Zeolite-Induced Heterodomino Reaction. Regioselective Synthesis of 2H-1-Benzopyrans from Phenols and α-Alkynols

Full text of DOI:10.1021/jo970690y

7024
J . Org. Chem. 1997, 62, 7024-7027
Sch em e 1
Zeolite-In d u ced Heter od om in o Rea ction .
Regioselective Syn th esis of
2H-1-Ben zop yr a n s fr om P h en ols a n d
r-Alk yn ols
Franca Bigi, Silvia Carloni, Raimondo Maggi,
Chiara Muchetti, and Giovanni Sartori*
Dipartimento di Chimica Organica e Industriale
dell’Universita`, Viale delle Scienze, I-43100 Parma, Italy
Received April 16, 1997
In tr od u ction
The development of “one-pot reactions” represents a
great challenge in organic synthesis today. Indeed this
strategy allows the construction of highly complex mol-
ecules from relatively simple reagents under economically
favorable conditions. Moreover the combination of the
“one-pot strategy” with the use of environmentally friendly
solid acid catalysts is now the best tool for preparation
of specific target compounds with minimum production
of pollutants as well as reduction of the cost.1
Sch em e 2
As part of a program designed to develop new selective
and preparatively useful methodologies based on the use
of solid acids as promoters for fine chemicals preparation,
previous studies from these laboratories have described
the rearrangement-dehydration of R-alkynols to R,â-
unsaturated ketones or conjugated enynes over zeolite
catalyst.2 Thus, heating a slurry of zeolite HSZ-3603 and
R-alkynols 1 at 130 °C in chlorobenzene led to R,â-
unsaturated ketones 2 or conjugated enynes 3 depending
on R and R1 being alkyl or aryl groups (Scheme 1).
In light of these results it was thought that enynes 3
produced from R-alkynols 1 would offer the potential for
subsequent bisalkylation of phenol substrates leading to
the construction of 2H-1-benzopyrans 5 with proper
regiochemical control (Scheme 2, route A) following a
chemical behavior similar to that previously observed
with conjugated dienes4 (Scheme 2, route B).
We have thus reinvestigated this reaction under zeolite
catalysis. Here we show the results of these studies.
The 2H-1-benzopyran ring system constitutes the basic
skeleton of a variety of natural compounds showing
interesting biological activities. Different synthetic ap-
proaches to these compounds are reported in the litera-
ture, including addition of Grignard reagents to cou-
marins and chromanones, Dieckmann and aldol-type
condensation of convenient aromatic carbonyl compounds
or thermal rearrangement of propargyl phenyl ethers.5
Acid-catalyzed reaction of phenols with R-alkynols was
also attempted, but yields reported are less than 10%.6
Resu lts a n d Discu ssion
We have first pursued evidence for the feasibility and
the regioselective control of the reaction of enynes with
phenols under solid acid catalysis. Indeed, although
many examples of bisalkylation of phenols with dienes
to produce chromans or benzofurans are known,7 to the
best of our knowledge the same reaction with enynes was
not reported.
Treatment of p-methoxyphenol (4c) with 3-phenyl-3-
buten-1-yne (3x) in the presence of zeolite HSZ-360
[commercial faujasitic-type zeolite with 13.9 SiO2/Al2O3
molar ratio, pore size 8 Å, surface area 500 ( 10 m2/g8,
and acidity 0.51 mequiv H+/g9] in chlorobenzene at reflux
(1) (a) Tietze, L. F.; Beifuss, U. Angew. Chem., Int. Ed. Engl. 1993,
32, 131. (b) Grigg, R.; Sridharan, V. Comprehensive Organometallic
Chemistry; 2nd ed.; Abel, E., Wikinson, G., Stone, F. G. A., Eds.,
Pergamon Press: New York, 1995; Vol. 12, Chapter 3,6. (c) Padua, A.
Chem. Rev. 1996, 96, 223. (d) Grigg, R.; Putnikovic, B.; Urch, C.
