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S. Giese, F. G. West / Tetrahedron 56 (2000) 10221±10228
added in one solid portion. The resulting dark reaction
mixture was stirred vigorously and was allowed to warm
to 0 8C. After 1 h at 08C the reaction was quenched by the
addition of H2O (10 mL). The layers were separated and the
aqueous layer was extracted with CH2Cl2 (10 mL). The
combined organic phases were dried (MgSO4) and concen-
trated under reduced pressure. Puri®cation was achieved by
radial chromatography (silica gel, 2 mm rotor, hexanes/
EtOAc 15:1!12:1) to give 1-phenyl-4-methyl-cyclopent-
3-one 4 (49 mg, 70%) as a clear oil: Rf 0.26 (hexanes/
(dqd, J10.2, 6.9, 1.6 Hz, 1H), 1.12 (d, J7.0 Hz, 3H),
0.78 (d, J7.9 Hz, 3H); 13C NMR (125 MHz, CDCl3) d
219.7, 141.0, 138.3, 129.0, 128.9, 128.4, 127.8, 127.1,
126.7, 53.4, 51.3, 50.4, 47.3, 13.1, 12.7; Anal. Calcd for
C19H20O: C, 86.31; H, 7.64. Found: C, 86.19; H, 7.57.
Triquinane 7b. Rf 0.38 (hexanes/EtOAc 7:1); IR (thin ®lm)
1
1732 cm21; H NMR (500 MHz, CDCl3) d 2.62 (ddd, J
9.1, 9.1, 3.6 Hz, 1H), 2.39±2.34 (m, 1H), 1.94±1.75 (m,
3H), 1.57±1.49 (m, 2H), 1.34 (dddd, J13.0, 6.6, 6.6,
6.6 Hz, 1H); 13C NMR (125 MHz, CDCl3) d 227.2, 52.7,
46.7, 35.1, 30.4, 26.4; Anal. Calcd for C11H16O: C, 80.42; H,
9.84. Found: C, 80.53; H, 9.79.
EtOAc 8:1); IR (thin ®lm) 1708 cm21
;
1H NMR
(300 MHz, CDCl3) d 7.35±7.22 (m, 4H), 7.15±7.12 (m,
2H), 4.03 (dddq, J6.8, 2.4, 2.4, 2.4 Hz, 1H), 2.93 (dd,
J19.0, 6.8 Hz, 1H), 2.35 (dd, J19.0, 2.4 Hz, 1H), 1.87
(dd, J2.2, 1.5 Hz, 3H); 13C NMR (75 MHz, CDCl3) d
209.9, 160.5, 142.5, 142.0, 129.1, 127.3, 127.2, 44.4, 44.4,
10.3.
Cyclopentenyl cyclopentyl ketone 8b. Rf 0.43 (hexanes/
1
EtOAc 7:1); H NMR (500 MHz, CDCl3) d 6.72±6.71 (m,
1H), 3.36 (dddd, J8.0, 8.0, 8.0, 8.0 Hz, 1H), 2.57±2.52 (m,
4H), 1.94±1.88 (m, 2H), 1.81±1.76 (m, 4H), 1.70±1.64 (m,
2H) 1.61±1.54 (m, 2H); 13C NMR (125 MHz, CDCl3) d
202.0, 145.8, 143.1, 47.3, 34.1, 31.1, 30.4, 26.5, 23.0.
General procedure for the reductive Nazarov cyclization
In a ¯ame-dried 50 mL round-bottom ¯ask equipped with a
magnetic stir bar and rubber septum was prepared a solution
of dienone 1 (1 equiv.) and triethylsilane (2 equiv.) in
CH2Cl2 (0.01 M in 1). To this solution was added
BF3´OEt2 (1.1 equiv.) via syringe at 2788C. The resulting
solution was slowly warmed and the disappearance of
starting material was monitored by TLC. Upon complete
consumption of starting material (08C for 1a,c and 108C
for 1b,d,e) the reaction was quenched by the addition of
1N HCl (or H2O) (10 mL). The resulting mixture was
allowed to stir at 258C overnight. The phases were separated
and the aqueous layer was extracted with CH2Cl2 (20 mL).
The combined organic layers were dried (MgSO4) and
concentrated under reduced pressure. Puri®cation was
achieved using radial chromatography (silica gel, hexanes/
EtOAc 25:1!20:1!15:1)
1-(Triethylsilyloxy)-2,5-dimethyl-3,4-diisopropyl-cyclo-
pent-1-en 6c. Major diastereomer: Rf 0.77 (hexanes/EtOAc
1
7:1); IR (thin ®lm) 1691, 1458 cm21; H NMR (500 MHz,
CDCl3) d 2.19±2.13 (m, 1H), 2.08±2.05 (m, 1H), 1.86±1.77
(m, 1H), 1.56±1.52 (m, 1H), 1.46 (dd, J2.0, 1.1 Hz, 3H),
1.26 (dd, J8.3, 3.8 Hz, 1H), 1.04 (d, J7.0 Hz, 3H), 0.99
(t, J7.9 Hz, 9H), 0.89 (d, J6.8 Hz, 3H), 0.86 (d, J
7.0 Hz, 3H), 0.80 (d, J6.7 Hz, 3H), 0.74 (d, J7.0 Hz,
3H), 0.67 (q, J7.9 Hz, 6H); 13C NMR (125 MHz,
CDCl3) d 149.9, 114.3, 54.1, 48.9, 40.8, 33.1, 29.3, 21.0,
20.5, 20.3, 18.3, 17.7, 11.3, 7.0, 5.7; HRMS for C19H38OSi
calcd 310.2692, found 310.2678.
