V. Singh et al. / Tetrahedron 58 (2002) 9729–9736
9733
1H, aromatic H), 6.70 (br s, 1H, aromatic H), 6.4–5.91
(complex m, 1H, CHvCH2), 5.33 (m of d, J¼14.0 Hz, 1H,
CvCH2), 5.20 (m of d, J¼9.0 Hz, 1H, CvCH2), 4.80 (s,
2H, OCH2), 4.55 (s, 2H, OCH2), 4.06 (ddd, J1¼2.5 Hz,
J2¼2.0 Hz, J3¼1.3 Hz, 2H, OCH2), 2.26 (s, 3H, CH3), 1.52
(s, 6H, C(CH3)2). Mass (m/z): 248 (Mþ). ESI HRMS Calcd
for C15H20O3 [MþþNa]: 271.1035. Found 271.1035.
Continued elution with petroleum ether–ethyl acetate
(88:12) gave the dimer 14 as a crystalline colourless solid
(0.21 g, 22%), mp 88–898C. IR (KBr) nmax: 1728,
1
1689 cm21. H NMR (300 MHz, CDCl3): d 6.76 (s, 1H, b
proton of a, b-enone), 5.84–5.98 (complex m, 2H, olefin
proton), 5.77 (m, 1H, olefin proton of b,g-enone), 5.32 (m,
1H), 5.27 (m, 1H), 5.22 (m, 1H), 5.19 (m, 1H), 4.14 (d,
J¼1.6 Hz, 2H), 4.07–3.99 (m, 4H), 3.89 (AB system,
JAB¼8.4 Hz, 2H), 3.16 (part of an AB system, JAB¼6.0 Hz,
1H, OCH2), 2.96 (part of an AB system, JAB¼6.0 Hz, 1H,
OCH2), 2.85 (AB system, JAB¼6.0 Hz, 2H), 2.6 (br m, 1H),
2.2 (d, J¼1.8 Hz, 1H), 1.88 (d, J¼1.6 Hz, 3H, CH3), 1.4 (s,
3H, CH3). 13C NMR (62.5 MHz, CDCl3): d 203.8, 191.7,
147.5, 143.1, 136.5, 134.3, 134.2, 124.8, 117.3, 117.1, 72.7,
71.8, 66.1, 65.6, 62.3, 58.4, 58.1, 58.0, 53.0, 48.2, 46.2,
45.6, 23.9, 20.8 (24 carbons). Mass (m/z): 206 (Mþ/2) (it
undergoes retro Diels–Alder reaction during mass spec-
trometry). ESI HRMS: Calcd for C24H28O6 [MþþNa]:
435.1778. Found 435.1785.
4.1.2. 2-Hydroxymethyl-4-methyl-6-(2-oxa-pent-4-ene)-
phenol (11). To a solution of 10b (1 g, 4.03 mmol) in
tetrahydrofuran (40 mL) was added hydrochloric acid (1N,
40 mL) and the reaction mixture was stirred for 12 h at
ambient temperature (,308C). The organic solvent was
removed under reduced pressure at ,408C. The aqueous
solution was extracted with ethyl acetate (3£30 mL). The
combined organic layer was washed with sodium bicarbon-
ate solution (2£10 mL), brine (2£15 mL) and dried over
anhydrous sodium sulphate. Solvent was removed at ,35–
408C under reduced pressure and the crude product was
chromatographed on silica gel. Elution with petroleum
ether–ethyl acetate (9:1) gave the title compound 11 as a
colourless liquid (0.73 g, 88%). IR (neat) nmax: 3356,
4.1.4. 3-Oxa-8,11-dimethyl-endo-tricyclo [5.2.2.01,5]-
undec-10-ene-9-one (15). To a solution of the adduct 13
(1 g, 4.86 mmol) in 30 mL dry dioxane, was added activated
zinc (5 g, excess) and ammonium chloride (1 g, 18.7 mmol,
excess) and the reaction mixture was refluxed for 8 h. After
completion of reaction, the reaction mixture was filtered
through a celite pad, which was then washed with ethyl
acetate. The filtrate was concentrated in vacuo. The residue
was diluted with water (20 mL) and extracted with ethyl
acetate (3£30 mL). The combined organic extract was
washed with brine (2£20 mL) and dried over anhydrous
sodium sulphate. Removal of solvent under reduced
pressure gave the crude product, which was chromato-
graphed (petroleum ether–ethyl acetate, 95:5) to give the
compound 15 (mixture of syn/anti isomers) as a solid
(0.56 g, 60%) mp 56–588C. IR (KBr) nmax: 1712
1
1483 cm21. H NMR (300 MHz, CDCl3): d 7.78 (s, 1H,
OH), 6.95 (s, 1H, aromatic H), 6.8 (s, 1H, aromatic H), 6.2–
5.88 (complex m, 1H, CHvCH2), 5.32 (m of d, J¼14.0 Hz,
1H, CvCH2), 5.25 (m of d, J¼9.0 Hz, 1H, CvCH2), 4.7 (br
s, 2H, OCH2), 4.67 (s, 2H, OCH2), 4.08 (m of d, J¼6.0 Hz,
2H, OCH2), 2.54 (br s, 1H, OH), 2.24 (s, 3H, CH3). Mass
(m/z): 208 (Mþ). ESI HRMS: Calcd for C12H16O3
[MþþNa]: 231.0992. Found 231.0999.
