Stereoselective one-pot, three-component synthesis of 4-aryltetrahydropyran via Prins-Friedel-Crafts reaction

Article abstract of DOI:10.1021/jo802531h

A diastereoselective one-pot, three-component Prins-Friedel-Crafts reaction was developed for the synthesis of 4-aryltetrahydropyran derivatives from the reaction of carbonyl compounds with homoallylic alcohol in the presence of arene promoted by boron tr

Full text of DOI:10.1021/jo802531h

as C-4 oxygenated, C-4 halogenated, and C-4 azido tetrahy-
dropyran.7 The 4-aryltetrahydropyrans are core units of many
naturally occurring biologically active compounds.8,2h There are
few methods for the synthesis of 4-aryltetrahydropyran. Li et
al.8d have reported the synthesis of 2,4-diaryltetrahydropyran
by a three-component Prins-Friedel-Crafts reaction, but it
suffers a major drawback. The method is limited to aromatic
nucleophiles having a methoxy group. Rychnovsky and his
group applied Prins reaction to 4-allyl-1,3-dioxanes2i and allyl
R-acetoxy ether2h for the synthesis of the 4-aryltetrahydropyran
unit. Recently we have developed methodologies for the
synthesis of symmetric 2,4-disubstituted-4-amido-9 and -4-
aryltetrahydropyran10 by Sakurai-Hosomi-Prins-Ritter and
Sakurai-Hosomi-Prins-Friedel-Crafts reaction, respectively.
Although the Sakurai-Hosomi-Prins-Friedel-Crafts reaction
provides symmetrical 4-aryltetrahydropyran with excellent ster-
eochemistry it fails to afford unsymmetrical 2,6-disubstituted-
4-aryltetrahydropyran. Here we wish to report an efficient
method for the synthesis of unsymmetrical 2,6-disubstituted-
4-aryltetrahydropyran from carbonyl compound, homoallyl
alcohol, and arene mediated by boron trifluoride etherate in
excellent yield and stereoselectivity.
Stereoselective One-Pot, Three-Component
Synthesis of 4-Aryltetrahydropyran via
Prins-Friedel-Crafts Reaction
U. C. Reddy, S. Bondalapati, and Anil K. Saikia*
Department of Chemistry, Indian Institute of Technology
Guwahati, Guwahati 781039, India
asaikia@iitg.ernet.in
ReceiVed NoVember 14, 2008
A diastereoselective one-pot, three-component Prins-
Friedel-Crafts reaction was developed for the synthesis of
4-aryltetrahydropyran derivatives from the reaction of car-
bonyl compounds with homoallylic alcohol in the presence
of arene promoted by boron trifluoride etherate.
Initially benzaldehyde was reacted with homoallyl alcohol
in the presence of boron trifluoride etherate in benzene at rt.
The product 2,4-diphenyltetrahydropyran was obtained with
75% yield in 6 h. The reaction is stereoselective and both
substituents are in the equatorial position. The reaction can be
generalized as shown in Scheme 1.
Multicomponent reactions are important in organic synthesis
due to their ability to form multiple bonds in a single step.1
Tetrahydropyran unit is found in many biologically active
natural products.2 These are prepared by hetero-Diels-Alder
methods,3 manipulations of carbohydrates,4 intramolecular
Michael reactions,5 and other methods.6 Prins reaction has long
been used for the synthesis of 4-substituted tetrahydropyran such
To prove its general applicability, aliphatic, aromatic, unsat-
urated, and heterocyclic aldehydes were examined and it was
found that all types of aldehydes give good yields with high
stereoselectivity (Table 1).
(5) (a) Clarke, P. A.; Santos, S.; Martin, W. H. C. Green Chem. 2007, 9,
438. (b) Clarke, P. A.; Martin, W. H. C.; Hargreaves, M. J.; Wilson, C.; Blake,
A. J. Org. Biomol. Chem. 2005, 3, 3551. (c) Little, R. D.; Masjedizadeh, M. R.;
Wallquist, O.; McLoughlin, J. I. Org. React. 1995, 47, 661.
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Tietze, L. F. Chem. ReV. 1996, 96, 115. (c) Khan, A. T.; Choudhury, L. H.;
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K. R.; Anbarasan, P. Tetrahedron 2007, 63, 1089. (c) Avery, T. D.; Caiazza,
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C. L. Org. Lett. 2002, 4, 577. (b) Hu, Y.; Skalitzky, D. J.; Rychnovsky, S. D.
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R. A.; Parker, G. D.; Roe, R.; Willis, C. L. Chem. Commun. 2005, 3727. (e)
Yadav, J. S.; Reddy, B. V. S.; Maity, T.; Kumar, G. G. K. S. Tetrahedron Lett.
