New strong base synthesis of symmetrical 1,5-diaryl-1,3,5-pentanetriones from acetone and benzoate esters

Article abstract of DOI:10.1080/00397910802138488

Lithium hexamethyldisilazide (LiHMDS) was used to condense substituted benzoate esters with acetone to afford symmetrical 1,5-diaryl-1,3,5- pentanetriones that were isolated, characterized (including a representative X-ray crystallographic analysis), and

Full text of DOI:10.1080/00397910802138488

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New Strong Base Synthesis of
Symmetrical 1,5-Diaryl-1,3,5-
pentanetriones from Acetone
and Benzoate Esters
John D. Knight a , Clyde R. Metz a , Charles F. Beam a
, William T. Pennington b & Donald G. VanDerveer b
a Department of Chemistry and Biochemistry,
College of Charleston, Charleston, South Carolina,
USA
b Department of Chemistry, Clemson University,
Clemson, South Carolina, USA
Version of record first published: 11 Jul 2008.
To cite this article: John D. Knight , Clyde R. Metz , Charles F. Beam , William T.
Pennington & Donald G. VanDerveer (2008): New Strong Base Synthesis of Symmetrical
1,5-Diaryl-1,3,5-pentanetriones from Acetone and Benzoate Esters, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 38:14, 2465-2482
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Synthetic Communications1, 38: 2465–2482, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802138488
New Strong Base Synthesis of Symmetrical
1,5-Diaryl-1,3,5-pentanetriones from Acetone
and Benzoate Esters
John D. Knight,1 Clyde R. Metz,1 Charles F. Beam,1
William T. Pennington,2 and Donald G. VanDerveer2
1Department of Chemistry and Biochemistry, College of Charleston,
Charleston, South Carolina, USA
2Department of Chemistry, Clemson University, Clemson,
South Carolina, USA
Abstract: Lithium hexamethyldisilazide (LiHMDS) was used to condense
substituted benzoate esters with acetone to afford symmetrical 1,5-diaryl-1,3,5-
pentanetriones that were isolated, characterized (including a representative X-ray
crystallographic analysis), and acid cyclized to the respective 2,6-diaryl-4H-
pyran-4-ones.
Keywords: Acetone; benzoate esters; diarylpentanetriones; lithium hexamethyldi-
silazide
INTRODUCTION
One of the earliest methods for the preparation of 1,5-diaryl-1,3,5-
pentanetriones, developed by Hauser et al. involved the condensation of
1-benzoylacetone with ethyl benzoate employing potassium amide in liquid
ammonia[1] or sodium hydride in monoglyme.[2] They also reported sodium
hydride initiated condensations of acetone 1 with several benzoate esters 2
to afford symmetrical 1,5-diaryl-1,3,5-pentanetriones 3. Also, diphenyl tri-
ketone 3a has been prepared by hydrolysis opening of 2,6-diphenylpyran-
4-one with either potassium hydroxide or potassium methoxide.[3]
Received in the USA March 23, 2008
Address correspondence to Charles F. Beam (synthesis) or Clyde R. Metz
(X-ray), Chemistry and Biochemistry, College of Charleston, Charleston, SC
29424, USA. E-mail: beamc@cofc.edu or metzc@cofc.edu
2465

2466
J. D. Knight et al.
A
few symmetrical 1,5-diaryl-1,3,5-pentanetriones have been
reported since the initial reports,[4] indicating the potential for them to
be used in the preparation of useful heterocyclic compounds,[5] chelates,[6]
and other compounds,[7] many of which have biological potential.[8]
Also, 1,3-diaryl-1,3,5-pentanetriones have been involved in spectral,
theoretical, and X-ray studies.[9]
Our initial focus was on the possible substitution of lithium
hexamethyldisilazide (LiHMDS) or lithium diisopropylamide (LDA) in
tetrahydrofuran (THF) for sodium hydride in the preparation of substi-
tuted 1-aroylacetones and 1,5-diarylpentanetriones. Syntheses of these
di- and triketones by an alternative new method offer an expanded
potential for some of the various studies cited.
RESULTS AND DISCUSSION
During the current investigation, monolithiated acetone 10 was prepared
from acetone 1 by deprotonation with either excess LiHMDS or LDA
and was condensed with a variety of substituted benzoate esters 2
(Scheme 1). Initially, LiHMDS was used for lithiation of 1 followed
by condensation with methyl 3,4,5-trimethoxybenzoate, and this
resulted in 1,3-diacylation of 1 to afford symmetrical 1,5-bis(3,4,5-
trimethoxyphenyl)-1,3,5-pentanetrione 3d (1:2 condensation acetone–
ester) in 68% yield. The general ratio of reactants was determined for this
reaction and the other reaction products (acetone–LiHMDS–ester 1:3:2);
see Table 1.
Scheme 1. 1,5-Diaryl-1,3,5-pentanetriones 3a–i and 2,6-diaryl-4H-pyran-4-
ones 4a–i.