Mixture of ketones 7c from Entry 7. (Inseparable mixture
of two diastereomers; 2.6:1 ratio by H NMR integration.)
1
Rf 0.41 (hexanes/EtOAc 7:1); IR (thin ®lm) 1739 cm21 13C
;
NMR (125 MHz, CDCl3) d 225.4, 222.0, 46.9, 46.4, 46.1,
44.9, 43.2, 41.9, 33.4, 27.2, 27.1, 22.5, 21.3, 21.1, 19.3,
19.0, 17.4, 15.1, 10.8, 9.4.
1-(Triethylsilyloxy)-2,5-dimethyl-3,4-diphenyl-cyclopent-
1-ene 6a. Rf 10.61 (hexanes/EtOAc 7:1); IR (thin ®lm) 1684,
1601 cm21; H NMR (500 MHz, CDCl3) d 7.29±7.04 (m,
10 H), 3.63 (d, J7.0 Hz, 1H), 2.77±2.71 (m, 1H), 2.61 (dd,
J7.1, 7.1 Hz, 1H), 1.46±1.45 (m, 3H), 1.16 (d, J6.8 Hz,
3H), 1.08 (t, J7.9 Hz, 9H), 0.77 (q, J7.9 Hz, 6H); 13C
NMR (125 MHz, CDCl3) d 151.0, 145.1, 145.1, 128.5,
128.5, 128.2, 127.9, 126.3, 126.3, 113.9, 61.4, 60.2, 48.5,
19.0, 11.3, 7.1, 5.8; Anal. Calcd for C25H34OSi: C, 79.29; H,
9.07. Found: C, 79.35; H, 9.01.
1
Diastereomer A (major). H NMR (500 MHz, CDCl3) d
2.54 (dqd, J9.9, 7.1, 2.6 Hz, 1H), 2.08 (qqd, J7.0, 7.0,
2.5 Hz, 1H), 1.99 (ddd, J9.9, 2.8, 2.8 Hz, 1H), 1.85 (qqd,
J6.8, 6.8, 3.1 Hz, 1H), 1.75 (dqd, J6.7, 6.7, 6.7, 1H),
1.46 (ddd, J6.3, 6.3, 2.6 Hz, 1H), 1.10 (d, J7.2 Hz,
3H), 1.02 (d, J7.0 Hz, 3H), 0.97 (d, J6.7 Hz, 3H), 0.95
(d, J6.7 Hz, 3H), 0.88 (d, J7.0 Hz, 3H), 0.54 (d, J
6.8 Hz, 3H).
2,5-Dimethyl-3,4-diphenyl-cyclopentanone 7ab. Mp
1208C; Rf 0.26 (hexanes/EtOAc 7:1); IR (thin ®lm)
1
Diastereomer B (minor). H NMR (500 MHz, CDCl3) d
1
1744 cm21; H NMR (500 MHz, CDCl3) d 7.25±7.09 (m,
2.34 (dq, J9.7, 7.4 Hz, 1H), 2.11 (dd, J9.8, 2.6 Hz,
1H), 1.95 (qqd, J6.8, 6.8, 2.7 Hz, 1H), 1.09 (d, J7.3 H,
3H), 0.96 (d, J6.8 Hz, 3H), 0.69 (d, J6.8 Hz, 3H).
10H), 2.94 (dd, J12.0, 10.5 Hz, 1H), 2.94 (dd, J12.0,
10.5 Hz, 1H), 2.47 (dq, J12.0, 7.0 Hz, 1H), 2.47 (dq, J
12.0, 7.0 Hz, 1H), 1.14 (d, J7.0 Hz, 6H); 13C NMR
(125 MHz, CDCl3) d 219.8, 140.3, 128.7, 127.8, 127.1,
57.0, 51.8, 13.2; Anal. Calcd for C19H20O: C, 86.31; H,
7.64. Found: C, 86.32; H, 7.70.
Mixture of ketones 7c from Entry 8. (Inseparable mixture
of three diastereomers, including diastereomers A and B
1
from above; 2.8:1.2:1 ratio by H NMR integration.) Rf
0.41 (hexanes/EtOAc 7:1); IR (thin ®lm) 1739 cm21 13C
;
2,5-Dimethyl-3,4-diphenyl-cyclopentanone 7aa. Mp
828C; Rf 0.21 (hexanes/EtOAc 7:1); IR (thin ®lm)
NMR (125 MHz, CDCl3) d 225.4, 223.7, 222.0, 51.0,
46.9, 46.4, 46.1, 44.9, 44.4, 43.2, 41.9, 33.4, 29.4, 27.2,
27.1, 22.5, 22.2, 21.3, 21.1, 19.3, 19.0, 17.8, 17.4, 17.1,
15.1, 10.8, 9.4.
1
1729 cm21; H NMR (500 MHz, CDCl3) d 7.29±7.12 (m,
10 H), 3.89 (dd, J11.9, 8.5 Hz, 1H), 3.28 (dd, J11.9,
11.9 Hz, 1H), 2.85 (dqd, J9.6, 8.1, 1.3 Hz, 1H), 2.45