6942 J . Org. Chem., Vol. 66, No. 21, 2001
Chen et al.
removed in vacuo. Flash chromatography (hexanes/EtOAc,
10:1) gave pure 2m (Rf ) 0.5, 24.7 mg, 24%) as a colorless oil:
1H NMR (400 MHz, CDCl3) δ 0.90 (br dd, J ) 5.2, 5.2 Hz, H2),
1.10 (br dd, J ) 5.2, 5.2 Hz, H4), 1.16 (br dd, J ) 5.2, 5.2 Hz,
H3), 1.31 (dd, J ) 1.4, 1.4 Hz, 2H: H5/5′), 1.76 (br s, H6), 1.77-
1.79 (m, H1), 1.85-1.87 (m, H7), 2.07 (d, 3H: CH3), 2.27 (dddd,
J ) 17.9(AB), 7.1, 3.1, 3.1 Hz, H11), 2.34 (m, H11′), 5.33 (ddd,
J ) 11.9, 4.6, 2.7 Hz, H9), 5.50-5.56 (m, 2H: H8/10); 13C NMR
(75 MHz, CDCl3) 10.5 (C4), 11.5 (C3), 13.9 (C2), 21.5 (CH3),
29.9 (C11), 36.3 (C5), 36.7 (C6), 41.1 (C1), 46.2 (C7), 74.0 (C8),
126.7 (C10), 129.4 (C9), 170.5 (C)O); IR (NaCl) 1757, 1736
cm-1; HRMS (CI, NH3, 140 eV) m/z 222.1482 ([M + NH4]+,
6.8), calcd for C13H20O2 222.1494. The stereochemistry at C8
was assigned by a NOESY experiment: H8 T H6.
Gen er a l P r oced u r e for th e [4 + 2 + 2] Hom o-Diels-
Ald er Rea ction s of Bicyclo[2.2.2]octa -2,5-d ien es 12 a n d
13a -c (Ta ble 4). To a solution of Co(acac)2 and DPPE (1.5
equiv relative to Co) in anhydrous toluene (see individual
compounds for optimized amounts) in a pressure tube cooled
to -30 °C under argon was added Et2AlCl (10 equiv relative
to Co, 1.8 M in toluene) dropwise with stirring, forming a
brown solution. To this active catalyst solution at -30 °C was
added the homodiene and 1,3-butadiene (see individual com-
pounds for optimized amounts) either neat or as a solution in
toluene as indicated below. The reaction vessel was capped
and warmed to the desired temperature for the designated
period of time with continuous stirring. After the mixture was
cooled to room temperature, excess Et2AlCl was quenched by
the dropwise addition of MeOH until the reation mixture
turned green (usually < 1 mL), then the solution was filtered
by suction through a silica gel plug (2 cm) on a glass frit to
remove the catalyst. The silica gel was washed with CH2Cl2
(3 × 5 mL) and the combined CH2Cl2 solutions (now colorless)
were evaporated to dryness in vacuo to provide the crude
product mixture. Flash chromatography gave the target cyclo-
adducts as indicated below.
126.3, 126.8 (2C), 135.0, 143.4; HRMS (EI, 70 eV) m/z 208.1250
([M]+, 28), calcd for C16H16 208.1252.