2467

2468
J. D. Knight et al.
Triones 3a, 3b, and 3h from this group of symmetrical triones 3a–i,
reported here have been cited previously.[1,2] In this study, 3a–i were iso-
lated in 41–78% yield, with an average 62% yield. Each of these triones
was acid cyclized to the targeted pyranone 4a–i in 71–84% yield, with an
average yield of 80%; pyranones 4d–f are new.
The 1:1 condensation of lithiated acetone 10, from LDA deprotona-
tion of 1, with methyl 3,4,5-trimethoxybenzoate occurred [acetone–
LDA–ester 1:3:1] to afford 1-(3,4,5-trimethoxyphenyl)-1,3-butanedione
in 65% yield[10]; however, this is a limited synthesis currently under
separate investigation.
All compounds were characterized by absorption spectra with sup-
port from combustion analysis when applicable. IR spectra displayed car-
bonyl and other absorptions for triones 3, 1568–1600 cmꢁ1and 1635–
1669 cmꢁ1 for pyranones 4; 13C and 1H NMR spectra for 3a–i displayed
numerous additional absorptions that indicated the presence of several
tautomers in solution. Although this has resulted in complex absorption
spectra,[4d,7c,9] 1H NMR of each product 3a–i, displayed two separate
methylene proton absorptions and two separate methyne proton absorp-
tions. The range for the two methylene protons was d 3.99–4.51 ppm with
an average of d 4.22 ppm, and the second methylene was d 4.15–4.65 ppm
with an average of d 4.39 ppm. Methyne protons were noted from d 5.99
to 6.65 ppm, average of d 6.27 ppm. The second methyne proton was
d 6.23–6.86 ppm, with an average of d 6.52 ppm. NMR spectra for 4a–i
were straightforward, with characteristic 1H NMR for C3-H d 6.70–
6.99 ppm and 13C NMR for carbonyl carbons from d 178.2–180.8 ppm.
As a result of obtaining good quality crystals for 3d, an X-ray single-
crystal analysis of trione 3d was completed. Analysis of the data indicated
a single tautomer in the crystal. The molecular structure is shown in
Figures 1 and 2 and selected bond distances and angles are listed in
Table 2. Atomic positional parameters and all bond distances and angles
Figure 1. ORTEP[14] diagram (50% ellipsoid for non hydrogen atoms) for 3d,
C23H26O9.

1,5-Diaryl-1,3,5-pentanetriones
2469
Figure 2. Conventional illustration of 3d.
are listed in the supplementary material. CCDC 657942 contains the sup-
plemental crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
The molecule exhibits both intramolecular and intermolecular hydro-
gen bonding. The O1 atom is bonded to the H atoms bonded to O2 and
O6 within the same molecule, and the O1 atom is bonded to the H atom
bonded to O2 in another molecule.
When other bases such as LDA, lithium 2,6-dimethylpiperidide, or
lithium diethylamide were used, diaryl triones 3a–i did not result, and this
indicates that the reaction itself is dependent on the overall properties of
LiHMDS as a base. The ratio of acetone and LiHMDS is important.[15]
.
Optimum yields were obtained when the ratio was 1:3:2 (acetone–
LiHMDS–ester), and essentially no product was obtained with a ratio
of 1:2:2 (acetone–LiHMDS–ester). This is compared to ratios used with
sodium hydride–activated synthesis: 1:5:3 (acetone–NaH–ester).[2]
Although this is a synthesis report, it opens the possibility of further
studies. One of three intermediates may be involved: the 1,3-dianion of
acetone 100; the 1,3-dianion of 1-aroylacetone 500; and a monoanion of
1-aroylacetone 50. The participation of 100 in this reaction is improbable,
because its preparation requires the sequential reactions of two stronger
bases under different reaction conditions.[16] Arguments can be made for
and against 500 or 50 based on the strength of base, coordination ability,
and size of LiHMDS. Additional mechanistic studies would be required
to confirm or deny either of these intermediates. See Fig. 3.
CONCLUSIONS
A new synthesis of 1,5-diaryl-1,3,5-pentanetriones 3a–i and their acid
cyclization to 1,6-diarylpyranones 4a–i has resulted in an experimental
sequence for the preparation of multigram quantities of targeted