2007, 48, 8874. (f) Yadav, J. S.; Reddy, B. V. S.; Maity, T.; Kumar, G. G. K. S.
Tetrahedron Lett. 2007, 48, 7155. (g) Chan, K.-P.; Seow, A.-H.; Loh, T.-P.
Tetrahedron Lett. 2007, 48, 37. (h) Yadav, J. S.; Reddy, B. V. S.; Kumar,
G. G. K. S. N.; Swamy, T. Tetrahedron Lett. 2007, 48, 2205. (i) Yadav, J. S.;
Reddy, B. V. S.; Kumar, G. M.; Murthy, C. V. S. R. Tetrahedron Lett. 2001,
42, 89. (j) Li, C.-J.; Zhang, W.-C. Tetrahedron 2000, 56, 2406. (k) Zhang, W.-
C.; Viswanathan, G. S.; Li, C.-J. Chem. Commun. 1999, 291.
(8) (a) Gewali, M. B.; Tezuka, Y.; Banskota, A. H.; Ali, M. S.; Saiki, I.;
Dong, H.; Kadota, S. Org. Lett. 1999, 01, 1733. (b) Tezuka, Y.; Gewali, M. B.;
Ali, M. S.; Banskota, A. H.; Kadota, S. J. Nat. Prod. 2001, 64, 208. (c) Kadota,
S.; Tezuka, Y.; Prasain, J. K.; Ali, M. S.; Banskota, A. H. Curr. Top. Med.
Chem. 2003, 03, 203. (d) Yang, X.-F.; Wang, M.; Zhang, Y.; Li, C.-J. Synlett
2005, 1912. (e) Brown, E.; Bijardin, G.; Maudet, M. Tetrahedron 1997, 53,
9679. (f) Nagasaki, T.; Yasuda, S.; Imai, T. Phytochemistry 2001, 58, 833.
(9) Reddy, U. C.; Raju, B. R.; Kumar, E. K. P.; Saikia, A. K. J. Org. Chem.
2008, 73, 1628.
(2) (a) Clarke, P. A.; Santos, S. Eur. J. Org. Chem. 2006, 2045, and references
cited therein. (b) Perron, F.; Albizati, K. F. J. Org. Chem. 1987, 52, 4130. (c)
Class, Y. J.; DeShong, P. Chem. ReV. 1995, 95, 1843. (d) Kopecky, D. J.;
Rychnovsky, S. D. J. Am. Chem. Soc. 2001, 123, 8420. (e) Wang, Y.; Janjic, J.;
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Floreancig, P. E. Angew. Chem., Int. Ed. 2005, 44, 3485. (g) Bahnck, K. B.;
Rychnovsky, S. D. Chem. Commun. 2006, 2388. (h) Tian, X. T.; Jaber, J. J.;
Rychnovsky, S. D. J. Org. Chem. 2006, 71, 3176. (i) Hu, Y.; Skalitzky, D. J.;
Rychnovsky, S. D. Tetrahedron Lett. 1996, 37, 8679.
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70, 2820.
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J. C.; Fairbanks, A. J.; Fleet, G. W. J. Tetrahedron 1998, 54, 13591. (c) Osborn,
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(10) The reaction of aldehyde with allylsilane in arene gives symmetrical
2,6-disubstituted-4-aryltetrahydropyran in good yields. The reaction is highly
stereoselective. Unpublished work.
10.1021/jo802531h CCC: $40.75
Published on Web 02/13/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 2605–2608 2605

TABLE 1. Synthesis of 2,6-Disubstituted-4-aryltetrahydropyran
SCHEME 1. Synthesis of 2,6-Disubstituted-4-phenyl-
tetrahydropyran
In all the cases studied, 4-aryltetrahydropyrans 1b-21b
(Table 1) could be obtained in high purity without any side
products. Both aliphatic and aromatic aldehydes give good yields
with a high degree of diastereoselectivity as determined from
the 1H and 13C NMR spectrum of the crude product. The
substituents on the aromatic ring have a promising effect on
this reaction. The aromatic aldehydes having electron-withdraw-
ing groups and simple benzaldehyde gave good yields compared
to electron-donating groups. Similarly saturated aliphatic alde-
hydes are found to be better substrates than the conjugated
aliphatic aldehydes. This can be attributed to the stability of
the oxocarbenium ion intermediate formed during the reaction
(species 3, Scheme 3).7a,d The electron-donating groups on the
aromatic ring stabilize the oxocarbenium ion whereas the
electron-withdrawing groups destabilize the oxocarbenium ion.
