3554
M. J. Piggott, D. Wege / Tetrahedron 62 (2006) 3550–3556
Further elution gave methyl 3-[(methoxycarbonyloxy)-
methyl]naphthalene-2-carboxylate (20) as a white crystal-
line solid (0.10 g, 25%), which crystallised from petrol as
colourless needles, mp 66–68 8C; (Found: C, 65.90, H, 5.08.
C15H14O5 requires C, 65.69, H, 5.15%); MS m/z 274 (M,
12%), 183 (100), 127 (16), 57 (23); 1H NMR (300 MHz) d
8.59 (s, 1H, H1), 7.95 (br s, 1H, H4), 7.93–7.85 (m, AB part
of ABXY, 2H, Ar), 7.63–7.51 (m, XY part of ABXY, 2H,
Ar), 5.73 (d, J4,CH2Z0.8 Hz, 2H, CH2), 3.96 (s, 3H, CH3O),
3.84 (s, 3H, CH3O); 13C NMR (75.5 MHz) d 167.1 (CO2),
155.6 (OCO2), 134.7 (Ar), 132.8 (ArH), 132.6 (Ar), 131.9
(Ar), 128.8 (ArH), 128.6 (ArH), 127.8 (ArH), 127.7 (ArH),
127.0 (ArH), 125.9 (Ar), 68.2 (CH2O), 54.9 (CH3O), 52.2
(CH3O).
tetrachloride (26 mL, 0.24 mol) in anhydrous DCM (45 mL)
was added to a stirred solution of 1,4-dimethoxybenzene
(13.82 g, 0.10 mol) in anhydrous DCM (200 mL) at 0 8C
under argon, whereupon the colourless solution turned deep
red. The reaction mixture was treated dropwise with a
solution of dichloromethoxymethane (12.36, 0.14 mol) in
anhydrous DCM (90 mL) over 1.5 h. The ice bath was
removed and stirring was continued for 30 min before the
reaction mixture was poured onto a mixture of ice (300 g)
and concentrated HCl (8 mL). The biphasic mixture was
stirred for 2 h, during which time the dark red organic layer
turned green. The phases were separated and the aqueous
layer was extracted with ether (2!200 mL). The combined
organic solutions were washed with water (3!200 mL) and
brine (200 mL), dried and evaporated to give essentially
pure 32 as a green oil, which solidified on standing (16.57 g,
100%), and crystallised from ether as pale green micro-
needles, mp 48–50 8C (lit.41 53 8C); 1H NMR (200 MHz) d
10.37 (s, 1H, CHO), 7.25 (d, J6,4Z3.3 Hz, 1H, H6), 7.06 (m,
1H, H4), 6.87 (d, J3,4Z9.0 Hz, 1H, H3), 3.82 (s, 3H, CH3O),
3.73 (s, 3H, CH3O). The spectrum was similar to that
reported.42
On another occasion, a small amount of the double adduct,
methyl 5a,5aa,6a,11aa-5,6-bis[(t-butyldimethylsilyl)oxy]-
11a-[(methoxycarbonyl)methoxy]-5,5a,6,11,11a,12-hexa-
hydronaphthacene-5a-carboxylate (21), was isolated by
1
rapid silica filtration as a colourless oil (27 mg, 3%); H
NMR (300 MHz)§ d 7.01 (ddd, JB,CZJB,AZ7.4 Hz, JB,D
Z
1.4 Hz, 2H, Ar [B]), 6.94 (ddd, JC,BZ7.4 Hz, JC,DZ7.4 Hz,
JC,AZ1.0 Hz, 2H, Ar [C]), 6.85 (dd, JA,BZ7.4 Hz, JA,C
Z
1.0 Hz, 2H, Ar [A]), 6.82 (d, JD,CZ7.4 Hz, 2H, Ar [D]),
4.92 (s, 2H, H5/H6 or CH2O), 4.77 (s, 2H, H5/H6 or CH2O),
4.1.7. Ethyl 4-(2,5-dimethoxyphenyl)-4-hydroxy-2-
butynoate (33). A 1.18 M solution of n-BuLi in hexane
(8.5 mL, 10 mmol) was added dropwise to a stirred solution
of ethyl propiolate (981 mg, 10 mmol) in anhydrous THF
(20 mL) at K78 8C under argon. After 10 min a solution of
32 (1.662 g, 10.0 mmol) in anhydrous THF (20 mL) was
added dropwise. Stirring was continued for 10 min and then
for a further 10 min with the cryogenic bath removed.