2470
J. D. Knight et al.
Figure 3. Reaction intermediates.
products that can easily be purified by recrystallization from common
solvents. Because all procedures are general, the yield of a particular pro-
duct may not be optimal, and the preparation of individual compounds
has potential for being scaled up. The synthetic processes are practical
in terms of the availability of acetone, benzoate esters, and reagents.
Our explanation for the exclusivity of LiHMDS over other lithium bases
is incomplete based on this initial investigation, but strength and size of
base in comparison to other lithium bases, along with the lithium nitro-
gen coordination ability of hexamethyldisilazine, need to be taken into
account. The project data has also provided results for spectral, X-ray,
and theoretical studies.
EXPERIMENTAL
Melting points were obtained with a Mel-Temp II melting-point appar-
atus in open capillary tubes and are uncorrected. Fourier Transform
infrared spectra were obtained with a Nicolet Impact 410 FT-IR and a
Mattson Genesis II FT-IR with Specac Golden Gate Accessory. Nuclear
magnetic resonance (NMR) spectra were obtained with a Varian
Mercury-Vx spectrometer in an Oxford 300=54 magnet. Chemical shifts
are recorded in d parts per million (ppm) downfield from internal tetra-
methylsilane (TMS) reference. Combustion analyses were performed by
Quantitative Technologies, Inc., Whitehouse, N.J.
X-ray Determination
Single-crystal X-ray measurements for crystals of 3d C23H26O9 recrystal-
lized from benzene were collected on a Mercury CCD area detector

1,5-Diaryl-1,3,5-pentanetriones
2471
coupled with a Rigaku AFC8 diffractometer with graphite mono-
˚
chromated Mo-Ka (k ¼ 0.71073A) radiation. The data were collected
at a temperature of 163(2) K to a maximum h value of 25.14ꢀ. Data were
collected in 0.50ꢀoscillations in x (two identical scans were performed
at each position to identify detector anomalies). A sweep of data was
done using x oscillations from ꢁ90.0 to 90.0ꢀ at v ¼ 45.0ꢀ and
/ ¼ 0.0ꢀ; a second sweep was performed using x oscillations from
ꢁ30.0 to 30.0ꢀat v ¼ 45.0ꢀ and / ¼ 90.0ꢀ. Data were collected, pro-
cessed, and corrected for Lorentz polarization and for absorption
using CrystalClear (Rigaku).[17] Cell parameters and additional details
of the data collection are reported in Table 3 and in the supplementary
material.
The structure was solved by direct methods and expanded using
Fourier techniques. Structure solution, refinement, and the calculation
of derived results were performed using the SHELX-97[18] package of
computer programs. Neutral atom scattering factors were those of
Cromer and Waber,[19] and the real and imaginary anomalous dispersion
corrections were those of Cromer.[20]
The nonhydrogen atoms were refined anisotropically. Ideal hydrogen
atom coordinates were calculated, and the hydrogen atoms were allowed
to ride on their respective carbons atoms. The hydrogen atoms on O2 and
O6 were located from a difference Fourier and the coordinates were
fixed. The temperature factors of all hydrogen atoms were varied isotro-
pically. The final cycle of full-matrix least-squares refinement were
performed on F2.
ꢀ
˚
Table 2. Selected bond distances (A) and angles ( )
Parameter
Value
C1–C2
C1–C10
C2–C3
C10–C11
C3–C4
C11–C12
C1–O1
C3–O2
C11–O6
C4–C5
C5–C6
1.429(3)
1.437(3)
1.354(3)
1.357(3)
1.475(3)
1.478(3)
1.277(2)
1.335(2)
1.338(2)
1.402(3)
1.385(3)
(Continued)