The conformation of the compounds is the chair form and all
three substituents are in the equatorial position. This was
confirmed by NOE experiment and single-crystal X-ray analy-
sis.11
To extend the utility of this method, various arenes as
nucleophiles were systematically investigated under these reac-
tion conditions. It was observed that methyl- and methoxy-
substituted benzene reacts faster than benzene. Thus, the reaction
with toluene gave 22o/p as an inseparable regioisomer with a
ratio of 4.7:1 and 90% overall yield. Similarly o- and m-xylene
gave products 23o/p (85% yield) and 24o/p (88% yield) as a
mixture of two inseparable regioisomers with a ratio of 1:1.2
and 1:2.7, respectively. On the other hand p-xylene gave 25 as
a single isomer with 80% yield. Anisole gave ortho (26o) and
para (26p) regioisomers with an o/p-ratio of 2:1 and 53% and
27% yields, respectively (80% overall yield). On the other hand
1-methoxy-4-methylbenzene gave the single isomer 27 in 82%
yield (Table 2). But fused ring aromatic compounds, for
example, naphthalene, 2-methoxynaphthalene, and deactivated
aromatic compounds, remain unreactive.
The reaction can also be extended to cyclic and symmetrical
acyclic ketones (Scheme 2). The reaction needs to be heated to
40 °C and takes a longer time. Reaction with an unsymmetrical
ketone is not stereoselective. Thus, the reaction of cyclohex-
anone and 1,4-cyclohexanedione at 40 °C gave spirocyclic
compounds 28 and 29 in 56% and 40% yields, respectively.
On the other hand, symmetrical dichloroacetone gave 2,2-bis-
chloromethyl-4-phenyltetrahydropyran 30 in 50% yield. Thus,
it is evident that this reaction has widespread application for
the synthesis of novel bicyclic heterocycles.
The major advantage of this reaction is that in a single step,
tworeactions,primarilythePrinscyclizationandtheFriedel-Crafts
reaction, can be performed without any difficulties.
The mechanism of the reaction can be explained as follows.
In the presence of Lewis acid, homoallylic alcohol 1 reacts with
aldehyde to afford intermediate 2 (Scheme 3). Intermediate 2
(11) Crystallographic data for compound 2b have been deposited with the
Cambridge Crystallographic Data Centre as a supplementary publication number
CCDC 68764.
a Yields refer to isolated yield.
2606 J. Org. Chem. Vol. 74, No. 6, 2009

TABLE 2. Reaction of 3-Buten-1-ol and m-Nitrobenzaldehyde
with Other Nucleophiles (Arenes)
SCHEME 2. Reaction of 3-Buten-1-ol with Ketone
SCHEME 3. Mechanism of the Reaction
mmol) in benzene (2.0 mL) was added drop by drop over 10 min.
The temperature was slowly brought to rt in 1 h. The reaction
mixture was stirred at rt for 6 h. After completion of the reaction,
the product was extracted with ethyl acetate, then washed with brine
and water. The organic layer was dried (Na2SO4) and evaporated
to leave the crude product, which was purified by short column
chromatography over silica gel to give 2,4-diphenyltetrahydropyran
a Yields refer to isolated yield. b Otho/para ratio (26o/26p 2:1).
forms oxocarbenium ion 3, which after cyclization gives
tetrahydropyranyl cation 4. Cation 4 in the presence of arene
neucleophile gives intermediate 5, which after deprotonation
gives the 2,6-disubstituted-4-aryltetrahydropyran 6.
In summary, an efficient and highly diastereoselective one-
pot method has been developed for the synthesis of unsym-
metrical 2,6-disubstituted-4-aryltetrahydropyran. The same method
can also be used for the synthesis of spirocyclic compounds in
good yields. This method should be useful in natural product
synthesis.
1
1b (358 mg, 75%) as a gum. H NMR (400 MHz, CDCl3) δ 1.80
(q, J ) 12.0 Hz, 1 H), 1.85-1.95 (m, 2 H), 2.08 (dquint, J ) 13.2
and 2.0 Hz, 1 H), 2.97 (tt, J ) 11.6 and 4.0 Hz, 1 H), 3.77(dt, J )
11.2 and 3.2 Hz, 1 H), 4.29 (ddd, J ) 11.2, 4.0, and 2.4 Hz, 1 H),
4.48 (dd, J ) 11.2 and 2.0 Hz, 1 H), 7.19-7.40 (m, 10 H); 13C
NMR (100 MHz, CDCl3) δ 33.3, 41.5, 42.0, 68.5, 79.8, 125.7,
126.4, 126.7, 127.4, 128.3, 128.5, 142.9, 145.4; IR 3061, 3029,
2938, 2845, 1494, 1452, 1374, 1252, 1128, 1088, 1041, 961, 918,
751, 701 cm-1. Anal. Calcd for C17H18O: C, 85.67; H, 7.61. Found:
C, 85.55; H, 7.78.
