P. A. Caruana, A. J. Frontier / Tetrahedron 60 (2004) 10921–10926
10925
6.4 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 162.3, 157.8,
128.8, 126.6, 124.3, 121.9, 109.4, 85.7, 65.7, 46.8.
1992, 31, 647. (c) Tomooka, K.; Igarashi, T.; Watanabe, M.;
Nakai, T. Tetrahedron Lett. 1992, 33, 5795.
3. (a) Still, W. C.; Mitra, A. J. Am. Chem. Soc. 1978, 100, 1927.
(b) Balestra, M.; Kallmerten, J. Tetrahedron Lett. 1988, 29,
6901.
4.3.5. 2-Methyl-3-hydroxymethyl benzofuran (3e). Stan-
nane 1e (0.18 g, 0.35 mmol) was dissolved in THF (2.8 mL)
and cooled to K78 8C. MeLi (1.6 M in diethyl ether,
0.47 mL, 0.70 mmol) was then added dropwise and the
reaction was stirred for 30 min. MeOH (0.4 mL), followed
by 0.03 mL TFA was then added and the solution was
allowed to warm to room temperature. The reaction mixture
was then diluted with ether and washed with water (1!).
The aqueous layer was washed with ether (1!), and the
combined ether extracts were washed with saturated sodium
bicarbonate (1!) and brine (1!). The organic phase was
then dried over anhydrous magnesium sulfate and concen-
trated. Silica gel chromatography (dichloromethane/9:1
dichloromethane:ether) afforded 47 mg (80%) of 3e31 as a
white solid.
4. For examples, see (a) McGowan, G. Aust. J. Chem. 2002, 55,
799. (b) Marshall, J. A.; McNulty, L. M.; Zou, D. J. Org.
Chem. 1999, 64, 5193 and references therein. (c) Ref. 1b.
5. For examples of [2,3] rearrangements of furans involving
ylides and stabilized carbanions, see (a) Tsubuki, M.; Kamata,
T.; Okita, H.; Arai, M.; Shigihara, A.; Honda, T. J. Chem. Soc.,
Chem. Commun. 1999, 2263. (b) Usami, T.; Shirai, N.; Sato,
Y. J. Org. Chem. 1992, 57, 5419. (c) Padwa, A.; Gasdaska,
J. R. Tetrahedron 1988, 44, 4147. (d) Cazes, B.; Julia, S. Synth.
Commun. 1977, 7, 113. In all cases, the only products isolated
were furan derivatives.
6. Marko, I. E. In Pattenden, G., Ed.; Comprehensive Organic
Synthesis; Pergamon: London, 1991; Vol. 3, pp 913–974.
7. For a recent report describing the anionic dearomatization of
pyrroles, see Clayden, J.; Turnbull, R.; Pinto, I. Org. Lett.
2004, 6, 609.
4.3.6. Enol ether (2f). Stannane 1f (3.65 g, 7.00 mmol) was
dissolved in THF (46 mL) and cooled to K78 8C. MeLi
(1.6 M in diethyl ether, 13.0 mL, 21.0 mmol) was then
added dropwise and the reaction was stirred for 20 min at K
78 8C. MeOH (6.0 mL) was then added and the solution was
allowed to warm to room temperature. The reaction mixture
was then diluted with ether and washed with water (1!).
The aqueous layer was washed with ether (1!) and the
combined ether extracts were washed with brine (1!). The
organic phase was then dried over anhydrous magnesium
sulfate and concentrated. Silica gel chromatography (4:1
hexane:ethylacetate) afforded 0.984 (80%) of 2f as a faint
yellow oil. IR (thin film) 3390, 2967, 2928, 2868, 1684,
1609, 1476, 1462, 1240, 1172, 1105, 1040, 936, 827,
8. Stannyl methyl ethers were prepared from the reaction of KH
and a 2-furyl alcohol with ICH2SnBu3 (see Supplemental
Information).