Tetrahedron Lett. 1996, 37, 695. (e) Grigg, R.; Sridharan, V.; Terrier,
C. Tetrahedron Lett. 1996, 37, 4221. (f) Negishi, E.; Coperet, C.; Ma,
S.; Liou, S. Y.; Liu, F. Chem. Rev. 1996, 96, 365. (g) Denmark, S. E.;
Senanayake, C. B. W. Tetrahedron, 1996, 52, 11579.
(2) Sartori, G.; Pastorio, A.; Maggi, R.; Bigi, F. Tetrahedron 1996,
52, 8287.
(3) HSZ-360 acidic zeolite was purchased by Tosoh Corp.
(4) Bolzoni, L.; Casiraghi, G.; Casnati, G.; Sartori, G. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 684.
(6) (a) Cardillo, G.; Merlini, L. Gazz. Chim. Ital. 1968, 98, 191 (Chem.
Abstr. 1968, 69, 43735k). (b) Hoffman, F. Br. Patent 877,960, 1960
(Chem. Abstr. 1962, 56, 7282). (c) Pendse, H.; Ruegg, R.; Ryser, G. U.S.
Patent 3,004,040, 1960 (Chem. Abstr. 1962, 56, 8693d).
(7) (a) Dauben, W. G.; Cogen, J . M.; Behar, V. Tetrahedron Lett.
1990, 31, 3241. (b) Pochini, A.; Marchelli, R.; Bocchi, V. Gazz. Chim.
Ital. 1975, 195, 1245. (c) Mohamed, S. E. N.; Thomas, P.; Whiting, D.
A. J . Chem. Soc., Chem. Commun. 1983, 738. (d) Laan, J . A. M.; Geisen,
F. L. L.; Ward, J . P. Chem. Ind. 1989, 354. (e) Wehrli, P. A.; Fryer, R.
I.; Metlesics, W. J . Org. Chem. 1971, 36, 2910. (f) Molyneux, R. J .;
J urd, L. Tetrahedron 1970, 26, 4743.
(5) (a) Schweizer, E. E.; Meeder-Nycz, D. 2H- and 4H-1-Benzopyr-
ans. In Heterocyclic Compounds. Chromenes, Chromanones and
Chromanes, Ellis, G. P., Ed., J ohn Wiley and Sons: NY, 1977; pp 11-
139. (b) North, J . T.; Kronenthal, D. R.; Pullockaran, A. J .; Real, S.
D.; Chen, H. Y. J . Org. Chem. 1995, 60, 3397.
(8) Determined in our laboratory by the BET method: Brunauer,
S.; Emmett, P. H.; Teller, E. J . Am. Chem. Soc. 1938, 60, 309.
S0022-3263(97)00690-7 CCC: $14.00 © 1997 American Chemical Society

Notes
J . Org. Chem., Vol. 62, No. 20, 1997 7025
Ta ble 1. Syn th esis of som e 2H-1-Ben zop yr a n s 5
entry
R
R1
R2
R3
R4
R5
product
yield (%)
selectivity (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
CH3
CH3
CH3
CH3
C6H5
C6H5
H
H
H
H
H
H
H
C6H5
C6H5
C6H5
C6H5
CH3
CH3
H
H
H
H
H
OH
OCH3
H
H
H
H
H
H
H
H
5a x
5bx
5cx
5d x
5ex
5fx
5gx
5cy
5ey
5fy
40
75
60
50
75
66
50
70
60
65
25
70
60
90
95
90
85
95
95
85
90
95
94
95
98
90
-OCH2O-
-CH)CHCH)CH-
H
CH3
H
-CH)CHCH)CH-
H
CH3
H
H
H
H
OH
OCH3
-CH)CHCH)CH-
CH3
H
CH3
H
H
H
H
-CH)CHCH)CH-
CH3
H
OH
OCH3
H3
CH3
H
H
5gy
5cz
5h z
OCH3
for 3 h afforded the expected product 5cx in 65% yield
and 92% selectivity. Further experiments performed in
the absence of any catalyst gave no reaction; use of Lewis
acids (previously utilized in similar reactions with dienes)7
gave mixtures of products.
