2772 J . Org. Chem., Vol. 61, No. 8, 1996
Kraus and Zhao
in a separatory funnel until the layers were clear. The organic
phase was then separated, washed with water and brine, dried
over MgSO4, and concentrated in vacuo. The residue was
purified by sgc (H:EA ) 50:1), to give 8.60 g (89% yield) of 3
and 0.96 g (10% yield) of 4-methoxy-2,6-dimethylbenzaldhyde.
3,4-Dih yd r o-8-m et h oxy-6-m et h yl-2-n a p h t h a len eca r -
boxa ld eh yd e (4). To a solution of aldehyde 3 (4.00 g, 24.4
mmol) in 120 mL of dry benzene was added acrolein (2.74 g,
48.8 mmol). The resulting solution was degassed with argon
at 5 °C for 20 min. It was irradiated in a Rayonet reactor
(with a 3500 Å light source) for 3 days. PTSA (388 mg, 2.04
mmol) was added to the above solution. The solution was
stirred for 48 h at rt, worked up with saturated sodium
bicarbonate solution, and extracted with ether. The ether
layer was washed with brine, dried with Na2SO4, and concen-
trated in vacuo. After sgc (10:1 ) H:EA), 4.18 g (85% yield)
of 4 was obtained as a white solid (mp 96 °C): NMR (CDCl3)
δ 2.35 (s, 3H), 2.51 (t, J ) 7.8 Hz, 2H), 2.78 (t, J ) 7.8 Hz,
2H), 3.87 (s, 3H), 6.58 (s, 1H), 6.63 (s, 1H), 7.69 (s, 1H), 9.63
(s, 1H); IR (CDCl3) cm-1 2942, 2815, 1662, 1614, 1567, 1376,
1201, 1091, 909; MS m/ e 100, 115, 128, 143, 159, 174, 181,
202; HRMS m/ e for C13H14O2 calcd 202.0988, measured
202.0988; 13C NMR (CDCl3) δ 18.7, 21.9, 27.2, 55.3, 109.5,
118.5, 121.0, 136.8, 139.4, 140.5, 142.4, 150.5, 192.6.
3,4-Dih yd r o-8-m et h oxy-1,6-d im et h yl-2-n a p h t h a len e-
ca r boxa ld eh yd e (6). To a solution of benzocyclobutanol 8
(2.00 g, 11.2 mmol) in benzene in a sealable tube was added
acrolein (3.14 g, 56.1 mmol). The resulting solution was
degassed with argon for 15 min at 0 °C and heated to 200 °C
for 20 h. PTSA (213 mg, 1.12 mmol) was added to the solution.
The mixture was stirred for 48 h at rt, worked up with
saturated sodium bicarbonate solution, and extracted with
ether. The ether layer was washed with brine, dried over
MgSO4, and concentrated in vacuo. The residue was purified
by sgc (H:E ) 30:1) to afford 2.16 g (89% yield) of 6 as a white
solid (mp 74-75 °C): NMR (CDCl3) δ 2.32 (s, 3H), 2.34-2.37
(m, 2H), 2.52-2.57 (m, 2H), 2.60 (t, J ) 1.3 Hz, 3H), 3.83 (s,
3H), 6.63 (s, 2H), 10.31 (s, 1H); IR (CDCl3) cm-1 2939, 1650,
1593, 1195, 1111, 1031, 834; MS m/ e 43, 63, 77, 91, 115, 128,
172, 187, 201, 216; HRMS m/ e for C14H16O2 calcd 216.1150,
measured 216.1153; 13C NMR (CDCl3) δ 16.4, 19.6, 21.4, 28.9,
55.1, 110.9, 120.9, 122.3, 134.2, 141.0, 141.5, 150.4, 157.9,
190.1.
