of 3-MeBcdFT is

described in Scheme 2: deacetylation of the 9-acetyl group of

3,9-Ac₂FT to give 3-AcFT and acetylium ion, acetylation of

the enol of 3-AcFT, followed by intramolecular Friedel–Crafts

alkylation to give 3-MeBcdFT.

7,10-Ac₂FT This ketone did not undergo any rearrangement

or deacylation in PPA over a wide range of temperatures (60–

160 °C) and for various times of the reactions. The reason for

this lack of reactivity is probably the deactivation effect of the

second acetyl group at position 10 toward deacylation of the

acetyl group at position 7.

1

isomers. The H-NMR chemical shifts of the rearrangement

product are consistent with the reported chemical shifts for

1H–benzo[cd]fluoranthen-1-one (BcdFT) [43] (Fig. 4), e.g.,

Fig. 3 ORTEP drawings of the X-ray molecular structures of (Z)-3-(4-FBz)FT (left), (Z,Z)-3,9-Ac₂FT (middle), and (Z,Z)-7,10-Ac₂FT (right)

Struct Chem (2017) 28:511–526

521

Table 3 Crystallographic data for the acylfluoranthenes under study

8-AcFT

3,9-Ac₂FT

C₂₀H₁₄O₂

3-BzFT

8-BzFT

3-(4-FBz)FT

C₂₃H₁₃FO

7,10-Ac₂FT

C₂₀H₁₄O₂

Empirical

formula

C₁₈H₁₂O

C₂₃H₁₄O

Temperature (K) 295 (1)

173 (1)

Monoclinic

P2₁/c

173 (1)

Monoclinic

P2₁/n

173 (1)

Orthorhombic

Pbca

173 (1)

Monoclinic

P2₁/n

173 (1)

Orthorhombic

P2₁2₁2₁

7.5756 (5)

9.4417 (6)

19.049 (1)

90°

Crystal system

Space group

a (°A)

Orthorhombic

Pbca

13.833 (2)

7.754 (1)

23.805 (4)

90°

11.9313 (6)

7.2530 (4)

17.1787 (8)

90°

4.0946 (2)

29.687 (2)

12.3288 (7)

90°.

7.3362 (5)

18.313 (1)

22.493 (2)

90°

4.0169 (8)

31.132 (6)

12.191 (3)

90°

b (°A)

c (°A)

α (deg)

β (deg)

90°

107.056(1)°

90°

94.236(1)°

90°.

90°

94.410(4)°

90°

γ (deg)

90°

Volume (°A³)

2553.6(7)

8

1421.2(1)

4

1494.6(1)

4

3021.8(3)

8

1520.0(5)

4

1362.5(2)

4

Z

Density (calc.;

Mg/m³)

1.271

1.338

1.361

1.347

1.417

1.396

Reflections

collected

25,808

15,721

17,101

31,211

10,911

15,856

Independent

Reflections

2775

(R_int= 0.0487)

3407

(R_int= 0.0193)

3560

(R_int= 0.0231)

3301

(R_int= 0.0293)

3290

(R_int= 0.0763)

3240

(R_int= 0.0284)

Final R indices

(I > 2σ_I)

R₁= 0.1010,

wR₂= 0.2024

R₁= 0.0495,

wR₂= 0.1290

R₁= 0.0597,

wR₂= 0.1347

R₁= 0.0494,

wR₂= 0.1172

R₁= 0.1478,

wR₂= 0.2912

R₁= 0.0483,

wR₂= 0.1158

3-BzFT The reaction of 3-BzFT in PPA was carried out at

different times and temperatures of the reaction. The rearrange-

ment of 3-BzFTstarted at low temperature, e.g., at 80 °C for 2 h

to give 8-BzFT. At 100 °C for 2 h, the reaction gave 8-BzFT

and 3,9-Bz₂FT in the ratio 26:3. This ratio increased by length-

ening the time and raising the reactions temperature. At 160 °C

for 4 h, the results indicated almost complete debenzoylation of

3-BzFT to FT and rearrangement to 8-BzFT; the ratio was 1 (3-

BzFT): (8-BzFT): 90 (FT).

angle as compared with 3-BzFT, underwent deacylation and

acyl rearrangements more difficultly than 3-BzFT.