2472
J. D. Knight et al.
Table 2. Continued
Parameter
Value
C6–C7
C7–C8
C8–C9
C9–C4
C12–C13
C13–C14
C14–C15
C15–C16
C16–C17
C17–C12
C6–O3
C7–O4
C8–O5
C14–O7
C15–O8
C16–O9
O3–C18
O4–C19
O5–C20
1.404(3)
1.389(3)
1.388(3)
1.396(3)
1.395(3)
1.389(3)
1.400(3)
1.389(3)
1.391(3)
1.397(3)
1.368(2)
1.379(2)
1.368(2)
1.365(2)
1.378(2)
1.365(3)
1.435(3)
1.425(3)
1.424(3)
1.428(3)
1.421(3)
1.396(3)
119.3(2)
123.1(2)
122.9(2)
125.0(2)
123.2(2)
120.4(2)
119.5(2)
117.2(2)
116.1(2)
114.0(2)
114.0(2)
117.5(2)
118.4(2)
120.6(2)
120.1(2)
121.1(2)
121.8(2)
113.9(2)
114.9(2)
O7–C21
O8–C22
O9–C23
C10–C1–C2
C1–C2–C3
C1–C10–C11
C2–C3–C4
C10–C11–C12
C3–C4–C5
C11–C12–C13
C6–O3–C18
C14–O7–C21
C7–O4–C19
C15–O8–C22
C8–O5–C20
C16–O9–C23
O1–C1–C2
O1–C1–C10
O2–C3–C2
O6–C11–C10
O2–C3–C4
O6–C11–C12

1,5-Diaryl-1,3,5-pentanetriones
2473
Table 3. Selected crystallographic data, 3d, C23H26O9, CCDC 657942
Parameter
Value
Crystal dimensions (mm)
Space group
0.65 ꢂ 0.46 ꢂ 0.24
P2(1)=n
8.188 (2)
26.706 (5)
10.184 (2)
90ꢀ
˚
a (A)
˚
b (A)
˚
c (A)
a
b
100.75 (3)ꢀ
90ꢀ
c
Limiting indices
ꢁ9 ꢃ h ꢃ 9
ꢁ25 ꢃ k ꢃ 31
ꢁ12 ꢃ l ꢃ 12
2188.0 (7)
446.44
3
˚
V (A )
fw
Z
4
1.355
0.105
15
37.95
12514
3811
0.0301
0.0514
0.1283
1.078
0.167
dcalc (g=cm3)
l (mmꢁ1
)
Exposure time (s)
Crystal-to-detector distance (mm)
Number of reflections
Unique reflections
Rint
R1 (I > (2.00)r(I))a
wR2 (all data)b
Goodness of fit
ꢁ3
˚
Highest differenceꢁp3eak (e A
)
˚
Deepest hole (e A
)
ꢁ 0.278
aR1 ¼ RðjFoj ꢁ jFcjÞ=RjFoj
2
2
1=2
bwR2 ¼ fR½wðFo2 ꢁ Fc2Þ ꢄ=R½wðFo2Þ ꢄg
General Procedure for Preparation of 1,5-Diaryl-1,3,5-
pentanetriones (3a–i)
[Ratio of reagents acetone–LiHMDS–ester 1:3:2]. A 20.0 mL sample of
1.6 M n-butyllithium (0.0315 mol) in hexanes (0 ꢀC) under N2 was added
to a three-necked round-bottomed flask (e.g., 500 mL), equipped with a
nitrogen inlet tube, a side-arm addition funnel (e.g., 125 mL), and a
magnetic stir bar. The flask was cooled in an ice-water bath, and 5.24 g
(0.0315 mol) of hexamethyldisilazine (97%, Aldrich Chem. Co.) dissolved
in 25–30 mL of dry THF (freshly distilled from sodium) was added from