9-Ch lor o-5,6-d ih yd r o-7-h yd r oxy-1-m eth oxy-3-m eth yl-
ben z[a ]a n th r a cen e-8,11-d ion e (10). F r om 6. To a solution
of aldehyde 6 (240 mg, 1.11 mmol) and triethylamine (2.49
mL, 17.8 mmol) in 20 mL of THF was added trimethylsilyl
triflate (1.72 mL, 8.88 mmol) dropwise at -78 °C. After 5 min,
the mixture was put in an ice bath and then allowed to warm
to rt over 3 h. The THF was replaced with 50 mL of pentane,
and the mixture was flushed through a short Celite pad. The
pentane solution was concentrated in vacuo to afford a
yellowish unstable oil. The oil was dissolved in 6 mL of THF
and was added to a solution of 2,6-dichlorobenzoquinone (216
mg, 1.22 mmol) in 6 mL of THF at rt. The resulting solution
was boiled for 10 h. The THF was replaced with acetone (12
mL). J ones reagent (0.82 mL, 2.2 mmol) was added to the
acetone solution at 0 °C. After 30 min, the mixture was diluted
with water and extracted with ether. The ether layer was
washed with brine, dried over MgSO4, and concentrated in
vacuo. The residue was purified by sgc (H:E ) 30:1) to give
24 mg of 10 (6% yield) as a dark red solid (mp ∼230 °C with
decomposition).
F r om 11. To a solution of LDA (0.15 mmol) in 1 mL of THF
(prepared from diisopropylamine (0.021 mL, 0.15 mmol) and
n-butyllithium (0.06 mL, 0.15 mmol)) was added a solution of
ester 11 (38 mg, 0.15 mmol) in 1 mL of THF at -78 °C. The
resulting solution was stirred for 40 min. TMSCl (0.024 mL,
0.18 mmol) was added to the solution. After 30 min, the
solution was slowly warmed to rt (1.5 h). The THF was
replaced with pentane. The resulting suspension was quickly
flushed through a short Celite pad. The solution was concen-
trated in vacuo. A labile yellowish oil was obtained. The oil
was dissolved in 1 mL of THF and was added to a solution of
2,6-dichloroquinone (28 mg, 0.15 mmol) in 1 mL of THF at
-78 °C. The resulting solution was slowly warmed to rt and
stirred overnight. Several drops of 6 N HCl were added to
the solution followed by the addition of 1 g of silica gel. The
THF was removed in vacuo, and the residue was allowed to
stand overnight. The residue was then washed with ether.
The ether solution was dried over MgSO4 and concentrated in
vacuo. The residue was purified by sgc (H:EA ) 30:1) to afford
52 mg (95% yield) of 10 as a red solid (mp ∼230 °C with
decomposition): NMR (CDCl3) δ 2.39 (s, 3H), 2.74-2.78 (m,
2H), 2.89-2.92 (m, 2H), 3.94 (s, 3H), 6.74 (s, 2H), 7.17 (s, 1H),
8.61 (s, 1H), 12.13 (s, 1H); IR (CDCl3) cm-1 3415, 1654, 1626,
1596, 1280, 1033; MS m/ e 45, 77, 101, 145, 170, 189, 219, 251,
275, 339, 354; HRMS m/ e for C20H15O4Cl calcd 354.0659,
measured 354.0657; 13C NMR (CDCl3) δ 20.7, 21.8, 28.8, 55.7,
109.1, 111.1, 111.9, 120.9, 121.5, 128.9, 133.4, 136.8, 141.0,
141.4, 142.2, 145.8, 157.9, 159.1, 182.3, 182.5; TLC (H:E ) 30:
1) Rf ) 0.11.
6-Meth oxy-1,4-d im eth ylben zocyclobu ten ol (8). A solu-
tion of 7 (3.00 g, 16.8 mmol) in 150 mL of acetone was degassed
with argon for 20 min and irradiated in a Hanovia apparatus
(450 medium pressure lamp in a quartz immersion vessel) for
5 days. The solvent was removed in vacuo. The residue was
purified by sgc (H:EA ) 5:1), giving 2.70 g (90% yield) of 8
and 0.29 g of 7. The product 8 was a white solid (mp 79 °C):
NMR (CDCl3) δ 1.69 (s, 3H), 2.29 (s, 3H), 2.64 (s, 1H), 3.24 (d,
J ) 14.1 Hz, 1H), 3.10 (d, J ) 14.1 Hz, 1H), 3.88 (s, 3H), 6.49
(s, 1H), 6.56 (s, 1H); IR (CDCl3) cm-1 3593, 3412, 2973, 1607,
1576, 1226, 908, 835; MS m/ e 43, 51, 65, 77, 91, 105, 120,
148, 163, 178; HRMS m/ e for C11H14O2 calcd 178.0994,
measured 178.0995; 13C NMR (CDCl3) δ 20.8, 26.0, 27.7, 47.3,
55.7, 114.9, 117.7, 131.3, 140.8, 142.5, 153.2; TLC (H:EA )
5:1) Rf ) 0.4.