The introduction of a fluorine atom at the para positions of

the phenyl group hardly affected the results of rearrangements.

(4-FBz)FTs acted in the same way as BzFTs. The only differ-

ences were the ratios and the temperatures at which the rear-

rangements started.

3-(4-FBz)FT Friedel–Crafts acyl rearrangements of 3-(4-

FBz)FT started at 80 °C to give 8-(4-FBz)FT. At higher tem-

perature, 120 °C for 2 h, 3-(4-FBz)FT, 8-(4-FBz)FT, 3,9-(4-

FBz)₂FT, and FT were formed in the ratios of 41:42:5:12,

respectively. The relative amount of FT increased upon raising

the temperature. At 140 °C for 6 h, 100% of FT was formed.

8-BzFT The reaction of 8-BzFT in PPA at 60–100 °C for 2–

6 h did not give any 3-BzFT. Debenzoylation to FT was ob-

served at temperatures higher than 120 °C. At 160 °C, almost

complete debenzoylation to FToccurred; the ratio 8-BzFT: FT

at 160 °C for 6 h was 7:93.

3,9-Bz₂FT The reaction of 3,9-Bz₂FT in PPA was also stud-

ied. Debenzoylation started at high temperature (140 °C for

4 h) to give 8-BzFT in the ratio 72 (3,9-BzFT): 28 (8-BzFT).

Upon prolonging the reaction time, e.g., 140 °C for 6 h,

debenzoylation to FT also took place. In the acyl rearrange-

ment experiments of 3,9-Bz₂FT, there was no indication for

the formation of rearrangement products, in contrast to 3,9-

Ac₂FT. An aldol condensation is not possible in this case.

The results of Friedel–Crafts acyl rearrangements of 3-

BzFT and 8-BzFT correspond well with the degree of devia-

tion from planarity of the carbonyl group(s). The data given in

Table 5 indicate that 8-BzFT with a relatively small torsion

8-(4-FBz)FT The reaction of 8-(4-FBz)FT in PPA at temper-

atures below 100 °C gave only the starting ketone. At temper-

atures above 120 °C, the deacylation product FT started to

appear. The relative amount of FT increased upon raising the

temperature and prolonging the time of the reactions. At

140 °C for 2 h, 3,9-(4-FBz)₂FT was formed; the ratios were

83 (8-(4-FBz)FT):2 (3,9-(4-FBz)₂FT):15 (FT). At 160 °C for

6 h, the ratio of 8-(4-FBz)FT to FTwas 13:87, whereas 3,9-(4-

FBz)₂FT were not formed. The only difference in behavior

between 8-(4-FBz)FT and 8-BzFT was the formation of

3,9-(4-FBz)₂FT from the former at temperatures higher than

120 °C. Table 6 summarizes the Friedel–Crafts acyl

522

Struct Chem (2017) 28:511–526

Table 4 Selected geometrical

parameters of 3-BzFT, 8-AcFT, 8-

BzFT, 3-(4-FBz)FT, 3,9-Ac₂FT,

and 7,10-Ac₂FT derived from

their X-ray crystal structures

θ (deg)

τ (deg)

υ (deg)

C

_carb–C_arom^a(pm)

O^…H (pm)

CH₃^…H/H^…H (pm)

240.3, H^2….H^2′

(Z)-3-BzFT

C₁57.6

27.7

−146.4

27.4

−149.0

149.1

149.7

239.8, H⁴

253.4, H^6′

(Z)-8-AcFT

C₁4.7

−1.9

–

149.9

249.6, H⁷

262.2, C^13….H⁹

246.6, H^9….H^6′

235.0, H^2….H^2′

176.8

(Z)-8-BzFT

C₁

52.4

22.7

−154.7

31.87

−142.3

149.2

149.8

252.0, H⁷

257.9, H^2′

(Z)-3-(4-FBz)FT

C₁

55.85

−23.54

150.73

−30.14

146.9

149.2

148.8

238.7, H⁴

251.9, H^6′

(Z,Z)-3,9-Ac₂FT

C₁

5.26

24.7

2.7

−178.3

−21.7

155.15

–

149.5

234.7, H⁴

247.5, H¹⁰

259.2, C^13….H²

261.7, C^13′….H⁸

(Z,Z)-7,10-Ac₂FT

C₂

37.2

−33.38

–

150.5

150.2

227.3, H⁶

230.0, H¹

260.9, C^13….H⁹

260.3, C^13′….H⁸

144.4

38.31

32.34

−143.18

^aC³–C¹¹and C^1′–C¹¹for 3-BzFT, C⁸–C¹¹for 8-AcFT, C⁸–C¹¹and C¹–C¹¹for 8-BzFT, C³–C¹¹and C^1′–C¹¹