2474
J. D. Knight et al.
the addition funnel at a fast drop rate during a 5-min (0ꢀ, N2) period. The
solution was stirred for an additional 15–20 min and then treated via the
addition funnel, during 5 min, with 0.581 g (0.0100 mol) of distilled
acetone dissolved in 30 mL of THF. After 10–15 min, 2 equivalents
(0.0210 mol þ 5% excess) of an aromatic ester dissolved in 25 mL of
THF were added, and the solution was allowed to stir overnight under
N2 atmosphere and at room temperature. Finally, 100 mL of 3 M
hydrochloric acid was added all at once. The two-phase mixture was well
stirred for 5 min. It was then poured into a large flask (ca. 1 or 2 L)
containing ice (ca. 100 g), followed by the addition of 100 mL of sol-
vent-grade ether. The mixture was then neutralized with solid sodium
bicarbonate, and the layers were separated. The aqueous layer was extracted
with ether (2 ꢂ 50 mL), and the organic fractions were combined, not dried,
and evaporated. Most products crystallized upon removal of the organic sol-
vents. Recrystallization was achieved using common solvents such as etha-
nol, benzene=ethanol, benzene=hexanes, or hexanes.
Data
1,5-Diphenyl-1,3,5-pentanetrione (3a)
Acetone was condensed with methyl benzoate (1:2) using the general pro-
cedure to afford 1.68 g of 3a, dark gold-colored crystals. IR: 1586 cmꢁ1
.
1H NMR (CDCl3): d 4.29 (s), 4.44 (s), 6.34 (s), 6.61 (s), 7.47–7.65 (m),
and 7.87–8.04 (m). 13C NMR (CDCl3): d 50.2, 54.0, 97.6, 98.4, 126.8,
127.5, 129.0, 129.3, 132.5, 133.3, 133.6, 134.3, 136.7, 173.4, 182.0,
192.5, 194.6, and 194.7.
1,5-bis(4-Methoxyphenyl)-1,3,5-pentanetrione (3b)
Acetone was condensed with methyl 4-methoxybenzoate (1:2) using the
general procedure to afford 2.55 g of 3b, yellow crystals. IR:
1
1584 cmꢁ1. H NMR (CDCl3): d 3.83–3.84 (m), 4.14 (s), 4.30 (s), 6.24
(s), 6.48 (s), 7.00–7.04 (m), and 7.81–7.98 (m). 13C NMR (CDCl3):
d 49.2, 53.9, 56.2, 56.3, 96.3, 97.8, 114.6, 114.7, 115.0, 125.7, 126.8,
128.9, 129.8, 129.9, 131.6, 163.1, 163.8, 164.2, 173.0, 183.3, 190.5,
193.5, 193.8, and 194.0.
1,5-bis(3,4-Dimethoxyphenyl)-1,3,5-pentanetrione (3c)
Acetone was condensed with methyl 3,4-dimethoxybenzoate (1:2) using
the general procedure to afford 2.27 g of 3c, bright yellow crystals. IR:

1,5-Diaryl-1,3,5-pentanetriones
2475
1584 cmꢁ1. 1H NMR (CDCl3): d 3.93–3.95 (m), 4.04 (s), 4.28 (s), 5.94 (s),
6.26 (s), 6.86–6.92 (m), and 7.36–7.71 (m). 13C NMR (CDCl3) d (ppm):
50.3, 56.2, 56.3, 95.9, 96.5, 109.2, 109.8, 110.3, 110.4, 110.7, 112.2,
120.4, 121.6, 124.4, 126.6, 127.1, 129.7, 149.1, 149.2, 152.3, 153.2,
154.1, 173.5, 183.4, 188.8, 192.7, and 193.3. Anal. calcd. for
C21H22O7ꢅ1=2 H2O: C, 63.79; H, 5.86. Found: C, 63.74; H, 5.86.
1,5-bis(3,4,5-Trimethoxyphenyl)-1,3,5-pentanetrione (3d)
Acetone was condensed with methyl 3,4,5-trimethoxybenzoate (1:2) using
the general procedure to afford 3.08 g of 3d, golden crystals. IR:
1
1589 cmꢁ1. H NMR (CDCl3): d 3.90 (s), 3.91–3.93 (m), 4.08 (s), 5.96
(s), 6.23 (s), 7.08 (s), 7.10 (s), and 7.32 (s). 13C NMR (CDCl3): d 50.5,
55.9, 56.0, 60.7, 96.1, 96.5, 103.4, 104.2, 128.6, 128.9, 131.0, 141.0,
142.0, 152.8, 152.9, 173.1, 189.2, 192.2, and 193.0. Anal. calcd. for
C23H26O9: C, 61.88; H, 5.87. Found: C, 61.90; H, 5.88.
1,5-bis(3,5-Dimethoxyphenyl)-1,3,5-pentanetrione (3e)
Acetone was condensed with methyl 3,5-dimethoxybenzoate (1:2)
using the general procedure to afford 2.35 g of 3e, bright yellow crystals.
1
IR: 1568 cmꢁ1. H NMR (DMSO-d6): d 3.80–3.81 (m), 4.31 (s), 4.43
(s), 6.50 (s), 6.71–6.80 (m), and 7.00–7.13 (m). 13C NMR (DMSO-d6):
d 49.6, 55.5, 55.6, 97.7, 98.5, 104.1, 104.2, 104.7, 104.9, 105.5,
106.3, 135.0, 135.8, 138.1, 160.7, 160.7, 172.3, 181.2, 191.9, 193.9, and
194.1. Anal. calcd. for C21H22O7: C, 65.28; H, 5.74. Found: C, 65.12;
H, 5.65.
1,5-bis(4-Fluorophenyl)-1,3,5-pentanetrione (3f)
Acetone was condensed with methyl 4-fluorobenzoate (1:2) using
the general procedure to afford 1.78 g of 3f, faint yellow crystals.
.
IR: 1589 cmꢁ1 1H NMR (DMSO-d6): d 4.32 (s), 4.46 (s), 6.41 (s),
6.70 (s), 7.31–7.40 (m), and 7.90–8.12 (m). 13C NMR (DMSO-d6):
d 49.2, 53.4, 97.0, 98.0, 115.7, 115.8, 115.9, 116.1, 116.2, 128.9,
129.0, 129.4, 129.8, 129.9, 130.3, 131.5, 131.6, 132.9, 162.8, 163.3,
163.7, 166.1, 166.6, 167.1, 171.6, 180.9, 191.3, 193.1, 193.7, 193.8,
and 201.4. 19F NMR (DMSO-d6): d ꢁ107.77-(ꢁ)107.68(m),ꢁ106.66-
(ꢁ)106.56(m), ꢁ105.63-(ꢁ)105.53(m), and ꢁ105.50-(ꢁ)105.40 (m).
Anal. calcd. for C17H12F2O7: C, 67.55; H, 4.00. Found: C, 67.23;
H, 3.85.

2476
J. D. Knight et al.
1,5-bis(4-Chlorophenyl)-1,3,5-pentanetrione (3g)
Acetone was condensed with methyl 4-chlorobenzoate (1:2) using the
general procedure to afford 2.01 g of 3g, light yellow crystals. IR:
ꢀ
1
1588 cmꢁ1. H NMR (DMSO-d6 at 90 C): d 4.30 (s), 4.40 (s), 6.41 (s),
6.61 (s), 7.55–7.58 (m), and 7.87–8.01 (m). 13C NMR (DMSO-d6 at
90 ꢀC): d 50.2, 54.1, 98.3, 98.9, 128.8, 129.4, 129.6, 129.7, 130.9, 132.8,
133.5, 135.9, 137.6, 139.4, 172.5, 193.8, and 193.9.
1,5-bis(4-Bromophenyl)-1,3,5-pentanetrione (3h)
Acetone was condensed with methyl 4-bromobenzoate (1:2) using the
general procedure to afford 2.54 g of 3h, light yellow crystals. IR:
ꢀ
1
1589 cmꢁ1. H NMR (DMF-d7 at 85 C): d 2.91 (s), 3.05 (s), 4.51 (s),
4.65 (s), 6.63 (s), 6.86 (s), 7.88–7.94 (m), and 8.03–8.18 (m). 13C NMR
(DMF-d7 at 85 ꢀC): d 50.1, 54.0, 98.1, 98.6, 126.4, 128.6, 128.8, 129.4,
130.9, 132.5, 133.3, 138.5, 172.9, 193.8, and 194.0. Anal. calcd. for
C17H12Br2O7: C, 48.15; H, 2.85. Found: C, 47.75; H, 2.60.
1,5-bis(40-(1,1-Dimethylethyl)phenyl)-1,3,5-pentanetrione (3i)
Acetone was condensed with methyl 4-(1,1-dimethylethyl)benzoate (1:2)
using the general procedure to afford 1.56 g of 3h, yellow crystals. IR:
1
1600 cmꢁ1. H NMR (CDCl3): d 1.32–1.34 (m), 4.08 (s), 4.15 (s), 5.99
(s), 6.29 (s), 7.43–7.51 (m), 7.78–7.81 (app. d, J ¼ 8.7 Hz), and
7.96–7.99 (app. d, J ¼ 8.7 Hz). 13C NMR (CDCl3): d 31.3, 31.4, 51.1,
53.9, 96.6, 96.7, 125.8, 125.9, 126.1, 126.6, 127.3, 127.5, 129.1, 131.2,
131.4, 134.0, 155.6, 156.7, 157.9, 173.9, 182.3, 190.9, 193.8, and 194.8.
Anal. calcd. for C25H30O3ꢅ5=9 H2O: C, 77.29; H, 8.07. Found: C,
77.08; H, 7.93.
Preparation of 2,6 Diaryl-4H-pyran-4-ones (4a-i)
A 10 to 15 mL sample of conc. sulfuric acid was slowly stirred and
cooled to 0 ꢀC, and 1.00 g of dry solid 1,5-diaryl-1,3,5-pentanetrione
was slowly added during 5–10 min. When complete solution had
occurred, it was poured into a beaker containing 50–75 g of ice. The
mixture containing precipitated product was filtered, washed with water,
partially dried by suction after filtration, and recrystallized with ethanol
or ethanol=water.