The reaction could be carried out in a more rapid
fashion by using 3-phenyl-1-butyn-3-ol (1x), the precursor
of 3x, with only a slight decrease in efficiency (60% yield,
90% selectivity) (Table 1, entry 3).
To investigate the generality of this process, the
R-alkynols 1x-z and phenols 4a -h were subjected to
similar reaction conditions allowing the easy synthesis
of 2H-1-benzopyrans 5a x-h z (Table 1).
The key step of the present process is a typical
electrophilic substitution, since the presence of electron-
donating groups on the phenol ring results in a more
facile and more efficient production of compounds 5
(Table 1, entries 2-5). However, the process suffers from
some steric hindrance. Indeed, trimethyl hydroquinone
(4g) reacts with 3-phenyl-1-butyn-3-ol (1x) [R′ ) H],
affording the product 5gx in 50% yield, whereas the
reaction with 3-methyl-1-phenyl-1-butyn-3-ol (1y) [R′ )
C6H5] produces compound 5gy in 25% yield (Table 1,
entries 7 and 11).
The regiochemical outcome of the present reaction
appears to be the same with all R-alkynols and phenols
utilized since in all cases the sole products arise from
interaction of the phenol oxygen with the olefinic double
bond and the ortho-carbon of the phenol ring with the
acetylenic framework of the enyne intermediate.10 The
process shows also complete ortho-regiospecificity with
respect to the phenol ring (Table 1, entry 1).
To this purpose we studied the reaction of p-methoxy-
phenol (4c) with R-alkynols 1v (R ) CH3, R1 ) H) and
1w (R ) C2H5, R1 ) CH3) which in the presence of zeolite
HSZ gave R,â-unsaturated ketones 2v and 2w instead
of conjugated enynes via a Rupe rearrangement.2 Under
the conditions used in the previous experiments, com-
pounds 2v and 2w were recovered in 40% and 62% yield,
respectively, as the sole products. Guided by these
results and previous studies from literature,12 we envis-
aged two possible modes by which the enyne might react
with the phenol: a direct attack of the carbon-carbon
triple bond on the ortho-position of the aromatic ring
(Scheme 3, route A) or prior aryl propargyl ether forma-
tion followed by a Claisen-like rearrangement (Scheme
3, route B). However we argue against the last formula-
tion, because attempts to isolate the aryl propargyl ether
in the reaction of 2,4,6-trimethylphenol (4i) with 3-phen-
yl-1-butyn-3-ol (1x) resulted in the complete recovering
of 4i accompanied by 3-phenyl-3-buten-1-yne (3x) in 92%
yield.13
The moderately acidic zeolite HSZ-360 first promotes
the dehydration of 1 to 3, which then regioselectively
adds to the phenol substrate 4 to yield dienic compound
7; further isomerization of 7 to tautomers 8 or 9 followed
by an electrocyclic rearrangement affords the target
compound 5, in agreement with previously reported
studies.12
In conclusion, zeolite HSZ-360 allows both dehydration
of R-alkynols to conjugated enynes and their successive
regiospecific reaction with phenols, giving 2H-1-benzopy-
rans in good yields with a minimum number of synthetic
steps according to a typical heterodomino process.14
On the basis of our previous studies concerning the
dehydration of R-alkynols to conjugated enynes2 and the
ortho-regioselective alkenylation of phenols and aromatic
amines with alkynes under zeolite catalysis,11 we believed
that enynes 3 might be the actual alkylating reagents.
Exp er im en ta l Section
Gen er a l. Melting and boiling points are uncorrected. 1H
NMR spectra were recorded at 400 and 300 MHz. Mass spectra
were obtained in EI mode at 70 eV. Microanalyses were carried
(9) Determined in our laboratory by temperature programmed
desorption of ammonia gas (NH3-TPD): Berteau, P.; Delmon, B. Catal.
