626
A. Srikrishna et al. / Tetrahedron: Asymmetry 19 (2008) 624–627
1.6 mL, 3.85 mmol) over a period of 5 min and stirred for
20 min at the same temperature. To LDA thus formed
was added dropwise a solution of ester 10 (200 mg,
1.1 mmol) in anhydrous THF (2 mL) over a period of
5 min and stirred for 1 h. A solution of PhSeCl (253 mg,
1.32 mmol) in anhydrous THF (1 mL) was added to the
reaction mixture and stirred for 1.5 h at the same tempera-
ture and then for 10 h at rt. Saturated aq NH4Cl (10 mL)
was added to the reaction mixture and extracted with ether
(2 ꢂ 7 mL). The combined organic layer was washed with
brine (10 mL) and dried over Na2SO4. Solvent was evapo-
rated under reduced pressure. The residue was taken in
CH2Cl2 (2 mL) and 30% aq H2O2 (5 mL) and pyridine
(0.3 mL) were added, and stirred at ice temperature for
3 h. The reaction mixture was then diluted with water
(5 mL) and extracted with CH2Cl2 (2 ꢂ 5 mL). The com-
bined organic extract was washed with brine (5 mL) and
dried over Na2SO4. Evaporation of the solvent and purifi-
cation of the residue on a silica gel column using CH2Cl2–
CDCl3 + CCl4): d 7.28 (2H, d, J 8.1 Hz) and 7.08 (2H, d,
J 8.1 Hz) [Ar-H], 2.33 (3H, s, Ar-CH3), 2.44–2.26 (1H,
m), 2.05–1.70 (3H, m), 1.60–1.50 (2H, m), 0.93 (3H, d, J
5.4 Hz, sec-CH3), 0.92 (3H, s) and 0.50 (3H, s) [2 ꢂ tert-
CH3]; 13C NMR (100 MHz, CDCl3 + CCl4): d 143.0 (C),
136.0 (C), 128.1 (2C, CH), 126.6 (2C, CH), 86.0 (C, C-1),
46.6 (C, C-2), 41.2 (CH, C-3), 38.0 (CH2, C-5), 29.9
(CH2, C-4), 25.8 (CH3), 21.0 (CH3), 17.5 (CH3), 16.6
(CH3); HRMS m/z: (M+Na) calcd for C15H22ONa,
241.1568; found, 241.1576.
4.4. (3S)-1-(4-Methylphenyl)-2,2,3-trimethylcyclopentene 2
(laurokamurene B)
To a magnetically stirred solution of tertiary alcohol 11
(18 mg, 0.09 mmol) in CH2Cl2 (1 mL) was added PTSA
(10 mg) and stirred for 1.5 h at room temperature. It was
then quenched with saturated aq NaHCO3 (2 mL) and ex-
tracted with CH2Cl2 (2 ꢂ 2 mL). The CH2Cl2 extract was
washed with brine (5 mL) and dried (Na2SO4). Evapora-
tion of the solvent and purification of the residue over a sil-
hexane (1:9) as eluent furnished a,b-unsaturated ester 8
24
(156 mg, 79%) as an oil. ½aꢁD ¼ ꢀ7:5 (c 4.6, CHCl3); IR
(neat): mmax/cmꢀ1 2956, 2872, 1724, 1652, 1456, 1435,
1388, 1376, 1360, 1234, 1194, 1170, 1026, 896, 862; 1H
NMR (400 MHz, CDCl3 + CCl4): d 5.71 (1H, s, H-2),
3.66 (3H, s, OCH3), 2.52–2.40 (2H, m), 1.80–1.68 (3H,
m), 1.30 (3H, s) and 1.07 (3H, s) [2 ꢂ tert-CH3], 0.93
(3H, d, J 6.6 Hz, sec-CH3); 13C NMR (100 MHz,
CDCl3 + CCl4): d 175.0 (C, OC@O), 165.7 (C, C-10),
112.2 (CH, C-2), 50.7 (CH3, OCH3), 47.3 (CH, C-30),
44.8 (C, C-20), 36.0 (CH2), 30.4 (CH2), 24.2 (CH3), 18.8
(CH3), 13.6 (CH3); HRMS m/z: (M+H) calcd for
C11H19O2, 183.1385; found, 183.1385.