1,5-Diaryl-1,3,5-pentanetriones
2477
Data
2,6-Diphenyl-4H-pyran-4-one (4a)
This compound was prepared with 3a using the acid cyclization pro-
cedure. IR: 1660 cmꢁ1 1H NMR (CDCl3): d 6.84 (s, 2H), 7.53–7.56
.
(m, 6H), and 7.86–7.89 (m, 4H). 13C NMR (CDCl3): d 111.0, 125.8,
129.0, 131.1, 131.4, 163.4, and 180.1.
2,6-bis(4-Methoxyphenyl)-4H-pyran-4-one (4b)
This compound was prepared with 3b using the acid cyclization
procedure. IR: 1635 cmꢁ1 1H NMR (CDCl3): d 3.91 (s, 6H), 6.90
.
(s, 2H), 7.07–7.10 (m, 4H), and 7.92–7.95 (m, 4H). 13C NMR (DMSO-
d6=CDCl3): d 55.2, 107.2, 114.5, 122.1, 127.9, 162.5, 164.9, and 179.1.
2,6-bis(3,4-Dimethoxyphenyl)-4H-pyran-4-one (4c)
This compound was prepared with 3c using the acid cyclization
procedure. IR: 1643 cmꢁ1 1H NMR (CDCl3=DMSO-d6 at 90 ꢀC):
.
d 3.06 (s, H2O), 3.85 (s, 6H), 3.89 (s, 6H), 6.79 (s, 2H), 7.10–7.13
(d, 2H, J ¼ 8.7 Hz), 7.47 (s, 2H, ArH), and 7.53–7.56 (d, 2H, J ¼ 8.4 Hz).
13C NMR (DMSO-d6=CDCl3): d 56.7, 56.8, 110.3, 110.7, 113.4, 120.1,
124.6, 150.2, 152.6, 163.0, and 179.4.
2,6-bis(3,4,5-Trimethoxyphenyl)-4H-pyran-4-one (4d)
This compound was prepared with 3d using the acid cyclization
procedure. IR: 1654 cmꢁ1 1H NMR (CDCl3): d 3.93 (s, 6H), 3.95
.
(s, 12H), 6.76 (s, 2H), and 7.07 (s, 2H). 13C NMR (CDCl3): d 56.7,
61.6, 103.7, 111.5, 127.2, 141.5, 154.2, 163.7, and 180.8. Anal. calcd.
for C23H24O8ꢅ2 H2O: C, 59.48; H, 6.08. Found: C, 59.11; H, 6.12.
2,6-bis(3,5-Dimethoxyphenyl)-4H-pyran-4-one (4e)
This compound was prepared with 3e using the acid cyclization
procedure. IR: 1645 cmꢁ1 1H NMR (DMSO-d6=CDCl3 at 90 ꢀC):
.
d 3.07 (s, H2O), 3.85 (s, 12H), 6.70 (s, 2H), 6.93 (s, 2H), and 7.10
(s, 4H). 13C NMR (DMSO-d6=CDCl3 at 90 ꢀC): d 56.3, 104.4, 105.0,
112.2, 133.9, 161.9, 162.8, and 179.5. Anal. calcd. for C21H20O6ꢅ1=4
H2O: C, 67.64; H, 5.54. Found: C, 67.74; H, 5.47.