4.1.3. 3-Oxa-11-methyl-8-spiroepoxy-endo-tricyclo-
[5.2.2.01,5]undec-10-en-9-one (13). To a solution of 11
(1 g, 4.8 mmol) in acetonitrile (50 mL) was added a solution
of sodium metaperiodate (5 g, 23.3 mmol, in water (50 mL))
in about 1 h, at ,108C. The reaction mixture was stirred for
12 h. It was then saturated with sodium chloride and
acetonitrile layer was separated. It was washed with brine
(2£10 mL) and dried over anhydrous sodium sulfate. The
remaining aqueous layer was extracted with ethyl acetate
(3£30 mL) and washed with brine (3£10 mL). It was dried
over anhydrous sodium sulfate. Both the acetonitrile and
ethyl acetate extracts were combined and the solvent was
removed under reduced pressure. The residue was chro-
matographed on silica gel. Elution with petroleum ether–
ethyl acetate (95:5) gave the adduct 13 (0.57 g, 58%) as a
solid which was recrystallized from petroleum ether–ethyl
acetate (97:3). mp 1028C. IR (KBr) nmax: 1727 cm21. UV
(MeOH), lmax: 220 and 305 nm. 1H NMR (300 MHz,
CDCl3): d 5.60 (br m, 1H, olefin H), 4.25 (part of an AB
system, JAB¼8.8 Hz, 1H, OCH2), 4.07 (superimposed dd,
J1¼J2¼7.5 Hz, 1H), 3.94 (part of an AB system,
JAB¼8.8 Hz, 1H), 3.30 (dd, J1¼11.0 Hz, J2¼7.5 Hz, 1H,
OCH2) for oxy-methylene protons and 3.19 (part of an AB
system, JAB¼6.0 Hz, 1H, oxirane CH2), and 2.91 (part of
an AB system, JAB¼6.0 Hz, 1H, oxirane CH2), 2.74–2.62
(complex m, 1H), 2.41 (m, 1H), 2.32–2.22 (complex
m, 1H), 1.96 (d, J¼1.6 Hz, 3H, CH3), 1.30 (ddd,
J1¼12.5 Hz, J2¼6.6 Hz, J3¼1.5 Hz, 1H). 13C NMR
(75 MHz, CDCl3): d 201.3 (CO), 146.0, 122.7, 71.2, 68.5,
60.5, 56.9, 51.6, 45.2, 43.7, 23.7, 20.0. Mass (m/z): 206
(Mþ). Analysis: Found C, 70.16; H, 6.86% requires C, 69.9,
H, 6.7% for C12H14O3.
1
(CO) cm21. UV (MeOH) nmax: 219 and 291 nm. H NMR
(300 MHz, CDCl3): d 5.48 (m, 1H, b H of b,g-enone
group), 4.19 (two sets of part of an AB system, JAB¼9.0 Hz,
total 1H, OCH2), 3.99 (two sets of superimposed dd,
J¼7.5 Hz, total 1H), 3.88 (part of an AB system,
JAB¼9.0 Hz, 1H, OCH2), 3.20 (dd, J1¼11.0 Hz,
J2¼7.5 Hz, 1H), 2.64–2.57 (m, 1H), 2.45–2.30 (m, 1H),
2.12–1.96 (m, 2H), 1.91 and 1.90 (two sets of d, J¼1.5 Hz,
total 3H, CH3), 1.24–1.15 (m partly hidden under methyl
signal, 1H), 1.14 and 0.99 (two sets of d, J¼6.0 Hz, total 3H,
CH3). Analysis: Found: C, 74.79%, H, 8.6%; Calcd: C,
75%, H, 8.3% for C12H16O2.
4.1.5. 3-Oxa-11-methyl-8-hydroxymethyl-endo-tricyclo-
[5.2.2.01,5]undec-10-ene-9-one (17). To a suspension of
activated zinc (7 g, excess) in MeOH–H2O (7:1, 25 mL)
was added a solution of adduct 13 (1 g, 3.85 mmol),
followed by addition of ammonium chloride (1 g,
18.7 mmol, excess) and the reaction mixture was stirred at
room temperature (,308C) for about 12 h. The reaction
mixture was filtered through a celite pad, which was further
washed with ethyl acetate (6£10 mL). The filtrate was
concentrated in vacuo. The residue was diluted with water
(20 mL) and extracted with ethyl acetate (3£30 mL). The
combined organic extract was washed with water
(2£10 mL), brine (2£10 mL) and dried over anhydrous
sodium sulphate. Removal of solvent under reduced