1770
B. C. Maiti et al. / Tetrahedron 61 (2005) 1765–1771
3.2. Reactions of the phenylboronates with acetic
anhydride/sodium acetate
3.2.4. 1-Hydroxy-7-methyl-4,5-naphthylene phenyl-
boronate 35. A similar reaction between the phenyl-
boronate 35 (2 g, 7.25 mmol), acetic anhydride (15 ml,
16.2 g, 159 mmol) and anhydrous sodium acetate (300 mg,
3.66 mmol) gave a mixture (essentially 1:2 by NMR) of
5,8-diacetoxy-3-methyl-1-naphthol 37 and 4,8-diacetoxy-6-
methyl-1-naphthol 39 (1.4 g, 5.11 mmol, 71%) as needles,
mp 144–146 8C, from benzene (found: MC, 274.0840.
Calcd for C15H14O5: M, 274.0841); nmax/cmK1 3355
(HOAr), 1757 and 1730 (aryl acetate C]O).
3.2.1. 1,2-Phenylene phenylboronate 28. A mixture of the
phenylboronate13 28 (200 mg, 1.02 mmol), acetic anhydride
(3 ml, 3.24 g, 31.7 mmol) and anhydrous sodium acetate
(50 mg, 0.61 mmol) was kept at 20 8C for 2 h and then
poured into warm water. Extraction with chloroform, which
was then shaken with aqueous sodium hydrogen carbonate
to remove acidic products, gave 2-acetoxyphenol 29
(80 mg, 0.53 mmol, 52%) which crystallised from benzene
in needles, mp 57–58 8C (lit.,14 57–58 8C) (found: MC,
152.0475. Calcd for C8H8O3: M, 152.0473); m/z 152 (28%,
M), 110 (100, MKCH2CO), 92 (36, 110-H2O) and 81 (27,
110-CHO); nmax/cmK1 3380 (phenolic OH) and 1740 (aryl
acetate C]O); dH 2.30 (3H, s, CH3CO2Ar), 5.80 (1H, br.s,
HOAr) and 6.70–7.20 (4H, m, ArH). When a similar
reaction mixture was kept for 20 h two products resulted and
were separated by TLC using chloroform. The first
crystallised from light petroleum–chloroform to give 1,2-
phenylene diacetate (22 mg, 0.11 mmol, 11%) as needles,
mp 64 8C (lit.,14 64 8C) (found: MC, 194.0581. Calcd
for C10H10O4: M, 194.0579); m/z 194 (1%, M), 152 (6,
MKCH2CO) and 110 (100, 152-CH2CO); nmax/cmK1 1760
(aryl acetate C]O); dH 2.25 (6H, s, CH3CO2Ar) and 7.20
(4H, br.s, ArH). The second product was 2-acetoxyphenol
(60 mg, 0.39 mmol, 39%).
Acidification of the sodium hydrogen carbonate washings
gave 1-acetoxy-7-methyl-4,5-naphthylene phenylboronate
36 (50 mg, 0.16 mmol, 2%) which crystallised from
benzene as needles, mp 173–174 8C (found: MC,
318.1065. C19H1511BO4 requires M, 318.1063); m/z 318
(6%, M), 276 (100, MKCH2CO) and 247 (2, 276-CHO);
nmax/cmK1 1765 (aryl acetate C]O) and 1320 (B–O); lmax
/
nm 301infl (log 3 3.75), 310.5 (3.83), 325 (3.85) and 340
(3.86); dH 2.41 (3H, s, CH3CO2Ar), 2.46 (3H, s, CH3Ar),
6.85 (1H, d, JZ8 Hz, H-3), 6.88 (1H, br.s, H-6), 7.07 (1H,
d, JZ8 Hz, H-2), 7.10 (1H, br.s, H-8), 7.42–7.60 (3H, m, m-
and p-H’s of Ph) and 8.04–8.20 (2H, m, o-H’s of Ph).
3.2.5. Methylation of the mixture of diacetoxynaphthols
37 and 39. A solution of diazomethane [from N-methyl-
nitrosourea (12 g, 116 mmol)] in ether (120 ml) was added
to a solution of the diacetoxynaphthols (2.1 g, 7.66 mmol)
in ether (150 ml) and the mixture was kept for 4 d at 20 8C
and then evaporated. Fractional crystallisation of the residue
from light petroleum–chloroform gave, as the major
component, 4-methoxy-7-methyl-1,5-naphthylene diacetate
40 (1.2 g, 4.17 mmol, 54%) as needles, mp 164 8C (found:
MC, 288. 0994. C16H16O5 requires M, 288.0997); m/z 288
(7%, M), 246 (16, MKCH2CO), 204 (100, 246-CH2CO)
and 189 (27, 204-Me); nmax/cmK1 1768 (aryl acetate
C]O); lmax/nm 237infl (log 3 3,74), 296 (3.69), 315
(3.86) and 330 (3.58); dH 2.35 and 2.42 (each 3H, s,
CH3CO2Ar), 2.48 (3H, s, CH3Ar), 3.90 (3H, s, CH3OAr),
6.72 (1H, d, JZ8 Hz, H-3), 6.95 (1H, d, JZ1.5 Hz, H-6),
7.12 (1H, d, JZ8 Hz, H-2) and 7.45 (1H, d, JZ1.5 Hz,
H-8).