for 3-BzFT, C³–C¹¹and C⁹–C¹¹for 3,9-Ac₂FT, and C⁷–C¹¹and C¹⁰–C^11′for 7,10-Ac₂FT

rearrangements of BzFTs and Bz₂FT as compared to 4-

FBzFTs and 4-(FBz)₂FT.

8-(4-FBz)FT started to form and its relative amount increased

upon prolonging the time and increasing the temperature. At

140 °C for 4 h the ratios were 53 (3,9-(4-FBz)₂FT):17 (8-(4-

FBz)FT):30 (FT). Treatment of 3,9-(4-FBz)₂FT with

PPA at 120 °C for 6 h gave only (3,9-(4-FBz)₂FT)

and (8-(4-FBz)FT) in the ratio 96:4, respectively. At

3,9-(4-FBz)₂FT No rearrangements were observed when

3,9-(4-FBz)₂FT was treated with PPA at temperatures lower

than 120 °C, 4 h. Upon prolonging the time of the reactions,

Table 5 Products of Friedel–

Starting

material

Temperature

(°C)

Time

(h)

3-XFT

8-XFT

3,9-X₂FT

FT

Crafts acyl rearrangements of

AcFTs, BzFTs, Ac₂FTs, and

Bz₂FTs

X = Ac X = Bz X = Ac X = Bz X = Ac X = Bz

3-AcFT

80

120

100

160

100

160

100

160

80

6

2

4

2

6

2

6

4

6

95

15

−

71

1

5

−

26

9

−

100

66

−

0

3-AcFT

36

−

100

17

−

43

0

3-BzFT

3

3-BzFT

0

90

−

78

−

93

−

8-AcFT

−

100

7

−

100

72

21

8-AcFT

8-BzFT

−

0

3,9-Ac₂FT

3,9-Bz₂FT

−

28

33

100

140

13

−

46

Struct Chem (2017) 28:511–526

523

Scheme 2 Possible pathway of formation of 3-MeBcdFT

the gas phase and in formic acid environment, by plac-

ing the solute in a cavity within the solvent (HCO₂H)

reaction field, using the polarizable continuum model

(PCM) [30]. Recently, a computational model for

predicting the site for electrophilic aromatic substitution

was reported [44, 45]. The model was based on DFT

calculations of the relative stabilities of σ-complex in-

termediate and applied (inter alia) to Lewis-acid-

promoted Friedel–Crafts acylations. AcFTs may adopt

(each) two diastereomeric conformers E and Z; both of

them were considered for non-charged species; in addi-

tion, the methyl group may adopt an eclipsed or a

staggered conformation. O-protonates may adopt anti-

and syn-orientations of the hydroxyl proton. Full confor-

mational search was performed to find the conforma-

tions of σ-complexes arising due to the free rotation

around the sp³C³–C¹¹/C⁸–C¹¹bonds. The results of

the DFT calculations of the acetylfluoranthenes

(AcFTs), their corresponding O-protonates and σ-

complexes in formic acid environment are presented in

Tables 7 and 8 (only the global minima conformations

are shown; see Electronic supplementary material for

the complete data).

Scheme 1. Friedel–Crafts acyl rearrangements of AcFTs and 3,9-Ac₂FT

140 °C for 6 h, the reaction gave 3,9-(4-FBz)₂FT and

8-(4-FBz)FT in the ratio 41:59, respectively.