Dim eth yl Eth er of G-2N (13). To a solution of 10 (50 mg,
0.14 mmol) in 1 mL of THF was added a solution of 1,3-
dimethoxy-1-((trimethylsilyl)oxy)butadiene (12) (57 mg, 0.28
mmol) in 1 mL of THF at -30 °C. The resulting solution was
slowly warmed to rt and stirred overnight. Several drops of 6
N HCl were added to the above solution followed by the
addition of 1.0 g of silica gel. The THF was removed, and the
residue was allowed to stand overnight. The solid was washed
with ether, dried over MgSO4
, and concentrated in vacuo. The
residue was purified by sgc (H:E ) 20:1) to give 53 mg (91%
yield) of 13 as an orange solid (mp >300 °C): NMR (CDCl3) δ
2.39 (s, 3H), 2.75-2.80 (m, 2H), 2.90-2.95 (m, 2H), 3.94 (s,
3H), 3.96 (s, 3H), 6.69 (d, J ) 2.3 Hz, 1H), 6.75 (s, 2H), 7.40
(d, J ) 2.3 Hz, 1H), 8.79 (s, 1H), 12.43 (s, 1H), 12.56 (s, 1H);
IR (KBr) cm-1 3358, 1629, 1596, 1333, 1266, 1156, 1037; MS
m/ e 45, 91, 158, 208, 232, 285, 332, 416; HRMS m/ e for
C25H20O6 calcd 416.1260, measured 416.1260; 13C NMR (CDCl3)
δ 20.7, 21.7, 28.8, 55.6, 56.0, 106.5, 107.9, 110.6, 111.0, 113.2,
119.1, 120.9, 121.4, 130.5, 133.5, 135.7, 140.8, 141.0, 141.4,
157.8, 159.0, 165.1, 166.4, 182.3, 190.7; TLC (H:EA ) 5:1) Rf
) 0.32. Anal. Calcd for C25H20O6: C, 72.11; H, 4.84. Found:
C, 72.36; H, 4.47.
Met h yl 3,4-Dih yd r o-8-m et h oxy-1,6-d im et h yl-2-n a p h -
th a len eca r boxyla te (11). To a solution of benzocyclobutenol
8 (1.00 g, 5.61 mmol) in 20 mL of benzene in a sealable tube
was added methyl acrylate (3.86 g, 44.9 mmol). The resulting
solution was degassed with argon for 15 min at 0 °C and
heated to 200 °C for 20 h. PTSA (107 mg, 0.561 mmol) was
added to the above solution. The mixture was stirred for 48
h at rt, worked up with saturated sodium bicarbonate solution,
and extracted with ether. The ether layer was washed with
brine, dried, and concentrated in vacuo. The residue was
purified by sgc (H:EA ) 50:1) to give 1.19 g (86% yield) of 11
as a colorless oil: NMR (CDCl3) δ 2.33 (s, 3H), 2.40-2.45 (m,
2H), 2.47 (br s, 3H), 2.57-2.62 (m, 2H), 3.79 (s, 3H), 3.87 (s,
3H), 6.63 (s, 2H); IR (CDCl3) cm-1 2946, 1707, 1609, 1352,
1278; MS m/ e 51, 70, 91, 115, 128, 156, 172, 187, 199, 215,
231, 246; HRMS m/ e for C15H18O3 calcd 246.1256, measured
246.1255; 13C NMR (CDCl3) δ 20.3, 21.5, 24.5, 29.6, 51.3, 55.3,
111.1, 120.5, 123.3, 126.3, 139.4, 140.5, 143.5, 157.4, 169.2.
Met h yl 3,4-Dih yd r o-8-h yd r oxy-1,6-d im et h yl-2-n a p h -
th a len eca r boxyla te (15). To a solution of ester 11 (0.100 g,
0.41 mmol) in 4 mL of dry CH2Cl2 was added BBr3 (0.16 mL,
1.64 mmol) at -78 °C dropwise. The mixture was stirred for
0.5 h at -78 °C, warmed up to -20 °C slowly, and stirred for