References
1a
Yamamura S.
Shizuri Y.
Shigemori H.
Okuno Y.
Ohkubo M.
Tetrahedron
1991,
47:
635
1b
Mander LN.
Chem. Rev.
1992,
92:
573
1c
Engler TA.
Wei DD.
Letavic MA.
Tetrahedron Lett.
1993,
34:
1429
1d
Nakajima H.
Isomi K.
Hamasaki T.
Ichinoe M.
Tetrahedron Lett.
1994,
35:
9597
1e
Heathcock CH.
Graham SL.
Pirrung MC.
Plavac F.
White CT.
The Total Synthesis
of Natural Products
Vol. 5:
Apsimon JW.
Wiley;
New York:
1982.
2
Snider BB.
Cole BM.
J. Org. Chem.
1995,
60:
5376
3a
Evans EH.
Hewson AT.
March LA.
Nowell IW.
Wadsworth AH.
J.
Chem. Soc., Perkin Trans. 1
1987,
137
3b
Evans EH.
Hewson AT.
March LA.
Nowell IW.
J.
Chem. Soc., Chem. Commun.
1982,
1342
4a
Ouvrard N.
Ouvrard P.
Rodriguez J.
Santelli M.
J. Chem.
Soc., Chem. Commun.
1993,
571
4b
Filippini M.-H.
Faure R.
Rodriguez J.
J.
Org. Chem.
1995,
60:
6872
5
Dauben WC.
Bunce RA.
J. Org. Chem.
1983,
48:
4642
6
Kim JN.
Im YJ.
Kim JM.
Tetrahedron
Lett.
2002,
43:
6597
7a
Barun O.
Nandi S.
Panda K.
Ila H.
Junjappa H.
J. Org.
Chem.
2002,
67:
5398
7b
Gascoyne DG.
Finkbeiner HL.
Chan KP.
Gordon JL.
Stewart KR.
Kazlauskas RJ.
J. Org. Chem.
2001,
66:
3041
7c
Chiba K.
Uchiyama R.
Kim S.
Kitano Y.
Tada M.
Org. Lett.
2001,
3:
1245
7d
Pati LC.
Rpy A.
Mukherjee D.
Tetrahedron Lett.
2000,
41:
10353
8 Synthesis of 3a and 4a (typical procedure): To a stirred mixture
of Baylis-Hillman acetate 1a (109
mg, 0.5 mmol) and ethyl 2-oxocyclopentanecarboxylate (78 mg, 0.5
mmol) in ethanol (3 mL) was added K2CO3 (76
mg, 0.55 mmol) and stirred at room temperature for 22 h. After the
usual workup process and column chromatographic purification (hexane/diethyl
ether = 4:1) desired products 3a (24
mg, 15%) and 4a (E,
91 mg, 58%) were obtained as clear oils. During separation Z-form of 4a was
isolated also (20 mg, 13%). Selected data of prepared compounds
are as follows. 3a: 1H NMR
(CDCl3) δ 1.13 (t, J = 7.2
Hz, 3 H), 1.65-1.82 (m, 3 H), 2.14-2.38 (m, 3
H), 2.45 (s, 3 H), 2.98 (d, J = 14.2
Hz, 1 H), 3.38 (d, J = 14.2
Hz, 1 H), 3.88-4.04 (m, 2 H), 7.30-7.42 (m, 5
H), 7.58 (s, 1 H). 4a (E-form): 1H
NMR (CDCl3) δ 1.26 (t, J = 7.1
Hz, 3 H), 1.46 (s, 3 H), 1.59-1.67 (m, 1 H), 1.85-1.95
(m, 2 H), 2.34 (s, 1 H, OH), 2.35-2.41 (m, 1 H), 2.43-2.45
(m, 1 H), 2.75 (dt, J = 15.2
Hz and 2.2 Hz, 1 H), 3.08 (d, J = 15.2
Hz, 1 H), 4.19 (q, J = 7.1 Hz,
2 H), 7.09 (d, J = 2.2 Hz, 1
H), 7.21-7.38 (m, 5 H); 13C
NMR (CDCl3) δ 14.10, 18.09, 26.19, 27.81, 35.44,
57.53, 58.32, 61.37, 78.72, 126.96, 127.58, 128.28, 129.20, 136.58,
139.15, 170.67, 209.50; CIMS m/z (rel. intensity) 75 (100), 83 (70),
157 (54), 173 (57), 201 (45), 219 (60), 269 (51), 297 (42), 315
(M+ + 1, 75). 4a (Z-form): 1H NMR (CDCl3) δ 1.25
(t, J = 7.2 Hz, 3 H), 1.59 (s,
3 H), 1.50-2.00 (m, 3 H), 2.19 (br s, 1 H), 2.34-2.45
(m, 2 H), 3.05 (d, J = 14.4
Hz, 1 H), 3.23 (dt, J = 14.4 Hz
and 2.1 Hz, 1 H), 4.18 (qd, J = 7.2
Hz and 1.3 Hz, 2 H), 6.82 (d, J = 1.9
Hz, 1 H), 7.21-7.40 (m, 5 H); 13C
NMR (CDCl3) δ 14.17, 19.51, 25.08, 26.15, 37.18,
56.96, 57.13, 61.35, 81.64, 127.30, 128.41, 128.96, 129.19, 136.45, 138.05,
170.73, 209.94.