ica gel column using hexane as eluent furnished
22
laurokamurene B 2 (14 mg, 85%) as an oil. ½aꢁD ¼ þ14:0
24
(c 1.2, CHCl3) {lit.2 ½aꢁD ¼ þ10:0 (c 0.09, CHCl3)}; IR
(neat): mmax/cmꢀ1 3043, 3025, 2958, 2924, 2869, 2835,
1
1612, 1564, 1510, 1466, 1455, 1384, 1372, 1361, 805; H
NMR (300 MHz, CDCl3): d 7.17 (2H, d, J 8.1 Hz) and
7.07 (2H, d, J 8.1 Hz) [Ar-H], 5.67 (1H, br s, H-5), 2.33
(3H, s, Ar-CH3), 2.45–2.30 (1H, m), 2.03–1.93 (2H, m),
1.08 (3H, s, tert-CH3), 1.00 (3H, d, J 6.6 Hz, sec-CH3),
0.97 (3H, s, tert-CH3).
4.3. (1R,3S)-1-(4-Methylphenyl)-2,2,3-trimethylcyclo-
pentan-1-ol 11
Acknowledgements
We thank the Department of Science and Technology,
New Delhi for the financial support, Indian Institute of Sci-
ence and University Grants Commission, New Delhi for
the award of research fellowships to B.B. and R.R.B. We
are grateful to M/s Organica Aromatics (Bangalore) Pvt.
Ltd, for the generous gift of campholenaldehyde.
Dry ozone in oxygen was passed through a cold (ꢀ70 °C)
solution of ester 8 (143 mg, 0.79 mmol) and a catalytic
amount of NaHCO3 (15 mg) in 1:4 MeOH–CH2Cl2
(10 mL) until it turned blue. Excess ozone was purged with
oxygen. Me2S (0.66 mL, 7.9 mmol) was added to the reac-
tion mixture and stirred for 8 h at rt. Water (7 mL) was
added to the reaction mixture and extracted with CH2Cl2
(2 ꢂ 5 mL). The combined organic extract was washed
with brine (10 mL) and dried over Na2SO4. Evaporation
of the solvent furnished ketone 7, which was used without
further purification.7 To a suspension of Li (35 mg,
5.0 mmol) in anhydrous THF (1 mL) in a round bottom
flask, placed in an ultrasonic cleaning bath, was added a
solution of ketone 7 obtained above, and 4-bromotoluene
(0.62 mL, 5.0 mmol) in anhydrous THF (3 mL) and the
reaction mixture was sonochemically irradiated for 1 h.
The reaction mixture was decanted from excess lithium,
and quenched with saturated aqueous NH4Cl (5 mL) and
extracted with ether (2 ꢂ 5 mL). The ether layer was
washed with brine (10 mL) and dried over Na2SO4. Evap-
oration of the solvent and purification of the residue over a
silica gel column using CH2Cl2–hexane (1:3) as eluent
References
1. Martin, J. D.; Darias, J. In Marine Natural Products; Scheuer,
P. J., Ed.; Academic Press: New York, 1978; Vol. I, pp 151–
161.
2. Mao, S.-C.; Guo, Y.-W. J. Nat. Prod. 2006, 69, 1209–1211.
3. Mao, S.-C.; Guo, Y.-W. Chin. Tradit. Herb. Drugs 2004, 35, 8–17.
4. Srikrishna, A.; Khan, I. A.; Babu, R. R.; Sajjanshetty, A.
Tetrahedron 2007, 63, 12616–12620.
5. Liu, H.-J.; Chan, W. H. Can. J. Chem. 1982, 60, 1081–1091.
6. For confirming the structure of ester 10, it was converted into
the crystalline derivative 12. Thus, the reduction of ester 10
with LAH followed by coupling of the resulting primary
alcohol with 3,5-dinitrobenzoic acid using DCC and DMAP
furnished dinitrobenzoate 12, which was recrystallized from
methanol at room temperature. Mp 55–57 °C; selected spectra
23
furnished the tertiary alcohol 11 (103 mg, 60% for two
data for ester 12; ½aꢁD ¼ ꢀ10:5 (c 2.6, CHCl3); IR (neat): mmax
/
23
cmꢀ1 3104, 2956, 2871, 1732, 1630, 1549, 1463, 1345, 1280,
1167, 921, 730; 1H NMR (400 MHz, CDCl3 + CCl4): d 9.21
(1H, t, J 2.1 Hz) and 9.14 (2H, d, J 2.1 Hz) [Ar-H], 4.50–4.35
steps) as an oil. ½aꢁD ¼ þ10:7 (c 1.4, CHCl3); IR (neat):
m
max/cmꢀ1 3487, 3025, 2961, 2873, 1512, 1456, 1385,
1368, 1110, 1009, 815; 1H NMR (400 MHz,