Acetic acid (2 mL, 35 mmol) was added and the reaction
mixture was allowed to warm to room temperature before
being partitioned between ether (100 mL) and saturated
aqueous sodium bicarbonate (100 mL). The layers were
separated and the aqueous phase was extracted with ether
(2!50 mL). The combined ether solution was washed with
saturated aqueous sodium bicarbonate (50 mL), water
(50 mL) and brine (50 mL), dried and evaporated to give
a red-brown oil, which was subjected to rapid silica
filtration. Elution with EtOAc/petrol (1:19) gave unreacted
32 (233 mg). Further elution with EtOAc/petrol (1:4) gave
33 as a honey coloured oil (1.870 g, 71%, 82% based on
recovered 32); MS (FAB) m/z 264 (M, 80%), 247 (100), 175
(20), 165 (39); HRMS found: 247.0986. [C14H16O5–H2O]C
3.80 (s, 3H, CH3O), 3.66 (s, 3H, CH3O), 3.33 (d, Jgem
Z
15.4 Hz, 2H, H11a/H12a), 2.59 (d, JgemZ15.4 Hz, 2H,
H11b/H12b), 0.79 (s, 18H, t-Bu), 0.00 (s, 6H, SiCH3),
K0.31 (s, 6H, SiCH3); 13C NMR (75.5 MHz) d 170.9
(CO2), 155.8 (OCO2), 136.6 (Ar), 136.2 (Ar), 127.9 (ArH),
127.8 (ArH), 127.3 (ArH), 125.4 (ArH), 75.6 (CH2O), 74.7
(C5/C6), 62.1 (C5a), 54.6 (CH3O), 51.4 (CH3O), 41.2
(C11a), 38.3 (C11/C12), 25.8, (C[CH3]3), 18.1 (SiC), K4.3
(SiCH3), K4.6 (SiCH3).
4.1.5. Attempted reduction–deprotection of the Diels–
Alder adduct (19). A stirred solution of 19 (100 mg,
0.25 mmol) in anhydrous DCM (15 mL) in an ice/salt bath
under argon, was treated dropwise with a 1.2 M toluene
solution of DIBAL (1.25 mL, 1.5 mmol). After 2 h the
solution was allowed to warm to room temperature and the
excess DIBAL was quenched with methanol (5 mL). Ice-
cold 1 M HCl (50 mL) was added and the phases were
separated. The aqueous layer was extracted with DCM (3!
20 mL) and the combined organic solution was dried and
evaporated to give naphthalene-2,3-dimethanol as a white
solid (38 mg, 82%), which crystallised from DCM/petrol as
1
requires 247.0970; H NMR (300 MHz, C6D6)¶ d 7.07 (d,
0
0
0
0
0
0
0
J6 ,4 Z3.1 Hz, 1H, H6 ), 6.66 (dd, J4 ,3 Z8.9 Hz, J4 ,6
Z
3.1 Hz, 1H, H40), 6.34 (d, J3 ,4 Z8.9 Hz, 1H, H3 ), 5.63 (br
0
1
colourless rhomboids, mp 160 8C (lit.20 160 8C); H NMR
0
0
(500 MHz, d6-DMSO) d 7.47 (s, 2H, H1/H4), 7.43 (m, AA0
part of AA0BB0, 2H, Ar), 7.08 (m, BB0 part of AA0BB0, 2H,
Ar), 4.77 (br t, JZ5.0 Hz, 2H, OH), 4.45 (d, JZ5.0 Hz, 4H,
CH2); 13C NMR (125.8 MHz, d6-DMSO) d 137.0 (Ar),
131.8 (Ar), 126.6 (ArH), 126.2 (ArH), 125.0 (ArH), 62.0
(CH2). The 1H NMR spectrum is somewhat different to that
published at lower field.20
d, J4,OHZ7.1 Hz, 1H, H4), 3.81 (q, JZ7.1 Hz, 2H, CH2O),
3.29 (s, 3H, CH3O), 3.19 (s, 3H, CH3O), 2.92 (br d, JOH,4
Z
7.1 Hz, 1H, OH), 0.78 (t, JZ7.1 Hz, 3H, CH3); 13C NMR
(75.5 MHz, C6D6) d 154.4 (C), 153.5 (C), 150.9 (C), 128.8
(C10), 115.0 (ArH), 113.4 (ArH), 112.5 (ArH), 87.1 (C3),
77.3 (C2), 61.7 (CH2O), 61.0 (C4), 55.6 (CH3O), 55.2
(CH3O), 13.7 (CH3); IR nmax br 3446 (OH), 2233 (C^C),
1709 cmK1 (CO).
4.1.6. 2,5-Dimethoxybenzaldehyde (32). The methodology
of Scarpatie et al. was used.40 A solution of titanium
4.1.8. Ethyl 4-[(2,5-dimethoxyphenyl)(hydroxy)methyl]-
3-furoate (35). A mixture of 33 (1.016 g, 3.8 mmol),
4-phenyloxazole (34)41 (2.72 g, 18.7 mmol) and hydro-
quinone (5 mg) under argon, was stirred at 200 8C for 1.5 h,
§ The designations A,B,C,D are meant only to represent the relationship of
the Ar protons to each other as determined by the coupling constants.
Thus, A and D correspond to H1/H10 and H4/H7; B and C correspond to
H2/H9 and H3/H8, but not necessarily, respectively, as shown.
¶ The 1H NMR. spectrum in CDCl3 was not first order.