Synthesis of 5a and 6a (typical procedure): To a stirred mixture
of Baylis-Hillman acetate 1a (153
mg, 0.7 mmol) and ethyl 2-oxocyclopentanecarboxylate (110 mg, 0.7 mmol)
in ethanol (3 mL) was added K2CO3 (110 mg,
0.8 mmol) and heated to reflux for 1 h. After the usual workup process
and column chromatographic purification (hexane/ethyl acetate = 4:1)
desired products 5a (90 mg, 41%)
and 6a (48 mg, 23%) were obtained
as clear oils. Selected data of prepared compounds are as follows. 5a: 1H NMR (CDCl3) δ 1.05
(t, J = 7.1 Hz, 3 H), 1.66-1.96
(m, 5 H), 2.35-2.42 (m, 1 H), 2.71 (dd, J = 15.8
Hz and 2.0 Hz, 1 H), 2.90 and 2.95 (2 d, J = 16.5
Hz, 1 H each, C=C-CH2), 3.46 (dd, J = 15.8 Hz and 1.4 Hz, 1 H),
4.06 (q, J = 7.1 Hz, 2 H), 7.27-7.44
(m, 5 H), 7.59 (s, 1 H); 13C NMR (CDCl3) δ 13.83,
21.09, 33.43, 35.49, 40.16, 50.01, 56.21, 61.23, 81.23, 128.49,
128.79, 129.87, 132.99, 135.03, 136.84, 175.50, 199.32; CIMS m/z (rel. intensity) 117 (19),
269 (15), 297 (100), 315 (M++1, 2). 6a: 1H NMR (CDCl3) δ 1.02
(t, J = 7.1 Hz, 3 H), 1.68-2.82 (m,
6 H), 2.55 (dd, J = 14.4 Hz
and 2.8 Hz, 1 H), 3.87 (d,
J = 14.4
Hz, 1 H), 3.99 (q, J = 7.1 Hz,
2 H), 6.19 (t, J = 2.0 Hz, 1
H), 7.21-7.45 (m, 5 H), 7.65 (d, J = 2.8
Hz, 1H);
13C NMR (CDCl3) δ 13.85,
22.58, 31.91, 37.08, 38.12, 54.74, 61.41, 124.16, 128.34, 128.41,
129.45, 131.95, 135.64, 136.03, 168.47, 173.05, 186.16; EIMS (70
eV) m/z (rel.
intensity) 115 (79), 165 (77), 195 (41), 223 (96), 295 (100), 296
(M+, 84).
9 The reaction of the bicyclic compound 4a in ethanol in the presence of K2CO3 (1.1
equiv) at reflux temperature for 30 min gave the thermodynamic products 5a (36%) and 6a (20%).
10a
Kim JN.
Jung YM.
Im YJ.
Tetrahedron Lett.
2002,
43:
6209
10b
Im YJ.
Lee KY.
Kim TH.
Kim JN.
Tetrahedron Lett.
2002,
43:
4675
10c
Kim JN.
Lee HJ.
Gong JH.
Tetrahedron Lett.
2002,
43:
9141
10d
Lee KY.
Kim JM.
Kim JN.
Tetrahedron
2003,
59:
385
11 The stereochemistry of 4a was
confirmed by NOE experiments (Figure
[1]
).
The stereochemistry between the methyl group at C-2 position and
the proton at C-1 position might be cis relationship.