2478
J. D. Knight et al.
2,6-bis(4-Fluorophenyl)-4H-pyran-4-one (4f)
This compound was prepared with 3f using the acid cyclization pro-
1
cedure. IR: 1649 cmꢁ1. H NMR (CDCl3): d 3.57 (s, H2O), 6.99 (s, 2H,
CH), 7.39–7.44 (m, 4H), 8.08–8.13 (app. t, 4H). 13C NMR (DMSO-
d6=CDCl3): d 110.8, 116.4–116.7 (ArC, JCF ¼ 86.7 Hz), 127.5 (ArC,
JCF ¼ 12.3 Hz), 128.7–128.8 (JCF ¼ 35.1 Hz), 161.5–162.3 (JCF ¼ 258 Hz),
Hz), 165.6, and 178.9. 19F NMR (DMSO-d6): d ꢁ109.10-(ꢁ) 109.00
(m, 1 F). Anal. calcd. for C17H10F2O2ꢅ5=3 H2O: C, 64.97; H, 4.28. Found:
C, 64.90; H, 4.09.
2,6-bis(4-Chlorophenyl)-4H-pyran-4-one (4g)
This compound was prepared with 3g using the acid cyclization
procedure. IR: 1648 cmꢁ1 1H NMR (CDCl3=DMSO-d6 at 90 ꢀC):
.
d 3.09 (s, H2O), 6.91 (s, 2H, CH), 7.58–7.61 (d, 4H, ArH, J ¼ 8.7 Hz),
and 7.98–8.01 (d, 4H, J ¼ 8.7 Hz). 13C NMR (DMSO-d6=CDCl3):
d 112.1, 128.5, 129.9, 130.6, 137.0, 162.2, and 179.1.
2,6-bis(4-Bromophenyl)-4H-pyran-4-one (4h)
This compound was prepared with 3h using the acid cyclization
procedure. IR: 1649 cmꢁ1 1H NMR (CDCl3=DMSO-d6 at 90 ꢀC):
.
d 2.86 (s, H2O), 6.82 (s, 2H, CH), 7.68–7.70 (d, 4H, J ¼ 8.7 Hz), and
7.80–7.83 (d, 4H, J ¼ 8.7 Hz). 13C NMR (DMSO-d6=CDCl3): d 112.0,
125.9, 128.1, 130.9, 132.7, 162.4, and 179.1.
2,6-bis(40-(1,1-Dimethylethyl)phenyl)-4H-pyran-4-one (4i)
This compound was prepared with 3i using the acid cyclization
procedure. IR: 1649 cmꢁ1 1H NMR (CDCl3=DMSO-d6 at 90 ꢀC):
.
d 1.34 (s, 9H, CH3), 3.03 (s, 2H, H2O), 6.84 (s, 2H, CH), 7.58–7.61
(d, 2H, J ¼ 8.4 Hz), and 7.91–7.94 (d, 2H, J ¼ 8.7 Hz). 13C NMR
(DMSO-d6=CDCl3 at 90 ꢀC): d 30.4, 34.2, 110.0, 125.4, 125.5, 128.1,
154.1, 162.1, and 178.2. Anal. calcd. for C25H28O2ꢅ1=8 H2O: C, 82.78;
H, 7.88. Found: C, 82.77; H, 7.82.
ACKNOWLEDGMENTS
We thank the following sponsors: the Research Corporation, the
National Science Foundation (Grants CHE 9708014 and 0212699 for

1,5-Diaryl-1,3,5-pentanetriones
2479
Research at Undergraduate Institutions), the United States Department
of Agriculture (NRICGP 2003-35504-12853), and the Petroleum
Research Fund, administered by the American Chemical Society. The
College of Charleston awarded summer grants through its Summer
Undergraduate Research Forum (SURF-2006) to J. D. Knight.
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