Today 1989, 5, 121.
(12) (a) Richey, H. G., J r.; Philips, J . C.; Renmick, L. E. J . Am. Chem.
Soc. 1965, 87, 1381. (b) Zsindely, J .; Schmid, H. Helv. Chem. Acta 1968,
51, 1510. (c) Harfenist, M.; Thom, E. J . Org. Chem. 1972, 37, 841. (d)
Rao, U.; Balasubramanian, K. K. Tetrahedron Lett. 1983, 24, 5023.
(e) Tsukayama, M.; Utsumi, H.; Kunugi, A. J . Chem. Soc., Chem.
Commun. 1995, 615.
(13) It is important to emphasize that the rearrangement of aryl
propargyl ethers requires high temperatures (220-240 °C), whereas
the present reaction occurs at 130 °C.
(10) Confirmed by 1H NMR NOESY experiment showing, for
example, a strong cross-peak correlation between the H-5 naphtholic
hydrogen and the H-4 olefinic hydrogen in compound 5fx.
(11) (a) Sartori, G.; Bigi, F.; Pastorio, A.; Porta, C.; Arienti, A.;
Maggi, R.; Moretti, N.; Gnappi, G. Tetrahedron Lett. 1995, 50, 9177.
(b) Arienti, A.; Bigi, F.; Maggi, R.; Marzi, E.; Moggi, P.; Rastelli, M.;
Sartori, G.; Tarantola, F. Tetrahedron 1997, 53, 3795.
(14) Tietze, L. F. Chem. Rev. 1996, 96, 115.

7026 J . Org. Chem., Vol. 62, No. 20, 1997
Notes
(23), 223 (100), 161 (26). Anal. Calcd for C16H14O2: C, 80.7; H,
5.9. Found: C, 80.9; H, 6.2.
Sch em e 3
6-Met h oxy-2-m et h yl-2-p h en yl-2H -1-b en zop yr a n (5cx):
yield 1.5 g (60%), pale yellow liquid; bp 113-115 °C/0.05 mmHg;
1H NMR (300 MHz, CDCl3) δ 7.51 (2 H, d, J ) 7.5 Hz), 7.32 (2
H, t, J ) 7.5 Hz), 7.25 (1 H, t, J ) 7.5 Hz), 6.83 (1 H, d, J ) 8.7
Hz), 6.69 (1 H, dd, J ) 8.7 and 3.0 Hz), 6.55 (1 H, d, J ) 3.0
Hz), 6.43 (1 H, d, J ) 9.7 Hz), 5.99 (1 H, d, J ) 9.7 Hz), 3.74 (3
H, s), 1.77 (3 H, s); MS m/ z (M+) 252 (21), 237 (100), 175 (19).
Anal. Calcd for C17H16O2: C, 80.9; H, 6.4. Found: C, 80.7; H,
6.3.
2-Meth yl-6,7-(m eth ylen ed ioxy)-2-p h en yl-2H-1-ben zop y-
r a n (5d x): yield 1.3 g (50%), pale yellow solid; mp 58-59 °C
(Et2O); 1H NMR (300 MHz, CDCl3) δ 7.45 (2 H, dm, J ) 7.1
Hz), 7.25 (2 H, tm, J ) 7.1 Hz), 7.15 (1 H, tt, J ) 7.1 and 2.3
Hz), 6.46 (1 H, s), 6.38 (1 H, s), 6.25 (1 H, d, J ) 9.7 Hz), 5.75 (1
H, d, J ) 9.7 Hz), 5.70 (1 H, d, J ) 11.6 Hz), 5.69 (1 H, d, J )
11.6 Hz), 1.69 (3 H, s); MS m/ z (M+) 266 (17), 251 (100), 189
(15). Anal. Calcd for C17H14O3: C, 76.7; H, 5.3. Found: C, 76.9;
H, 5.2.