DFT study

3- and 8-Acetylfluoranthenes (3-AcFT and 8-AcFT),

3,8- and 3,9-diacetylfluoranthenes (3,8-Ac₂FT and 3,9-

Ac₂FT), and their derivatives which may be involved

in their Friedel–Crafts acyl rearrangements, were sub-

jected to a systematic DFT study. Calculations at

B3LYP/6-31G(d) were carried out for the species in

According to the results of the DFT calculations,

acetylfluoranthenes 3-AcFT, 8-AcFT, and O-protonate

3-AcFTH⁺adopt the Z conformations as their global

minima. 8-AcFT adopts the Z conformation also in the

X-rays structure (vide supra). The global minimum (E)-

8-AcFTH⁺is only 1.2 kJ/mol higher in energy than its

Z-diastereomer. In the series of diacetylfluoranthenes,

(Z,E)-3,8-Ac₂FT and (Z,Z)-3,9-Ac₂FTH⁺are the global

minima conformations, with (Z,Z)-3,8-Ac₂FTH⁺only

0.4 kJ/mol higher in energy than (Z,E)-3,8-Ac₂FT. The

gas phase calculations gave Z-diastereomers of 8-

AcFTH⁺and (Z,Z)-3,8-Ac₂FTH⁺as the respective global

Fig. 4 Polycyclic aromatic ketones related to the acyl rearrangement of

3,9-Ac₂FT

524

Struct Chem (2017) 28:511–526

Table 6 Products of Friedel–Crafts acyl rearrangements of BzFTs, Bz₂FT, 4-FBzFTs, and 4-(FBz)₂FT

Starting material

Temperature (°C)

Time (h)

3-XFT

X = Bz

8-XFT

X = Bz

3,9-X₂FT

X = Bz

FT

X = 4-FBz

3-BzFT

100

160

80

2

4

2

4

2

6

4

2

6

4

71

1

−

100

41

30

−

26

9

−

3

−

0

3-BzFT

0

90

−

12

54

−

93

−

15

62

87

−

3-(4-FBz)FT

8-BzFT

−

0

−

100

7

0

−

0

120

140

100

160

80

42

15

−

5

0

−

8-BzFT

0

−

0

−

0

8-(4-FBz)FT

3,9-Bz₂FT

3,9-(4-FBz)₂FT

−

0

−

100

83

36

13

−

100

21

−

0

140

160

100

140

100

140

0

2

0

2

0

−

0

−

0

33

−

0

46

−

0

100

0

17

−

53

30

minima conformations. These results show the prefer-

ence of Z conformations of an acyl substituent in posi-

tion 3 of the fluoranthene system, and no distinct pref-

erence of either Z- or E-conformations of an acyl sub-

stituent in the 8/9 positions. Only Z-conformations were

further considered for the O-protonates and σ-complexes

of diacetylfluoranthenes.

The proposed mechanism of the Friedel–Crafts acyl rear-

rangements of acetylfluoranthenes in PPA (Scheme 3) in-

volves deacetylation of 3-AcFT to FT and acetylium ion Ac⁺

via the protonate 3-AcFTH⁺and the σ-complex 3σ-AcFTH⁺,

followed by acetylation at the 8-position to give 8-AcFT via

the σ-complex 8σ-AcFTH⁺and the protonate 8-AcFTH⁺.

According to the Hammond–Leffler postulate [46], the rel-

ative energies of the transitions states for the formation of the

σ-complexes, resemble the relative energies of the σ-com-

plexes. In the case of mono-acetylfluoranthenes, both the ke-

tone 8-AcFT and the O-protonate 8-AcFTH⁺are lower in

relative energies than their respective 3-substituted constitu-

tional isomers (Tables 7 and 8). However, the energy barrier

The following relative stabilities of the constitutional

isomers of acetylfluoranthenes and their derivatives are

(i) ketones: ΔG₂₉₈= 0.0 kJ/mol ((Z)-8-AcFT) and

11.3 kJ/mol ((Z)-3-AcFT); (ii) O-protonates:

ΔG₂₉₈= 0.0 kJ/mol ((Z)-8-AcFTH⁺) and 14.71 kJ/mol

( ( Z ) - 3 - A c F T H ⁺) ; a n d ( i i i ) σ - c o m p l e x e s :

ΔΔG₂₉₈= 0.0 kJ/mol (3σ-AcFTH⁺) and 4.4 kJ/mol

(8σ-AcFTH⁺). The relative stabilities of the constitution-

al isomers of diacetylfluoranthenes are ketones:

ΔG₂₉₈= 0.0 kJ/mol ((Z,E)-3,8-Ac₂FT), 0.9 kJ/mol

((Z,Z)-3,9-Ac₂FT) (however, in the gas phase

ΔG₂₉₈= 0.0 kJ/mol ((Z,Z)-3,9-Ac₂FT), and 0.8 kJ/mol

( ( Z , Z ) - 3 , 8 - A c ₂F T ) ) ; ( i i ) O - 3 - p r o t o n a t e s :

ΔΔG₂₉₈= 0.0 kJ/mol ((Z,Z)-3,9-Ac₂FTH⁺) and 4.1 kJ/

mol ((Z,Z)-3,8-Ac₂FTH⁺); (iii) O-8/9-protonates:

ΔG₂₉₈= 0.0 kJ/mol ((Z,Z)-3,9-Ac₂FTH⁺) and 3.4 kJ/

mol ((Z,Z)-3,8-Ac₂FTH⁺); (iv) di-O-protonates:

ΔG₂₉₈= 0.0 kJ/mol ((Z,Z)-3,9-Ac₂FTH₂⁺⁺) and

10.9 kJ/mol ((Z,Z)-3,8-Ac₂FTH₂⁺⁺); (v) σ-complexes:

ΔG₂₉₈= 0.0 kJ/mol (3,9σ-Ac₂FTH⁺) and 6.4 kJ/mol

(3,8σ-Ac₂FTH⁺); (v) O-protonated σ-complexes:

ΔΔG₂₉₈= 0.0 kJ/mol (3,9σ-Ac₂FTH₂⁺⁺) and 18.4 kJ/

mol (3,8σ-Ac₂FTH₂⁺⁺).

Table 7 Relative Gibbs-free energies of acetylfluoranthenes and their

torsion angles (τ)

ΔG₂₉₈(kJ/mol)

τ (deg)

(Z)-3-AcFT

C_s

C₁

C_s

C₁

C_s

C₁

11.25

21.17

0.00

0

158

0

(E)-3-AcFT

(Z)-8-AcFT

(E)-8-AcFT

0.85

180

0

(Z)-3-AcFTH⁺

(E)-3-AcFTH⁺

(Z)-8-AcFTH⁺

(E)-8-AcFTH⁺

3σ-AcFTH⁺

8σ-AcFTH⁺

14.71

24.49

1.24

169

0

0.00

180

−85

−177

74.02

78.37

Struct Chem (2017) 28:511–526

525

Table 8 Relative Gibbs-free energies of diacetylfluoranthenes and their

torsion angles (τ)

FT (in addition to the rearrangement product 3-MeBcdFT),

whereas 3-AcFT was not identified among the products.

In the cases of diacetylfluoranthenes, ketones (Z,E)-

3,8-Ac₂FT and (Z,Z)-3,9-Ac₂FT have very similar rela-

tive energies, whereas 3,9-disubstituted O-protonates and

σ-complexes have lower relative energies than their re-

spective 3,8-disubstituted constitutional isomers

(Tables 7 and 8). The lower relative energies of 3,9-

disubstituted diacetylfluoranthenes as compared to 3,8-

disubstituted diacetylfluoranthenes are even more pro-

nounced for the di-O-protonates and for the mono-O-

protonated σ-complexes. The experimental results of

the AlCl₃-mediated Friedel–Crafts acetylation of

acetylfluoranthenes demonstrated that both 3-AcFT and

8-AcFT yield only 3,9-Ac₂FT. Thus, both kinetic control

and thermodynamic control of the Friedel–Crafts acety-

lations of 3-AcFT and 8-AcFT favor the formation of

the constitutional isomer 3,9-Ac₂FT.