5,6-o-Tetr ach lor oben zen otetr acyclo[5.5.0.02,4.03,8]dodec-
10-en e (15b). Prepared according to the general procedure
using 13b (100 mg, 0.34 mmol), 1,3-butadiene (1 mL, 11.65
mmol), Co(acac)2 (17.5 mg, 0.068 mmol), and dppe (40.6 mg,
0.102 mmol) in toluene (2 mL). The reaction was maintained
at 55 °C for 6 h and the product purified by flash chromatog-
raphy (hexanes, Rf ) 0.6) to give 15b as a colorless oil (112.6
mg, 95%): 1H NMR (400 MHz, CDCl3) δ 1.46 (dd, J ) 3.8, 3.8
Hz, 2H), 1.55 (dd, J ) 7.3, 1.0 Hz, 2H), 2.39 (br dd, J ) 16.6,
3.0 Hz, 2H), 2.50 (dddd, J ) 16.6, 3.8, 3.8, 1.8 Hz, 2H), 2.70 (t,
J ) 7.3 Hz, 1H), 3.25 (br s, 1H), 5.54 (m, 2H); 13C NMR (75
MHz, CDCl3) δ 18.5, 21.4 (2C), 33.2 (2C), 37.5 (2C), 46.3, 126.3,
126.5 (2C), 128.0, 129.5, 130.4, 134.4, 140.6; HRMS (CI, NH3,
140 eV) m/z 344.9780 ([M + H]+), 0.12), calcd for C16H1335Cl4,
344.9772.
5,6-o-Tetr a ch lor oben zen o-7-m eth oxytetr a cyclo[5.5.0.-
02,4,03,8]d od ec-10-en e (15c). Prepared according to the gen-
eral procedure using 15c (20 mg, 0.06 mmol), 1,3-butadiene
(0.03 mL, 0.37 mmol), Co(acac)2 (3.2 mg, 0.0124, mmol), and
dppe (7.4 mg, 0.0186 mmol) in toluene (0.31 mL). The reaction
was maintained at 100 °C for 53 h and the product purified
by flash chromatography (3% CH2Cl2 in hexanes, Rf ) 0.7) to
give 15c as a colorless oil (16.3 mg, 70%): 1H NMR (400 MHz,
CDCl3) δ 1.62 (d, J ) 7.6 Hz, 2H), 1.78 (dd, J ) 3.4, 2.4 Hz,
2H), 2.30 (dddd, J ) 16.1, 3.9, 3.4, 2.0 Hz, 2H), 2.70 (br dd,
J ) 16.1, 2.4 Hz, 2H), 2.80 (t, J ) 7.6 Hz, 1H), 3.53 (br s, 3H),
5.53 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 19.6, 22.2 (2C), 29.5
(2C), 40.7 (2C), 55.9, 88.3, 125.3, 126.2 (2C), 130.0, 130.3, 130.6,
137.0, 139.6; HRMS (CI, NH3, 140 eV) m/z 373.9824 ([M]+, 26),
calcd for C17H14O35Cl4 373.9800.
5,6-o-Tetr a ch lor oben zen o-7-m eth oxy-10-m eth yltetr a -
cyclo[5.5.0.02,4.03,8]d od ec-10-en e (15d ). Prepared according
to the general procedure using 13d (36.4 mg, 0.11 mmol), 1,3-
butadiene (0.06 mL, 0.56 mmol), Co(acac)2 (7.3 mg, 0.028
mmol), and dppe (16.9 mg, 0.042 mmol) in toluene (0.38 mL).
The reaction was maintained at 110 °C for 48 h, and the
product purified by flash chromatography (1% CH2Cl2 in
hexanes, Rf ) 0.8) to give 15d as a colorless oil (21.2 mg, 48%)
along with recovered 13d (7.3 mg, 20%): 1H NMR (400 MHz,
CDCl3) δ 1.62 (d, J ) 7.8 Hz, 2H), 1.71 (dd, J ) 3.9, 3.4 Hz,
1H), 1.73 (dd, J ) 3.9, 3.4 Hz, 1H), 1.77 (br s, 3H), 2.11 (dd,
J ) 17.4, 3.9 Hz, 1H), 2.21 (ddd, J ) 17.8, 6.6, 3.9 Hz, 1H),
2.66 (br d, J ) 17.4 Hz, 1H), 2.73 (br d, J ) 17.8, 1H), 2.79 (t,
J ) 7.8 Hz, 1H), 3.52 (s, 3H), 5.32 (br d, J ) 6.6 Hz, 1H); 13C
NMR (75 MHz, CDCl3) δ 19.6, 22.1, 22.3, 27.8, 28.8, 34.0, 40.1,
40.5, 55.8, 87.9, 120.7, 125.4, 130.0, 130.3, 130.6, 133.2, 137.1,
139.4; HRMS (CI, NH3, 140 eV) m/z 387.9940 ([M]+, 1.5), calcd
for C18H16O35Cl4 387.9955.