3-Meth yl-3-p h en yl-3H-n a p h th o[2,3-b]p yr a n (5ex): yield
2.0 g (75%), pale orange liquid; bp 75-78 °C/0.05 mmHg; 1H
NMR (300 MHz, CDCl3) δ 8.09 (1 H, d, J ) 8.2 Hz), 7.89 (1 H,
d, J ) 8.2 Hz), 7.84 (1 H, d, J ) 8.2 Hz), 7.8-7.7 (2 H, m), 7.62
(1 H, ddd, J ) 8.3, 7.0 and 1.3 Hz), 7.6-7.4 (4 H, m), 7.41 (1 H,
d, J ) 8.8 Hz), 7.32 (1 H, d, J ) 9.9 Hz), 6.21 (1 H, d, J ) 9.9
Hz), 2.04 (3 H, s); MS m/ z (M+) 272 (17), 257 (100), 195 (38),
128 (24). Anal. Calcd for C20H16O: C, 88.2; H, 5.9. Found: C,
88.0; H, 6.2.
2-Meth yl-2-p h en yl-2H-n a p h th o[1,2-b]p yr a n (5fx): yield
1.8 g (66%), pale orange liquid; bp 80-82 °C/0.05 mmHg; 1H
NMR (300 MHz, CDCl3) δ 8.32 (1 H, d, J ) 8.0 Hz), 7.72 (1 H,
d, J ) 8.0 Hz), 7.55 (2 H, d, J ) 7.8 Hz), 7.5-7.2 (5 H, m), 7.20
(1 H, tm, J ) 7.2 Hz), 7.11 (1 H, d, J ) 8.3 Hz), 6.55 (1 H, d, J
) 9.7 Hz), 5.97 (1 H, d, J ) 9.7 Hz), 1.87 (3 H, s); MS m/ z (M+)
272 (22), 257 (100), 195 (18). Anal. Calcd for C20H16O: C, 88.2;
H, 5.9. Found: C, 88.1; H, 6.0.
out by Dipartimento di Chimica Generale ed Inorganica, Chimica
Analitica, Chimica Fisica dell’Universita` di Parma, Italy. TLC
analyses were performed on Merck 60 PF254 silica gel plates
using mixtures of hexane-ethyl acetate (5-25%). The solvents
were dried on 4 Å molecular sieves. All the reagents were of
commercial quality from freshly opened containers. Zeolite HSZ-
360 (Tosoh Corp.) was utilized without previous thermal or
chemical treatment.
Syn th esis of r-a lk yn ols 1. Gen er a l P r oced u r e. The
R-alkynols were synthesized as reported in the literature starting
from convenient acetylenic compounds (100 mmol) and ketones
(100 mmol).15
6-Hyd r oxy-2,5,7,8-tetr a m eth yl-2-p h en yl-2H-1-ben zop y-
r a n (5gx): yield 1.4 g (50%), pale brown liquid; bp 116-118
1
°C/0.05 mmHg; H NMR (300 MHz, CDCl3) δ 7.48 (2 H, d, J )
7.3 Hz), 7.29 (2 H, t, J ) 7.3 Hz), 7.20 (1 H, tm, J ) 7.3 Hz),
6.65 (1 H, d, J ) 10.1 Hz), 6.00 (1 H, d, J ) 10.1 Hz), 4.18 (1 H,
s), 2.23 (3 H, s), 2.14 (6 H, s), 1.72 (3 H, s); IR (NaCl) 3432 cm-1
;
MS m/ z (M+) 280 (40), 235 (91), 207 (100). Anal. Calcd for
C
19H20O2: C, 81.4; H, 7.2. Found: C, 81.6; H, 7.2.
3-Meth yl-1-p h en yl-1-bu tyn -3-ol (1y): yield 15.9 g (99%),
pale yellow solid; mp 53-54 °C (Et2O); 1H NMR (300 MHz,
CDCl3) δ 7.5-7.2 (5 H, m), 2.2 (1 H, br s), 1.61 (6 H, s); IR (KBr)
3278, 2320 cm-1; MS m/ z (M+) 160 (23), 145 (30), 115 (18). Anal.
