Novel synthesis of 1,3-disubstituted alkyl- and aralkylnaphthalenes from methylenetriphenylphosphorane, 1,1-disubstituted epoxides, paraformaldehyde, and trimethylsilyl triflate

Article abstract of DOI:10.1246/cl.2002.438

A novel approach toward the synthesis of 3-methylnaphthalenes is achieved by the reaction of 3-methylene-5,5-disubstituted tetrahydrofurans derived from methylenetriphenylphosphorane, 1,1-disubstituted epoxides and paraformaldehyde with trimethylsilyl trifluoromethanesulfonate in the presence of diisopropylethylamine.

Full text of DOI:10.1246/cl.2002.438

438
Chemistry Letters 2002
Novel Synthesis of 1,3-Disubstituted Alkyl- and Aralkylnaphthalenes from
Methylenetriphenylphosphorane, 1,1-Disubstituted Epoxides, Paraformaldehyde, and
Trimethylsilyl Triflate
Kentaro Okuma,ꢀ Yoshitaka Hirose, and Kosei Shioji
Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180
(Received January 10, 2002; CL-020035)
Table 1. One-pot synthesis of 4-methylenetetrahydrofurans 2a
A novel approach toward the synthesis of 3-methylnaphtha-
lenes is achieved by the reaction of 3-methylene-5,5-disubstituted
tetrahydrofurans derived from methylenetriphenylphosphorane,
1,1-disubstituted epoxides and paraformaldehyde with trimethyl-
silyl trifluoromethanesulfonate in the presence of diisopropyl-
ethylamine.
Epoxide 4
Products (Yields/%)
5
Ar
Ph
R
Reaction Time/h
2
Ph
p-Tol
p-ClC6H4
Me
1
3
2
3
3
2a 54 5a 21
2b 42 5b 47
2c 42 5c 36
2d 50 5d 31
2e 43 5e 25
p-Tol
p-ClC6H4
Ph
3,4-(MeO)2C6H3 Me
Naphthalenes are important substances for their structural
and biological aspects and their industrial uses.1 The synthetic
methods of naphthalenes include a thermal dehydroaromatization
of hydrocarbons by using catalysts,2 annulation initiated by the
addition of a benzylic sulfone anion to methyl crotonate,3 ring-
closure reaction of o-allylbenzamides with MeLi or LDA,4 and
cycloaddition reaction of tetraarylcyclopentadienone with
benzyne.3;5 These methods require higher reaction temperature
(300–500 ꢁC) or multi-step reactions. Recently, we have reported
the novel formation of tetrahydropyrans from methylene-1,3-
dioxepanes.6 In the course of the synthetic application of 2,2,2-
triphenyl-2,1ꢀ5-oxaphospholanes (1), we have found unusual
formation of exomethylenetetrahydrofurans (2) in the reaction
with paraformaldehyde. We report herein a regiospecific
synthesis of 1,3-disubstituted naphthalenes (3) from 2, trimethyl-
silyl trifluoromethanesulfonate, and diisopropylethylamine.
2,2-Disubstituted 4-methylenetetrahydrofurans (2) were
synthesized by the reaction of methylenetriphenylphosphorane,
1,1-diphenylethylene oxide (4a), and paraformaldehyde. Treat-
ment of methylenetriphenylphosphorane with 4a followed by the
addition of paraformaldehyde in refluxing benzene resulted in the
formation of 2a in 54% yield (Scheme 1). Other reactions were
carried out in a similar manner (Table 1). In every cases, the
corresponding homoallylic alcohols (5), normal Wittig reaction
products, were obtained as side products.
aThe reaction was carried out in refluxing benzene.
Scheme 2.
Scheme 3.
(8) produced from 3,3-ditolyl-3-hydroxypropyltriphenylpho-
sphonium iodide (9) and butyllithium, only the corresponding
homoallylic alcohol 5b was obtained in 86% yield (Scheme 3).
We first attempted ring opening reaction of 2 in the hope of
obtaining diols. By using catalytic amount of HCl, trifluoro-
methanesulfonic acid, and trifluoroacetic acid, THF 2 led to
unidentified polymeric mixtures. Gassman et al. found that the
reaction of acetals with trimethylsilyl trifluoromethanesulfonate
(TMSOTf) in the presence of diisopropylethylamine gave vinyl
