Palladium(0)-catalyzed synthesis of 2-phenyl-2H-chromene

Article abstract of DOI:10.1081/SCC-120014986

2-Phenyl-2H-chromene is obtained in quite good yield starting from 3-[(2-tert-butyldimethylsilyl)oxyphenyl]prop-2-enal. Condensation of this aldehyde with phenyl magnesium bromide, followed by the acetylation of the alcohol obtained, and then intramolecular cyclization in the presence of a palladium catalyst gave the phenylchromene in an overall 34% yield.

Full text of DOI:10.1081/SCC-120014986

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PALLADIUM(0)-CATALYZED SYNTHESIS OF 2-PHENYL-2H-
CHROMENE
J.-R. Labrosse a , P. Lhoste a & D. Sinou b
a Laboratoire de Synthèse Asymétrique , Associé au CNRS , CPE Lyon , Université Claude
Bernard Lyon 1 , 43, Boulevard du 11 Novembre 1918, Villeurbanne Cédex, 69622, France
b Laboratoire de Synthèse Asymétrique , Associé au CNRS , CPE Lyon , Université Claude
Bernard Lyon 1 , 43, Boulevard du 11 Novembre 1918, Villeurbanne Cédex, 69622, France
Published online: 16 Aug 2006.
To cite this article: J.-R. Labrosse , P. Lhoste & D. Sinou (2002) PALLADIUM(0)-CATALYZED SYNTHESIS OF 2-PHENYL-2H-
CHROMENE, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
32:23, 3667-3674, DOI: 10.1081/SCC-120014986
To link to this article: http://dx.doi.org/10.1081/SCC-120014986
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 23, pp. 3667–3674, 2002
PALLADIUM(0)-CATALYZED SYNTHESIS
OF 2-PHENYL-2H-CHROMENE
*
J.-R. Labrosse,P. Lhoste,and D. Sinou
Laboratoire de Synthese Asymetrique,
Associe au CNRS, CPE Lyon, Universite Claude
Bernard Lyon 1, 43, Boulevard du 11 Novembre 1918,
69622 Villeurbanne Cedex, France
ABSTRACT
2-Phenyl-2H-chromene is obtained in quite good yield start-
ing from 3-[(2-tert-butyldimethylsilyl)oxyphenyl]prop-2-enal.
Condensation of this aldehyde with phenyl magnesium
bromide, followed by the acetylation of the alcohol obtained,
and then intramolecular cyclization in the presence of a
palladium catalyst gave the phenylchromene in an overall
34% yield.
Key Words: 2H-Chromene; Palladium; Cyclization; Allylic
acetate
INTRODUCTION
Flav-3-enes are useful intermediates in the synthesis of the parent
flavans, flavan-3,4-diols and flavylium salts.[1] They are easily isomerized
*Corresponding author. E-mail: sinou@univ-lyon1.fr
3667
DOI: 10.1081/SCC-120014986
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3668
LABROSSE,LHOSTE,AND SINOU
into flav-2-enes that are precursors of biflavonoıds.[2] 4-Aryloxyflavans and
4-aryloxyflavonoıds, whose structures are known to occur in some natural
products, could also be obtained from flav-3-enes.[3]
2-Phenyl-2H-chromene was first obtained by reduction of 20-hydroxy-
chalcone in isopropanol.[1] Dehalogenation of halogenoflavanes gave also
the corresponding 2-phenyl-2H-chromene.[2–5] Various aryl propargyl ethers
have been thermally cyclized via a Claisen rearrangement into the corres-
ponding 2-aryl-2H-chromenes.[6] More recently a palladium(II)-catalyzed
cyclization of various o-allylic phenols to substituted 2H-benzopyrans was
published by Larock et al.[7]
We have recently shown that allylic ethers could be conveniently
prepared in high yields and under very mild conditions via palladium(0)-
catalyzed O-alkylation of allylic carbonates or acetates with alcohols and
phenols.[8,9] This procedure was particularly efficient for the formation of
oxygenated heterocyclic compounds.[10–15] We described in this paper the
application of this very simple procedure for the synthesis of 2-phenyl-2H-
chromene.