Calcd for C11H12O: C, 82.5; H, 7.6. Found: C, 82.3; H, 7.8.
2-P h en yl-3-bu tyn -2-ol (1z): yield 14.4 g (90%), white solid,
mp 41-42 °C (lit.2 mp 41-42.5 °C).
6-Meth oxy-2,2-dim eth yl-4-ph en yl-2H-1-ben zopyr an (5cy):
yield 1.9 g (70%), yellow liquid; bp 83-86 °C/0.05 mmHg; 1H
NMR (300 MHz, CDCl3) δ 7.6-7.1 (5 H, m), 6.82 (1 H, d, J )
8.7 Hz), 6.71 (1 H, dd, J ) 8.7 and 3.0 Hz), 6.57 (1 H, d, J ) 3.0
Hz), 5.64 (1 H, s), 3.66 (3 H, s), 1.43 (6 H, s); MS m/ z (M+) 266
(11), 251 (100). Anal. Calcd for C18H18O2: C, 81.2; H, 6.8.
Found: C, 81.4; H, 6.7.
Syn th esis of 2H-1-Ben zop yr a n s 5. Gen er a l P r oced u r e.
The selected alkynol (10 mmol), the selected phenol (10 mmol),
and zeolite HSZ-360 (1 g) in chlorobenzene (10 mL) were heated
at reflux for 6 h. After cooling to rt, the catalyst was removed
by filtration and washed with diethyl ether (100 mL); the
solvents were distilled off and the crude was chromatographed
on silica gel column with hexane-ethyl acetate mixtures to give
the products.
2-Meth yl-2-p h en yl-2H-1-ben zop yr a n (5a x): yield 0.9 g
(40%), pale yellow liquid; bp 71-73 °C/0.05 mmHg; 1H NMR (300
MHz, CDCl3) δ 7.50 (2 H, d, J ) 7.3 Hz), 7.31 (2 H, t, J ) 7.3
Hz), 7.22 (1 H, t, J ) 7.3 Hz), 7.11 (1 H, td, J ) 7.3 and 1.4 Hz),
6.96 (1 H, dd, J ) 7.3 and 1.4 Hz), 6.87 (1 H, d, J ) 7.3 Hz),
6.81 (1 H, t, J ) 7.3 Hz), 6.44 (1 H, d, J ) 9.8 Hz), 5.91 (1 H, d,
J ) 9.8 Hz), 1.79 (3 H, s); MS m/ z (M+) 222 (10), 207 (100), 145
(25). Anal. Calcd for C16H14O: C, 86.5; H, 6.4. Found: C, 86.7;
H, 6.2.
3,3-Dim et h yl-1-p h en yl-3H -n a p h t h o[2,3-b]p yr a n (5ey):
yield 1.8 g (64%), yellow solid; mp 114-116 °C (Et2O); 1H NMR
(300 MHz, CDCl3) δ 7.70 (2 H, d, J ) 8.6 Hz), 7.4-7.1 (7 H, m),
7.09 (1 H, d, J ) 8.4 Hz), 7.01 (1 H, ddd, J ) 8.0, 6.5 and 1.1
Hz), 5.69 (1 H, s), 1.49 (6 H, s); MS m/ z (M+) 286 (17), 271 (100),
135 (14). Anal. Calcd for C21H18O: C, 88.1; H, 6.3. Found: C,
87.9; H, 6.2.
2,2-Dim et h yl-4-p h en yl-2H -n a p h t h o[1,2-b]p yr a n (5fy):
yield 1.9 g (65%), pale orange oil; bp 165-166 °C/0.05 mmHg;
1H NMR (300 MHz, CDCl3) δ 8.3-7.3 (9 H, m), 7.29 (1 H, d, J
) 8.5 Hz), 7.55 (1 H, d, J ) 8.5 Hz), 5.63 (1 H, s), 1.57 (6 H, s);
MS m/ z (M+) 286 (12), 271 (100). Anal. Calcd for C21H18O: C,
88.1; H, 6.3. Found: C, 88.0; H, 6.5.