Tet r a cyclo[5.5.0.02,4.03,8]d od ec-10-en e (14). Prepared
according to the general procedure using 12 (212 mg, 2 mmol),
1,3-butadiene (1 mL, 11.65 mmol), Co(acac)2 (103 mg, 0.40,
mmol), and dppe (240 mg, 0.60 mmol) in toluene (2 mL). The
reaction was maintained at 50 °C for 6 h and the product
purified by flash chromatography (hexanes, Rf ) 0.8) to give
14 as a colorless oil (278.4 mg, 87%): 1H NMR (400 MHz,
CDCl3) δ 0.79 (tt, J ) 7.4, 2.4 Hz, 1H), 1.02 (br d, J ) 7.4 Hz,
2H), 1.49 (m, 2H), 1.56 (br s, 1H), 1.77 (m, 2H), 2.01 (br dd,
J ) 3.4, 3.4 Hz, 2H), 2.15 (br dd, J ) 16.4 Hz, 3.2 Hz, 2H),
2.30 (dddd, J ) 16.4, 3.4, 3.4, 1.2 Hz, 2H), 5.42-5.44 (m, 2H);
13C NMR (75 MHz, CDCl3) δ 14.6, 16.5, 22.0 (2C), 30.0, 35.6
(2C), 40.4 (2C), 43.9, 126.9 (2C); HRMS (CI, NH3, 140 eV) m/z
160.1251 ([M]+, 0.9) calcd for C12 H16 160.1252.
5,6-o-Ben zen otetr acyclo[5.5.0.02,4.03,8]dodec-10-en e (15a).
Prepared according to the general procedure using 13a (548
mg, 3.6 mmol), 1,3-butadiene (2 mL, 21.9 mmol), Co(acac)2 (46
mg, 0.18, mmol), and dppe (107 mg, 0.27 mmol) in toluene (12
mL). The reaction was maintained at 60 °C for 24 h and the
product purified by flash chromatography (hexanes, Rf ) 0.4)
to give 15a as a colorless oil (596.1 mg, 80%): 1H NMR (400
MHz, CDCl3) δ 1.38 (dd, J ) 7.4, 1.0 Hz, 2H), 1.49 (dd, J )
3.8, 2.9 Hz, 2H), 2.14 (t, J ) 7.4 Hz, 1H), 2.34 (bdd, J ) 16.1,
2.9 Hz, 2H), 2.46 (dddd, J ) 16.1, 3.8, 3.8, 1.8 Hz, 2H), 2.60
(br s, 1H), 5.52 (m, 2H), 6.96 (dd, J ) 7.3, 1.0 Hz, 1H), 7.04
(ddd, J ) 7.3, 7.3, 1.0 Hz, 1H), 7.11 (ddd, J ) 7.3, 7.3, 1.5 Hz,
1H), 7.22 (br d, J ) 7.3 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ
20.1, 20.7 (2C), 33.7 (2C), 38.5 (2C), 49.9, 122.3, 124.0, 125.7,
Ack n ow led gm en t. We are grateful for financial
support from Research Corporation, the Boston Uni-
versity Community Technology Fund, and the National
Science Foundation, Grant No. CHE-0092061.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and characterization data for 1k ,l, 6a ,b, and 7a ,b and
copies of 1H and 13C NMR spectra of previously unreported
compounds 2c,i,k /l,m , 6a , 7a /b, 14, and 15a -d . This material
J O010268O