ΔG₂₉₈(kJ/mol) τ₃(deg) τ₈/τ₉(deg)

(Z,Z)-3,8-Ac₂FT

C_s

C₁

C_s

C₁

C_s

C₁

0.41

0.00

0.90

1.54

6.15

2.03

3.36

0.00

89.88

83.46

10.89

0.00

0

180

0

(Z,E)-3,8-Ac₂FT

(Z,Z)-3,9-Ac₂FT

0

(Z,E)-3,9-Ac₂FT

0

180

0

(Z,Z)-3H,8-Ac₂FTH⁺

(Z,Z)-3H,9-Ac₂FTH⁺

(Z,Z)-3,8H–Ac₂FTH⁺

(Z,Z)-3,9H–Ac₂FTH⁺

(Z)-3,8σ-Ac₂FTH⁺

(Z)-3,9σ-Ac₂FTH⁺

2

0

18

−1

2

−178

168

0

++

(Z,Z)-3,8-Ac₂FTH₂

++

(Z,Z)-3,9-Ac₂FTH₂

2

0

++

(Z)-3H,8σ-Ac₂FTH₂

(Z)-3H,9σ-Ac₂FTH₂

C₁117.38

C₁99.00

5

177

172

++

−3

for the formation of the σ-complex 3σ-AcFTH⁺is lower than

the respective energy barrier leading to 8σ-AcFTH⁺. The ex-

perimental results of the PPA-mediated Friedel–Crafts acyl

rearrangements of acetylfluoranthenes demonstrated that 3-

AcFT undergoes transformation into 8-AcFT and 3-BzFT

gives 8-BzFT, but both 8-AcFTand 8-BzFTyield only FTunder

the same conditions. Thus, the Friedel–Crafts acyl rearrange-

ments 3-AcFT → 8-AcFT and 3-BzFT → 8-BzFT are thermo-

dynamically controlled processes. Accordingly, 3-AcFT is the

kinetically-controlled product, whereas 8-AcFT is the

thermodynamically-controlled product. Consistently, deacylation

of 3,9-Ac₂FT in PPA gave the more stable isomer 8-AcFT and

Conclusions

Friedel–Crafts acetylation and benzoylation of fluoranthene

gave 3-, 8-, and 3, 9-acetyl, benzoyl and 4-

fluorobenzoylfluoranthene. Friedel–Crafts mono- and

diacylation of FT and of acylfluoranthenes and Friedel–

Crafts acyl rearrangements of acylfluoranthenes and

diacylfluoranthene in PPA proved to be regioselective.

Noteworthy is the regioselectivity of acylation of 3-

acylfluoranthenes to give 3,9-diacylfluoranthenes, not

3,8-acylfluoranthenes. The acyl rearrangements of

monoacylfluoranthenes were not reversible: the kinetically

controlled 3-AcFT/3-BzFT rearranged to the thermodynami-

cally controlled 8-AcFT/8-BzFT, whereas the latter did not

rearrange to the former. The values of the carbonyl torsion

angles of mono- and diacylfluoranthenes derived from the

X-ray study, correspond well with their ability to undergo

Friedel–Crafts acyl rearrangements. The order of decreasing

torsion angles between the carbonyl and the fluoranthene ring

system τ is: 7,10-Ac₂FT > 3-BzFT > 3-(4-FBz)FT > 8-

BzFT > 3,9-Ac₂FT > 8-AcFT. The regioselectivity and the

win of kinetic control over thermodynamic control were sup-

ported by the results of the DFT calculations. Furthermore,

3,9-Ac₂FT, 3,9-Bz₂FT, and 3,9-(4-FBz)₂FT underwent

deacylation in PPA to give 8-AcFT, 8-BzFT, and 8-(4-

FBz)FT, respectively. 3-Acylfluoranthenes were not isolated

among the acyl rearrangement products of 3,9-

diacylfluoranthenes. However, the deacetylation of 3,9-

Ac₂FT in PPA gave also the rearrangement product 3-

MeBcdFT, indicating the formation of 3-AcFT as an interme-

diate, which then underwent an aldol condensation followed

by a Friedel–Crafts cyclization and dehydration. The rich

Friedel–Crafts chemistry in PPA in the fluoranthene series is

Scheme 3 Possible mechanisms of 3-AcFT → 8-AcFT acyl

rearrangement

526

Struct Chem (2017) 28:511–526

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26. SHELXTL-NT V6.1, BRUKER AXS GMBH, D-76181 (2002)

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Article Doi

Friedel–Crafts acyl rearrangements in the fluoranthene series

DOI: 10.1007/s11224-016-0894-7

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Full text of DOI:10.1007/s11224-016-0894-7

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