2048
S. K. Sabui, R. V. Venkateswaran / Tetrahedron Letters 45 (2004) 2047–2048
product 96 was obtained in 55% yield (Scheme 1). The
vinylic olefin protons were retained at d 5.0 and the
newly generated olefinic proton appeared at d 5.56. The
restricted utility of catalyst A when applied to sterically
demanding olefin systems has been observed by others.5
In view of this, we turned to the later version of the
catalyst, catalyst B, which is reported to perform better
in such cases.5 Indeed, when the diene in dichlorome-
thane (0.01M) was stirred for 4.5 h using 5 mol % of the
catalyst, it underwent a clean intramolecular cyclisation
yielding the benzoxepine ester 10,6 in excellent yield
(94%). The presence of a single olefinic proton at d 5.94
attested to the formation of this product and was sup-
ported by subsequent experiments. This olefinic ester
was subjected to quantitative catalytic hydrogenation
furnishing selectively the saturated ester 11,6 together
with traces of the trans isomer (ca. 5%). The desired
major isomer could easily be separated by thin layer
chromatography. This showed spectral features (1H
NMR and 13C NMR) in excellent agreement with those
of the analogous methyl ester, which we had synthesised
earlier.4 Additional confirmation was secured from
interaction of 11 with excess methyl magnesium iodide
to afford the tertiary alcohol 126 (Scheme 2), identical in
all respects with our previous sample,4 which had been
demethylated to heliannuol D.2b
Pcy3
Ru
N Mes
Mes
Cl
Cl
N
Cl
Cl
Ru
Pcy3
Ph
Ph
Pcy3
Catalyst A
Catalyst B
In summary, we describe a very short and facile syn-
thesis of the allelochemical, heliannuol D, employing
ring-closing metathesis to develop the benzoxepane ring
system of 1. The present synthesis furnishes 1 in 6 steps
from the styrenol 6 in a very good overall yield.
Acknowledgements
We gratefully acknowledge financial support from the
Department of Science and Technology, Govt. of India,
New Delhi.
MeO
MeO
i
ii
O
OR
CO2Et
8
6 R = H
7 R = CH CO Et
2
2
References and notes
iii
1. (a) Macias, F. A.; Varela, R. M.; Torres, A.; Molinillo, J.
M. G.; Fronzek, F. R. Tetrahedron Lett. 1993, 34, 1999;
(b) Macias, F. A.; Molinillo, J. M. G.; Varela, R. M.;
Torres, A.; Fronzek, F. R. J. Org. Chem. 1994, 59, 8261;
(c) Macias, F. A.; Varela, R. M.; Torres, A.; Molinillo, J.
M. G. Tetrahedron Lett. 1999, 40, 4725.
OMe
MeO
O
O
CO2Et
CO2Et
2. (a) Grimm, E. L.; Levac, S.; Trimble, L. A. Tetrahedron
Lett. 1994, 35, 6847; (b) Vyvyan, J. R.; Lopper, R. E.
Tetrahedron Lett. 2000, 41, 1151; (c) Takabatke, K.; Nishi,
I.; Shindo, M.; Shishido, K. J. Chem. Soc., Perkin Trans. 1
2000, 1807; (d) Sato, K.; Yoshimura, T.; Shindo, M.;
Shishido, K. J. Org. Chem. 2001, 66, 309; (e) Kishuku, H.;
Shindo, M.; Shishido, K. Chem. Commun. 2003, 350; (f)
Fuminao, D.; Takahisa, O.; Takeshi, S.; Shigeru, N.
Tetrahedron Lett. 2003, 44, 4877; (g) Kamei, T.;
Shindo, M.; Shishido, K. Tetrahedron Lett. 2003, 44,
8505.
9
Scheme 1. Reagents and conditions: (i) K2CO3, BrCH2CO2Et, ace-
tone, reflux, 8 h, 80%; (ii) LDA, THF, )78 °C to rt, CH2@CHCH2Br,
10 h, 78%; (iii) Catalyst A (5 mol %) CH2Cl2, 50 °C, 7 h, 55%.
MeO
MeO
i
ii
CO Et
8
O
O
3. Tuhina, K.; Bhowmik, D. R.; Venkateswaran, R. V.
Chem. Commun. 2002, 634.
CO Et
2
11
2
10
4. Sabui, S. K.; Venkateswaran, R. V. Tetrahedron Lett.
2004, 45, 983.
iii
5. Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 1 8,
and references cited therein.
RO
6. All new compounds reported here gave analytical and
spectral data consistent with the assigned structures.
O
Selected spectral data: For 10: IR 1750 cmÀ1 1H NMR
;
OH
(300 MHz, CDCl3) dH 1.30 (3H, t, J 7.2 Hz), 2.12 (3H, s),
2.19 (3H, s), 2.48 (2H, m), 3.80 (3H, s), 4.22 (2H, q,
12 R = Me
2b
ref.
1
R = H
J
7.2 Hz), 4.88 (1H, dd, J 5.0, 9.7 Hz), 5.94 (1H, t,
J 6.9 Hz), 6.69 (1H, s), 7.04 (1H, s); 13C (CDCl3, 75 MHz)
dC 14.6, 16.3, 22.9, 31.3, 56.1, 61.4, 86.4, 108.9, 123.6, 125.6,
128.8, 131.6, 136.5, 148.5, 154.4, 171.8.
Scheme 2. Reagents and conditions: (i) Catalyst B, (5 mol %), CH2Cl2,
rt, 5 h, 94%. (ii) Pd–C (10%), H2, EtOH, 5 h, 90%; (iii) MeMgI, Et2O,
reflux, 3 h, 96%.