DISCUSSION
The sequence for the preparation of 2-phenyl-2H-chromene (8) is
shown in Sch. 1. Wittig reaction between 2-hydroxybenzaldehyde (1) and
the stabilized ylide Ph3P¼CHCO2Et in benzene according to the literature
procedure[16] afforded hydroxy ester 2 in 99% yield as a E/Z mixture (70/30).
Reaction of the (E)-hydroxy ester 2, obtained by column chromatography,
with tert-butyldimethylsilyl chloride in DMF in the presence of
imidazole gave compound 3 in 96% yield. Transformation of ester 3 into
aldehyde 5 was performed in two steps; reduction of the ester 3 with Dibal
in toluene, followed by oxidation with MnO2 in CH2Cl2 afforded the
aldehyde 5 in 82% yield. It is to be noticed that this aldehyde 5 could also
be obtained by a Wittig condensation between 2-hydroxybenzaldehyde and
Ph3P¼CHCHO in benzene[17] (44% yield) followed by the reaction with tert-
butyldimethylsilyl chloride in DMF in the presence of imidazole (64% yield).
However this Wittig reaction gave many by-products.
Reaction of the Grignard reagent obtained from C6H5Br and
magnesium on aldehyde 5 afforded the allylic benzylic alcohol 6a in 79%.
However, since this alcohol is very unstable, the crude product was reacted
directly with acetyl chloride in CH2Cl2 in the presence of pyridine to give the
corresponding acetate 6b (76% yield). Deprotection of the hydroxyl function
of compound 6a in the presence of Bu4NF.H2O afforded the hydroxyacetate
7, which was directly cyclized in the presence of a palladium catalyst, obtained

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SYNTHESIS OF 2-PHENYL-2H-CHROMENE
3669
Scheme 1. Reagents and conditions: (i) Ph3P¼CHCO2Et, C6H6, 99%,Ref. [16];
(ii) TBDMSCl, imidazole, DMF; (iii) Dibal, toluene; (iv) MnO2, CH2Cl2;
(v) C6H5MgBr, diethylether; (vi) CH3COCl, C5H5N, CH2Cl2; (vii) B uNFꢀH2O,
4
THF; (viii) Pd2(dba)3, dppb, THF.
from Pd2(dba)3 and dppb or 1,4-bis(diphenylphosphino)butane in THF to
give the expected 2-phenyl-2H-chromene 8. It is to be noticed that the overall
chemical yield from the aldehyde 5 to the phenyl chromene 8 is 34%.
CONCLUSION
In conclusion, we have devised a new access to 2-phenyl-2H-chromene
occuring under very mild conditions. This palladium-catalyzed synthesis can
be extended to the preparation of various 2-alkyl-2H-chromenes as well as
functionalized 2-aryl-2H-chromenes. Work is currently under progress in
these directions.
EXPERIMENTAL
All manipulations involving palladium-catalysis were carried out in
Schlenk tubes under an inert atmosphere. Tetrahydrofuran was distilled

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3670
LABROSSE,LHOSTE,AND SINOU
from sodium/benzophenone. All 1H NMR and 13C NMR spectra were
recorded on a Varian-Gemini 200 or Brucker AM 300 spectrometers in
CDCl3. Chemical shifts are reported on the ꢀ scale with the reference to
tetramethylsilane as the internal standard. TLC was done using Merck
silica gel 60 F254 precoated aluminium-backed plates, 0.2 mm thickness.
Visualisation was by UV or by spraying with 10% sulphuric acid and then
heating. Column chromatography was carried out using Merck silica gel
(Kieselgel 60 70–230 mesh).
Ethyl (E)-3-[(2-tert-butyldimethylsilyl)oxyphenyl]prop-2-enoate (3):
A solution of t-BuMe2SiCl (3.6 g, 23.2 mmol) and imidazole (3.6 g,
52.9 mmol) in DMF (30 mL) was added at room temperature to a solution
of ethyl (E)-3-(2-hydroxyphenyl)prop-2-enoate[16] (2) (4.0 g, 21 mmol) in
DMF (15 mL). After being stirred at 25ꢀC for 24 h, water (100 mL)
was added, and the mixture was extracted with CH2Cl2 (5 Â 30 mL).