Experimental Section
General Procedure for the Synthesis of Compounds 26 and
27. To a mixture of m-nitrobenzaldehyde (1.0 equiv) in CH2Cl2
(2.0 mL) was added boron trifluoride etherate (1.2 equiv). The
mixture was cooled to 0 °C and then homoallyl alcohol (1.0 equiv)
and nucleophile (arene) (5.0 equiv) in CH2Cl2 (1.0 mL) were added
drop by drop over 10 min. The temperature was slowly brought to
rt in 1 h. The reaction mixture was stirred at rt for a specified time.
The progress of the reaction was monitored by TLC with ethyl
acetate and hexane as eluents. After completion of the reaction,
the product was extracted with ethyl acetate, then washed with brine
and water. The organic layer was dried (Na2SO4) and evaporated
to leave the crude product, which was purified by short column
chromatography over silica gel to give the title compounds.
4-(2-Methoxyphenyl)-2-(3-nitrophenyl)tetrahydropyran (26o)
and 4-(4-Methoxyphenyl)-2-(3-nitrophenyl)tetrahydropyran (26p,
Table 2). To a mixture of m-nitrobenzaldehyde (302 mg, 2.0 mmol)
in CH2Cl2 (2.0 mL) was added boron trifluoride etherate (0.30 mL,
2.4 mmol). The reaction mixture was cooled to 0 °C and then a
General Procedure for the Synthesis of Compounds 1b-21b
and 22-25. To a mixture of aldehydes (1.0 equiv) in arene (3.0
mL) was added boron trifluoride etherate (1.2 eqiuv). The mixture
was cooled to 0 °C and then homoallyl alcohol (1.0 equiv) in arene
(2.0 mL) was added drop by drop over 10 min. The temperature
was slowly brought to rt in 1 h. The reaction mixture was stirred
at rt for a specified time. The progress of the reaction was monitored
by TLC with ethyl acetate and hexane as eluents. After completion
of the reaction, the product was extracted with ethyl acetate, then
washed with brine and water. The organic layer was dried (Na2SO4)
and evaporated to leave the crude product, which was purified by
short column chromatography over silica gel to give the title com-
pounds.
Synthesis of 2,4-Diphenyltetrahydropyran (1b, Table 1). To a
solution of benzaldehyde 1a (0.20 mL, 2.0 mmol) in benzene (3.0
mL) was added boron trifluoride etherate (0.30 mL, 2.4 mmol).
The mixture was cooled to 0 °C and then buten-1-ol (144 mg, 2.0
J. Org. Chem. Vol. 74, No. 6, 2009 2607

solution of 3-buten-1-ol (144 mg, 2.0 mmol) and anisole (1.0 mL,
9.2 mmol) in CH2Cl2 (1.0 mL) was added drop by drop over 10
min. The temperature was then slowly increased to rt in 1 h. The
reaction mixture was stirred at rt for 6 h. After completion of the
reaction, the product was extracted with ethyl acetate, then washed
with brine and water. The organic layer was dried (Na2SO4) and
evaporated to leave the crude product, which was purified by short
column chromatography over silica gel to give 26o/p as two
regioisomers with a ratio 2:1. 26o (334 mg, 53%): solid; mp 79-83
ethyl acetate and hexane as eluents. After completion of the reaction,
the product was extracted with ethyl acetate, then washed with brine
and water. The organic layer was dried (Na2SO4) and evaporated
to leave the crude product, which was purified by short column
chromatography over silica gel.
Synthesis of 4-Phenyl-1-oxa-spiro[5.5]undecane (28, Scheme
2). To a solution of cyclohexanone (196 mg, 2.0 mmol) and 3-buten-
1-ol (144 mg, 2.0 mmol) in benzene (3.0 mL) was added boron
trifluoride etherate (0.30 mL, 2.4 mmol). The reaction mixture was
stirred at 40 °C for 16 h. After completion of the reaction, the
product was extracted with ethyl acetate, then washed with brine
and water. The organic layer was dried (Na2SO4) and evaporated
to leave the crude product, which was purified by short column
chromatography over silica gel to give 4-phenyl-1-oxa-spiro[5.5]-
undecane 28 (258 mg, 56%) as a gum. 1H NMR (400 MHz, CDCl3)
δ 1.26-1.80 (m, 14 H), 2.10-2.14 (m, 1 H), 2.90-2.97 (m, 1 H),
3.73-3.85 (m, 1 H), 7.18-7.23 (m, 3 H), 7.28-7.33 (m, 2 H);
13C NMR (100 MHz, CDCl3) δ 21.6, 21.8, 26.3, 29.7, 33.7, 36.7,
40.5, 43.6, 60.7, 72.4, 126.3, 126.8, 128.5, 146; IR 3027, 2927,
2855, 1603, 1492, 1445, 1375, 1175, 1101, 1079, 974, 910, 759,
698 cm-1. Anal. Calcd for C16H22O: C, 83.43; H, 9.63. Found: C,
83.54; H, 9.54.