enol ethers in good yields.7 In view of these results, we then
applied this method to tetrahydrofurans. THF 2a was treated with
TMSOTf in the presence of diisopropylethylamine at room
temperature to give the corresponding naphthalene 3a in 82%
yield (Scheme 4). The results were summarized in Table 2. Three
equivalent of diisopropylethylamine must be required for
completion. Other bases such as triethylamine gave 3 in much
Scheme 1.
The reaction might proceed as follows: In refluxing benzene,
ylide reacted with epoxide to give the corresponding oxaphos-
pholane 1, which reacted with paraformaldehyde to give the
corresponding betaine (6). Diol 7 was produced by attacking of
another molar of formaldehyde, which finally dehydrated to
afford 2 (Scheme 2).
Oxaphospholane 1 plays an important role for the formation
of 2. If the present reaction was carried out by using ꢁ-oxideylide
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
439
Scheme 4.
Table 2. Reaction of 1 with TMSOTf8
2
Conditions
R0 Time/h Base/equiv
Product (Yield/%)
3
R
2a
2a
Ph
Ph
H
H
6
6
6
6
6
2
3
3
3
3
3a
3a
3b
3c
3d
36
82
90
86
73
2b p-Tol Me
2c p-ClC6H4 Cl
2d
Me
H
Scheme 6.
lower yields.
Winterman, J. Chem. Soc., Chem. Commun., 1968, 723. For a
review, see N. Campbell, ‘‘Rodd’s Chemistry of Carbon
Compounds,’’ ed. by S. Coffey, Elzsevier, Amsterdam
(1978), Vol. IIIg, Chap. 27.
R. P. Linstead and S. L. S. Thomas, J. Chem. Soc., 1940, 1127;
H. M. Liu, B. L. Tian, and Y. D. Xu, Appl. Catal., A, 213, 103
(2001); A. T. Mathauser and A. V. Teplyakov, Catal. Lett., 73,
207 (2001).
During the investigation on lignan group, Haworth and
Atkinson reported the synthesis of 6,7-dimethoxy-1,3-dimethyl-
naphthalene (3e) via six-step reactions from veratrylacetyl
chloride.9 We then applied the present method to the synthesis
of 3e starting from 3,4-dimethoxyacetophenone. As shown in
Scheme 5, naphthalene 3e was synthesized regiospecifically.
2
3
4
T. T. Hoye, M. Chen, B. Hoang, L. Mi, and O. P. Priest, J. Org.
Chem., 64, 7184 (1999).
M. P. Sibi, J. W. Dankwardt, and V. Snieckus, J. Org. Chem.,
51, 271 (1986).
5
6
F. M. Beringer and S. J. Huang, J. Org. Chem., 29, 445 (1964).
K. Okuma, S. Hayano, K. Shioji, and H. Matsuyama,
Tetrahedron Lett., 41, 2171 (2000).
7
8
P. G. Gassman, S. J. Burns, and K. B. Pfister, J. Org. Chem.,
58, 1449 (1993).
Satisfactory mass spectra and/or elemental analyses were
obtained for all new compounds. Selected 1H NMR data of 2b
and 3c. 2b: 1H NMR (CDCl3) ꢂ ¼ 2:29 (s, 6 H, ArMe), 3.22
(br s, 2 H, CH2), 4.43 (br s, 2H, CH2), 4.83 (br s, 1 H, ¼ CHH),
4.99 (br s, 1 H, ¼ CHH), 7.09 (d, 4 H, J ¼ 8 Hz, p-Tol), 7.29
(d, 4 H, J ¼ 8 Hz, p-Tol). 3c: 1H NMR (CDCl3) ꢂ ¼ 2:53 (s, 3
H, ArMe), 7.22 (br s, 1 H, Ar), 7.29 (dd, 1 H, J ¼ 2 and 8 Hz,
Ar), 7.38 (d, 2 H, J ¼ 8 Hz, p-ClC6H4-), 7.45 (d, 2 H,
J ¼ 8 Hz, p-ClC6H4-), 7.54 (s, 1 H, Ar), 7.70 (d, 1 H,
J ¼ 8 Hz, Ar), 7.79 (s, 1 H, Ar). 3e: 1H NMR (CDCl3)
ꢂ ¼ 2:43 (Me), 2.60 (Me), 3.99 (OMe), 4.01 (OMe), 7.04 (br
s, Ar-H), 7.06 (br s, Ar), 7.16 (br s, Ar), 7.34 (br s, Ar).
R. D. Haworth and J. R. Atkinson, J. Chem. Soc., 1938, 767.
Scheme 5.
A tentative mechanistic rationalization for the observed
novel benzoannelation involves the initial attack of 1 with
TMSOTf. The oxonium ion intermediate (9) thus formed was
further attacked by a base to give diene (10). Rearrangement of 10
followed by proton abstraction gave an exomethylene compound
(11), which finally produced naphthalene, 3 (Scheme 6).
We are currently continuing further investigation on the
reaction and synthetic application of these compounds.
9
References and Notes
1
R. W. Alde, P. S. Bowman, W. R. Steele, and D. R.