The organic phases are washed with NaOH 5% (5 Â 30 mL), then with
H2O (5 Â 40 mL), and dried over Na2SO4. Evaporation of the solvent
followed by purification of the residue by flash-chromatography using
petroleum ether/ethyl acetate (7 : 1) as the eluent gave 6.2 g of compound
1
3 as an oil (yield 96%). Rf ¼ 0.38; H NMR (300 MHz, CDCl3) ꢀ: 0.23 (s,
6H, SiMe), 1.05 (s, 9H, CMe3), 1.33 (t, J ¼ 7.2 Hz, 3H, CH3), 4.25 (q,
J ¼ 7.2 Hz, 2H, OCH2), 6.38 (d, J ¼ 16.2 Hz, 1H, ¼CH-), 6.84 (dd,
J ¼ 7.9, 1.1 Hz, 1H, Harom), 6.98 (ddd, J ¼ 7.9, 7.4, 1.1 Hz, 1H, Harom),
7.26 (ddd, J ¼ 7.9, 7.4, 1.8 Hz, 1H, Harom), 7.55 (dd, J ¼ 7.9, 1.8 Hz, 1H,
H
arom), 8.09 (d, J ¼ 16.2 Hz, 1H, -CH¼); 13C NMR (75.5 MHz, CDCl3) ꢀ:
À4.2, 14.4, 18.4, 25.8, 60.3, 117.8, 120.0, 121.6, 126.0, 127.3, 131.3, 139.9,
154.6, 167.2. Anal. calcd for C17H26O3Si (306.48): C 66.63, H 8.56, found: C
66.63, H 8.54.
(E)-3-[(2-tert-Butyldimethylsilyl)oxyphenyl]prop-2-enol (4): A solution
of ester 3 (3.0 g, 9.8 mmol) in toluene (60 mL) was slowly added at À78ꢀC to
a solution of Dibal 1.5 M in toluene (16.3 mL, 24.5 mmol). After being
stirred at À78ꢀC for 2 h, methanol (20 mL) was added, and the solution
acidified by HCl 1 N (20 mL). The solution was extracted with CH2Cl2
(5 Â 30 mL), and the organic phase dried over Na2SO4. Evaporation of
the solvent followed by purification of the residue by flash-chromatography
using petroleum ether/ethyl acetate (4 : 1) as the eluent gave 2.44 g of
1
compound 4 as an oil (yield 94%). Rf ¼ 0.42; H NMR (300 MHz, CDCl3)
ꢀ: 0.23 (s, 6H, SiMe), 1.05 (s, 9H, CMe3), 1.55 (bs, 1H, OH),
4.32 (d, J ¼ 6.1 Hz, 2H, CH2OH), 6.31 (dt, J ¼ 16.0, 6.1 Hz, 1H, ¼CH-),
6.80 (dd, J ¼ 8.1, 0.9 Hz, 1H, Harom), 6.93 (ddd, J ¼ 7.7, 7.3, 0.9 Hz, 1H,
H
H
arom), 6.95 (d, J ¼ 16.0 Hz, 1H, -CH¼), 7.13 (ddd, J ¼ 8.1, 7.3, 1.8 Hz, 1H,
arom), 7.47 (dd, J ¼ 7.7, 1.8 Hz, 1H, Harom); 13C NMR (75.5 MHz , CDCl3)
ꢀ: À4.1, 18.4, 25.9, 64.3, 119.7, 121.5, 126.5, 126.6, 128.1, 128.4, 128.6, 153.0.

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SYNTHESIS OF 2-PHENYL-2H-CHROMENE
3671
Anal. calcd for C15H24O2Si (264.45): C 68.14, H 9.16, found: C 67.91,
H 8.66.