1
°C; H NMR (400 MHz, CDCl3) δ 1.67 (q, J ) 12.0 Hz, 1 H),
1.80-1.95 (m, 2 H), 2.10 (dquint, J ) 13.2 and 2.0 Hz, 1 H), 3.45
(tt, J ) 12.0 and 3.6 Hz, 1 H), 3.77-3.82 (m, 1 H), 3.86 (s, 3 H),
4.31 (ddd, J ) 11.6, 4.4, and 1.6 Hz, 1 H), 4.63 (dd, J ) 11.2 and
2.0 Hz, 1 H), 6.86-7.00 (m, 2 H), 7.16-7.23 (m, 2 H), 7.50 (t, J
) 8.0 Hz, 1 H), 7.71 (d, J ) 7.6 Hz, 1 H), 8.10 (d, J ) 8.4 Hz, 1
H), 8.28 (s, 1 H); 13C NMR (100 MHz, CDCl3) δ 31.8, 34.8, 40.4,
55.5, 69.1, 78.9, 110.6, 120.9, 121.1, 122.5, 126.7, 127.5, 129.4,
132.2, 133.1, 145.4, 148.4, 156.9; IR 2939, 2841, 1600, 1528, 1493,
1349, 1240, 1132, 1083, 1030, 846, 810, 753 cm-1. Anal. Calcd
for C18H19NO4: C, 68.99; H, 6.11; N, 4.47. Found: C, 68.95; H,
1
6.14; N, 4.52. 26p (167 mg, 27%): gum; H NMR (400 MHz,
CDCl3) δ 1.65 (q, J ) 12.0 Hz, 1 H), 1.82-1.91 (m, 2 H), 2.09
(dquint, J ) 13.2 and 2.0 Hz, 1 H), 2.93 (tt, J ) 12.0 and 3.6 Hz,
1 H), 3.71-3.80 (m, 1 H), 3.77 (s, 3 H), 4.31 (dt, J ) 10.8 and 1.2
Hz, 1 H), 4.56 (dd, J ) 10.8 and 1.6 Hz, 1 H), 6.85 (d, J ) 8.8 Hz,
2 H), 7.15 (d, J ) 8.8 Hz, 2 H), 7.48 (t, J ) 8.0 Hz, 1 H), 7.69 (d,
J ) 7.6 Hz, 1 H), 8.10 (dd, J ) 8.4 and 1.2 Hz, 1 H), 8.27 (s, 1
H); 13C NMR (100 MHz, CDCl3) δ 33.4, 41.1, 41.9, 55.3, 68.7,
78.6, 114.1, 120.9, 122.4, 127.7, 129.4, 132.0, 137.2, 145.2, 148.3,
158.3; IR 2935, 2847, 1610, 1528, 1463, 1351, 1249, 1180, 1086,
1036, 830, 807, 738 cm-1. Anal. Calcd for C18H19NO4: C, 68.99;
H, 6.11; N, 4.47. Found: C, 69.04; H, 6.08; N, 4.55.
Acknowledgment. A.K.S. is grateful to the Department of
Science and Technology (DST), New Delhi, for financial support
(Grant No. SR/S1/OC-33/2007) and C.M.R is grateful to the
Council of Scientific & Industrial Research (CSIR) for a fel-
lowship.
Supporting Information Available: Experimental proce-
1
dures and H, 13C NMR spectra of all compounds, 19F NMR
General Procedure for the Three-Component Reaction with
Ketones 28-30. To a solution of ketone (1 equiv) and 3-buten-ol
(1 equiv) in benzene (3.0 mL) was added boron trifluoride etherate
(1.2 equiv). The reaction mixture was stirred for the specified time
at 40 °C. The progress of the reaction was monitored by TLC with
spectra of 4b and 8b, and X-ray crystallographic data and
ORTEP diagram of 2b. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO802531H
2608 J. Org. Chem. Vol. 74, No. 6, 2009