3.2.2. Toluene-a,2-diyl phenylboronate 30. A similar
reaction between the phenylboronate15 30 (400 mg,
1.90 mmol), acetic anhydride (6 ml, 6.48 g, 63.5 mmol)
and anhydrous sodium acetate (80 mg, 0.97 mmol) at 20 8C
for 72 h gave a mixture which was separated by TLC into:
(i) 2-(acetoxymethyl)phenyl acetate 32 (145 mg,
0.70 mmol, 37%), an oil (found: MC, 208.0732.
C11H12O4 requires M, 208.0735); m/z 208 (2%, M),
166 (28, MKCH2CO), 106 (100, 166-AcOH) and 78
(50, 106-CO); nmax/cmK1 (film) 1775 (aryl acetate
C]O) and 1745 (alkyl acetate C]O); dH 2.04 (3H, s,
CH3CO2R), 2.29 (3H, s, CH3CO2Ar), 5.08 (2H, s.
ArCH2OAc) and 7.04–7.50 (4H, m, ArH);
(ii) 2-(acetoxymethyl)phenol 31 (94 mg, 0.57 mmol,
30%), also an oil (found: MC, 166.0627. C9H10O3
requires M, 166.0629); m/z 166 (28%, M), 106 (100,
MKAcOH) and 78 (79%, 106-CO); nmax/cmK1 (film)
3385 (phenolic OH) and 1710 (alkyl acetate C]O); dH
2.11 (3H, s, CH3 CO2R), 5.12 (2H, s, ArCH2OAc),
6.88–7.40 (4H, m, ArH) and 7.69 (1H, s, HOAr);
(iii) unreacted phenylboronate (63 mg).
The minor component, 5-methoxy-7-methyl-1,4-naphthyl-
ene diacetate 38 crystallised as prisms (0.55 g, 1.93 mmol,
25%), mp 116–117 8C (found: MC, 288.0994. C16H16O5
requires M, 288.0997); m/z 288 (40%, M), 246 (8, MK
CH2CO), 204 (100, 246-CH2CO) and 189 (16, 204-Me);
nmax/cmK1 1776 (aryl acetate C]O); lmax/nm 287infl (log 3
3.78), 300 (3.85), 315 (3.68) and 330 (3.53); dH 2.35 and
2.43 (each 3H, s, CH3CO2Ar), 2.47 (3H, s, CH3Ar), 3.91
(3H, s, CH3OAr), 6.70 (1H, br.s, H-6), 6.96 (1H, d, JZ8 Hz,
H-3), 7.18 (1H, d, JZ8 Hz, H-2) and 7.23 (1H, br.s, H-8).
This was identical with a specimen of the leucoacetate
prepared from 5-methoxy-7-methyl-1,4-naphthaquinone
(see below).
3.2.3. 1,8-Naphthylene phenylboronate 33. A similar
reaction between the phenylboronate13 33 (50 mg,
0.20 mmol), acetic anhydride (1.5 ml, 1.62 g, 15.9 mmol)
and anhydrous sodium acetate (30 mg, 0.36 mmol) with
stirring for 27 h at 20 8C gave 8-acetoxy-1-naphthol 34
(15 mg, 0.074 mmol, 37%) as needles, mp 129–130 8C,
from benzene (found: MC, 202.0626. C12H10O3 requires M,
202.0629); m/z 202 (5%, M), 160 (100, MKCH2CO), 131
(3, 160-CHO); nmax/cmK1 3400 (HOAr) and 1736 (hydro-
gen-bonded aryl acetate C]O); lmax/nm 298.5 (log 3 3.74),
312.5 (3.67) and 327 (3.62); dH 2.42 (3H, s, CH3CO2Ar) and
6.80–7.80 (7H, m, HOAr and ArH).
The mother-liquor from the above fractional crystallisation,
on being subjected to TLC using chloroform, gave more of
the above methoxy diacetates and two other products. The
faster-moving of these crystallised from light petroleum to
yield 1,4,5-triacetoxy-7-methylnaphthalene 41 (57 mg,
0.18 mmol, 2.5%) as needles, mp 175–176 8C (lit.,16