(E)-3-[(2-tert-Butyldimethylsilyl)oxyphenyl]prop-2-enal (5): Method A:
A mixture of 3-[(2-t-butylmethylsilyl)oxyphenyl]prop-2-enol 4 (4.49 g,
17.0 mmol) and MnO2 85% (53.0 g, 0.52 mol) in CH2Cl2 (10 mL) was stirred
at room temperature for 3 h. After filtration of the solid on Celite and
evaporation of the solvent, the residue was purified by flash-chromatog-
raphy using petroleum ether/ethyl acetate (8 : 1) as the eluent to give 3.97 g
of compound 5 as an oil (yield 89%). Method B: A solution of t-BuMe2SiCl
(2.24g, 14.8 mmol) and imidazole (2.3 g, 33.7 mmol) in DMF (15 mL) was
added at room temperature to a solution of (E)-3-(2-hydroxyphenyl)prop-2-
enal[17] (2.0 g, 13.5 mmol) in DMF (15 mL). After being stirred at 25ꢀC for
24 h, water (100 mL) was added, and the mixture was extracted with CH2Cl2
(5 Â 30 mL). The organic phases are washed with NaOH 5% (3 Â 30 mL),
then with H2O (7 Â 40 mL), and dried over Na2SO4. Evaporation of the
solvent followed by purification of the residue by flash-chromatography
using petroleum ether/ethyl acetate (8 : 1) as the eluent gave 2.25 g of
1
compound 5 as an oil (yield 64%). Rf ¼ 0.35; H NMR (300 MHz, CDCl3)
ꢀ: 0.25 (s, 6H, SiMe), 1.05 (s, 9H, CMe3), 6.70 (dd, J ¼ 16.2, 7.7 Hz, 1H,
¼CH-), 6.88 (dd, J ¼ 8.1, 0.7 Hz, 1H, Harom), 7.01 (ddd, J ¼ 7.7, 7.4, 0.7 Hz,
1H, Harom), 7.32 (ddd, J ¼ 8.1, 7.4, 1.7 Hz, 1H, Harom), 7.55 (dd, J ¼ 7.7,
1.7 Hz, 1H, Harom), 7.89 (d, J ¼ 16.2 Hz, 1H, -CH¼), 9.67 (d, J ¼ 7.7 Hz, 1H,
CHO); 13C NMR (75.5 MHz, CDCl3) ꢀ: À4.1, 18.4, 25.8, 119.9, 121.7, 125.5,
127.8, 128.3, 132.5, 148.3, 154.9, 194.0. Anal. calcd for C15H22O2Si (262.43):
C 68.67, H 8.46, found: C 68.55, H 8.62.
(E)-3-[(2-tert-Butyldimethylsilyl)oxyphenyl]-1-phenylprop-2-enol (6a):
A solution of compound 5 (2.0 g, 7.6 mmol) in diethylether (5 mL) was
slowly added at 0ꢀC to a solution of the Grignard reagent obtained from
bromobenzene (3.6 g, 22.3 mmol) and Mg (0.56 g, 22.3 at.g) in diethylether
(100 mL). After being stirred at 25ꢀC for 24 h, a saturated aqueous ammo-
nium chloride solution (60 mL) was added, the mixture was extracted with
diethylether (3 Â 20 mL), and the organic phase was dried over Na2SO4.
Evaporation of the solvent gave the crude alcohol 6a which was used with-
out further purification. Rf ¼ 0.56 (eluent petroleum ether/ethyl acetate 7 : 1);
1H NMR (300 MHz, CDCl3) ꢀ: 0.18 (s, 3H, SiMe), 0.19 (s, 3H, SiMe), 0.99
(s, 9H, CMe3), 2.02 (bs, 1H, OH), 5.38 (d, J ¼ 6.5 Hz, 1H, CHOH), 6.35 (dd,
J ¼ 16.0, 6.5 Hz, 1H, ¼CH-), 6.95 (d, J ¼ 16.0 Hz, 1H, -CH¼), 6.70–7.50 (m,
9H, Harom); 13C NMR (75.5 MHz, CDCl3) ꢀ: À4.2, À4.1, 18.4, 25.9, 75.6,
119.6, 121.4, 126.2, 126.4, 126.6, 127.7, 127.9, 128.6, 128.7, 131.5, 143.0, 153.1.