9. Yields were low and isolation was difficult, but 1H NMR data
for the dominant product peaks was consistent with expected
enol ethers 2.
10. Catalytic AcOH in THF and 10% aqueous HCl in chlorinated
solvents were equally effective. Rearomatization was
accompanied by decomposition and/or polymerization
pathways.
11. This reaction could be performed on a 7 mmol scale, to give 2f
in 80% yield.
1
750 cmK1; H NMR (400 MHz, CDCl3) d 7.26–7.18 (m,
12. Tulshian, D. B.; Fraser-Reid, B. J. Org. Chem. 1984, 49, 518.
13. The [2,3]-rearrangement of 1c in d8-THF showed no
deuterium incorporation, ruling out proton transfer from the
solvent.
2H), 7.01 (t, JZ7.3 Hz, 1H), 6.94 (d, JZ8.0 Hz, 1H), 4.79
(d, JZ2.7 Hz, 1H), 4.27 (d, JZ2.7 Hz, 1H), 3.69–3.59 (m,
2H), 1.67 (t, JZ7.0 Hz, 1H), 1.45 (s, 3H); 13C NMR
(75 MHz, CDCl3) d 167.8, 156.8, 131.3, 128.6, 123.0,
122.0, 109.4, 84.0, 70.5, 49.7, 23.3; HRMS (EI) m/z
176.08308 [(MC); Calcd for C11H12O2 176.0832].
14. Broka, C. A.; Lee, W. J.; Shen, T. J. Org. Chem. 1988, 53,
1336 and references therein.
15. (a) Sawyer, J. S.; Macdonald, T. L.; McGarvey, G. J. J. Am.
Chem. Soc. 1984, 106, 3376. (b) Coldham, I.; Hufton, R.
Tetrahedron 1996, 52, 12541.
General notes. Enol ether 2c also isomerized to the
corresponding furan 3c under similar acidic conditions in
moderate yield. All methyl ethers 4 were identified
16. Komine, N.; Tomooka, K.; Nakai, T. Heterocycles 2000, 52,
1071.
1
17. (a) See Refs. 7,8(b) Tomooka, K.; Komine, N.; Sasaki, T.;
Shimizu, H.; Nakai, T. Tetrahedron Lett. 1998, 39, 9715. (c)
Tomooka, K.; Komine, N.; Nakai, T. Tetrahedron Lett. 1997,
38, 8939.
according to H NMR (characteristic signal at 3.2 ppm (s,
3H)).
18. For [2,3]-rearrangements of TMS methyl ethers, see: (a)
Maleczka, R. E. J.; Geng, F. Org. Lett. 1999, 1, 1115. (b)
Maleczka, R. E. J.; Geng, F. Org. Lett. 1999, 1, 1111. (c)
Mulzer, J.; List, B. Tetrahedron Lett. 1996, 37, 2403.
19. Spectroscopic data match literature values; (Bushby, N.;
Moody, C. J.; Riddick, D. A.; Waldron, I. R. J. Chem. Soc.,
Perkin Trans. I 2001, 2183.) Trans geometry was assigned on
the basis of coupling constants and proton correlation (COSY).
A likely mechanism involving a) proton transfer b) ring
opening and c) hydrolysis is outlined below.
Acknowledgements
We thank the University of Rochester for support of this
research. We are grateful to Dr. Alice Bergmann (director of
the Chemistry Instrumentation Center at the University of
Buffalo) for performing HRMS analysis.
References and notes
1. (a) Nakai, T.; Mikami, K. 1994, Org. React. (N.Y.) 46, 105. (b)
Marshall, J. A. In Pattenden, G., Ed.; Comprehensive Organic
Synthesis; Pergamon: London, 1991; Vol. 3, pp 975–1014.
2. (a) Verner, E. J.; Cohen, T. J. Am. Chem. Soc. 1992, 114, 375.
(b) Hoffmann, R.; Bru¨ckner, R. Angew. Chem., Int. Ed. Engl.