6-Hydr oxy-2,2,5,7,8-pen tam eth yl-4-ph en yl-2H-1-ben zopy-
r a n (5gy): yield 0.7 g (25%), pale yellow solid; mp 123-124 °C
1
(Et2O); H NMR (300 MHz, CDCl3) δ 7.4-7.1 (5 H, m), 5.68 (1
H, s), 4.23 (1 H, s), 2.20 (6 H, s), 1.62 (3 H, s), 1.41 (6 H, s); IR
(KBr) 3494 cm-1; MS m/ z (M+) 294 (19), 279 (100). Anal. Calcd
for C20H22O2: C, 81.6; H, 7.5. Found: C, 81.9; H, 7.4.
6-H yd r oxy-2-m et h yl-2-p h en yl-2H -1-b en zop yr a n (5b x):
yield 1.8 g (74%), pale red liquid; bp 100-102 °C/0.05 mmHg;
1H NMR (300 MHz, CDCl3) δ 7.7-7.1 (5 H, m), 6.74 (1 H, d, J
) 8.6 Hz), 6.56 (1 H, dd, J ) 8.6 and 2.9 Hz), 6.44 (1 H, d, J )
2.9 Hz), 6.36 (1 H, d, J ) 9.7 Hz), 5.96 (1 H, d, J ) 9.7 Hz), 4.7
(1 H, br s), 1.74 (3 H, s); IR (NaCl) 3375 cm-1; MS m/ z (M+) 238
6-Meth oxy-2,4-dim eth yl-2-ph en yl-2H-1-ben zopyr an (5cz):
yield 1.9 g (70%), yellow liquid; bp 85-88 °C/0.05 mmHg; 1H
NMR (400 MHz, CDCl3) δ 7.52 (2 H, dd, J ) 7.3 and 1.4 Hz),
7.33 (2 H, t, J ) 7.3 Hz), 7.24 (1 H, tt, J ) 7.3 and 1.4 Hz),
6.9-6.7 (2 H, m), 5.84 (1 H, q, J ) 1.5 Hz), 3.77 (3 H, s), 2.09 (3
H, d, J ) 1.5 Hz), 1.76 (3 H, s); MS m/ z (M+) 266 (10), 251 (100),
(15) Midland, M. M. J . Org. Chem. 1975, 40, 2250.

Notes
J . Org. Chem., Vol. 62, No. 20, 1997 7027
189 (20). Anal. Calcd for C18H18O2: C, 81.2; H, 6.8. Found:
C, 80.9; H, 6.9.
Sintesi e Reattivita` Organica” (ex 40%) and the Con-
siglio Nazionale delle Ricerche (CNR), Italy. The au-
thors are grateful to the Centro Interfacolta` Misure
(CIM) for the use of NMR and mass instruments.
6,7-Dim e t h oxy-2,4-d im e t h yl-2-p h e n yl-2H -1-b e n zop y-
r a n (5h z): yield 1.8 g (60%), pale yellow solid; mp 80-82 °C
1
(Et2O); H NMR (300 MHz, CDCl3) δ 7.6-7.1 (5 H, m), 6.66 (1
H, s), 6.53 (1 H, s), 5.62 (1 H, q, J ) 1.5 Hz), 3.85 (3 H, s), 3.81
(3 H, s), 2.04 (3 H, d, J ) 1.5 Hz), 1.72 (3 H, s); MS m/ z (M+)
296 (15), 281 (100), 219 (30). Anal. Calcd for C19H20O3: C, 77.0;
H, 6.8. Found: C, 76.9; H, 6.6.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR data of all
compounds with peak assignments included (3 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the J ournal and
can be ordered from the ACS; see any current masthead page
for ordering information.
Ack n ow led gm en t. The authors acknowledge the
support of the Ministero dell’Universita` e della Ricerca
Scientifica e Tecnologica (MURST) “Progetto Nazionale
J O970690Y