Acetic Acid (E)-3-[(2-tert-butyldimethylsilyl)oxyphenyl]-1-phenylprop-
2-enol ester (6b): To a solution of crude alcohol 6a (1.7 g, 6.5 mmol) and
pyridine (2.1 mL, 25.9 mmol) in CH2Cl2 (25 mL) was slowly added at 0ꢀC

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3672
LABROSSE,LHOSTE,AND SINOU
acetyl chloride (1.89 mL, 25.9 mmol). After being stirred at 25ꢀC for 24 h, an
aqueous saturated copper sulfate solution (20 mL) was added, the mixture
was extracted with diethylether (3 Â 15 mL), and the organic phase was
dried over Na2SO4. Evaporation of the solvent gave 1.7 g of the crude
acetate 6b (yield 76%) which was used without further purification for the
next step. Rf ¼ 0.45 (eluent petroleum ether/ethyl acetate 12 : 1 þ 1% Et3N);
1H NMR (300 MHz, CDCl3) ꢀ: 0.19 (s, 3H, SiMe), 0.20 (s, 3H, SiMe), 0.99
(s, 9H, CMe3), 2.14 (s, 3H, CH3), 6.32 (dd, J ¼ 15.9, 5.9 Hz, 1H, ¼CH-), 6.47
(d, J ¼ 5.9 Hz, 1H, CHO), 6.70–7.50 (m, 10H, -CH¼, Harom); 13C NMR
(75.5 MHz, CDCl3) ꢀ: À4.2, À4.1, 18.4, 21.4, 25.9, 76.4, 119.7, 121.4,
126.6, 127.3, 127.5, 127.6, 127.7, 128.2, 128.7, 128.9, 139.5, 153.1, 170.0.
Acetic Acid (E)-3-(2-hydroxyphenyl)-1-phenylprop-2-enol ester (7): To
a solution of crude acetate 6b (1.19 g, 4.6 mmol) in THF (25 mL) was added
a solution of Bu4NF.H2O (1.63 g, 62.4 mmol). After being stirred at 25ꢀC for
1 h, the solvent was evaporated and the residue treated with diethylether
(50 mL). The diethylether solution was washed with water (3 Â 20 mL) and
dried over Na2SO4. Evaporation of the solvent gave 0.76 g of the crude
acetate 7 (yield 76%) which was used without further purification for the
next step.
Synthesis of 2-phenyl-2H-chromene (8): The catalytic system was
prepared by stirring for 0.5 h in a Schlenk tube under argon Pd2dba3
[or dipalladiumtris(dibenzylideneacetone)] (51.2 mg, 0.056 mmol) and 1,4-
bis(diphenylphosphino)butane or dppb (95.5 mg, 0.224 mmol) in tetra-
hydrofuran (7 mL). This solution was added under argon to a Schlenk tube
containing the acetate 7 (300 mg, 1.12 mmol) and Et3N (0.23 mL, 1.68 mmol)
in THF (7 mL). After being stirred for 24 h, the solvent was evaporated and
the residue purified by flash-chromatography using petroleum ether/ethyl
acetate (15 : 1) as the eluent to give 73.7 mg of 2-phenyl-2H-chromene (yield
1
76%). Rf ¼ 0.36; H NMR (300 MHz, CDCl3) ꢀ: 5.82 (dd, J ¼ 9.9, 3.3 Hz,
1H, ¼CH-), 5.94 (bs, 1H, OCH), 6.56 (dd, J ¼ 9.9, 0.9 Hz, 1H, -CH¼),
6.70–7.50 (m, 9H, Harom); 13C NMR (75.5 MHz, CDCl3) ꢀ: 77.3, 116.1,
121.3, 121.4, 124.1, 125.0, 126.7, 128.5, 128.7, 129.6, 140.9, 153.3. These
values are in quite agreement with the literature.[18]
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SYNTHESIS OF 2-PHENYL-2H-CHROMENE
3673
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Received in the UK September 11, 2001