124
D. Hobuß et al.
LETTER
(7) Takada, S.; Adachi, M. (Shionogi Seiyaku Kk), Jpn. Kokai
Tokkyo Koho JP 07,145,162, 1995; Chem. Abstr. 1995, 123,
227991f.
OEt
OEt
BF3·OEt2
EtO
OEt EtOBF3
EtO
(8) Dornow, A.; Ische, F. Angew. Chem. 1955, 67, 653.
(9) Mock, W. L.; Tsou, H.-R. J. Org. Chem. 1981, 46, 2557.
(10) Preparation of 1,1,5,5-Tetraethoxy-3-pentanone (10b) on
a Multi-Gram Scale.
12
13
i-Pr2NEt
+ 2
O
A solution of BF3·OEt2 (46.60 mL, 0.36 mol) in CH2Cl2 (40
mL) was added dropwise over 15 min to 12 (44.46 g, 0.30
mol) at –30 °C. The stirred reaction mixture was warmed up
to 0 °C for 20 min, and then cooled to –78 °C. After addition
of absolute acetone (4.41 mL, 0.06 mol), i-Pr2NEt (55.5 mL,
0.36 mol) was added dropwise over 20 min. The reaction
mixture was stirred at –78 °C for 2.5 h, poured into concd
NaHCO3 solution (500 mL), stirred for 10 min, and was then
extracted with CH2Cl2 (3 × 100 mL). The combined organic
layers were washed successively with ice cold 2 N H2SO4
(75 mL) and H2O (2 × 100 mL), and dried (MgSO4). The
solvent was removed under vacuum and the residue was
distilled through a Vigreux column to give 10b (10.10 g,
64%) as a light yellow liquid, bp 105 °C/0.18 mbar (bp 71–
71.5 °C/0.025 mm).9 1H NMR (250 MHz, C6D6): d = 1.19 (t,
J = 7.0 Hz, 12 H, 7-H), 2.79 (d, J = 5.6 Hz, 4 H, 2-H, 4-H),
3.60 (m, 8 H, 6-H), 4.91 (t, J = 5.6 Hz, 2 H, 1-H, 5-H) ppm.
13C NMR (62 MHz, C6D6): d = 15.2 (C-7), 48.5 (C-6), 62.3
(C-2, C-4), 99.6 (C-1, C-5), 204.8 (C-3) ppm.
OEt
O
OEt
OEt
H2SO4
EtOH
reflux
EtO
O
1 (92%)
10b (64%)
Scheme 3
References
(1) (a) Hepworth, J. D.; Heron, B. M. Prog. Heterocycl. Chem.
2002, 14, 332. (b) Mascarenas, J. L. Adv. Cycloaddit. 1999,
6, 1. (c) West, F. G. Adv. Cycloaddit. 1997, 4, 1.
(d) Staunton, J. Comprehensive Organic Chemistry, Vol. 4;
Sammes, P. G., Ed.; Pergamon: Oxford, 1979, 659–692.
(2) Willstätter, R.; Pummerer, R. Ber. Dtsch. Chem. Ges. 1905,
38, 1461.
(3) (a) Lieben, A.; Haitinger, L. Ber. Dtsch. Chem. Ges. 1883,
16, 1259. (b) Claisen, L. Ber. Dtsch. Chem. Ges. 1891, 24,
111. (c) Toomey, R. F.; Riegel, E. R. J. Org. Chem. 1952,
17, 1492. (d) Horvárth, G.; Rusa, C.; Köntös, Z.; Gerencser,
J.; Huszthy, P. Synth. Commun. 1999, 29, 3719.
(4) Pauson, P. L.; Proctor, G. R.; Rodger, W. J. J. Chem. Soc.
1965, 3037.
(11) Antus, S.; Boross, F.; Kajtár-Peredy, M.; Radics, L.;
Nógrádi, M. Liebigs Ann. Chem. 1980, 1283.
(12) Preparation of g-Pyrone (1) from Tetraethoxypentanone
(10b). In a sealed Schlenk flask a solution of 10b (2.62 g,
10.0 mmol) in EtOH (50 mL) and 10% H2SO4–H2O (5 mL)
was heated at 80 °C for 24 h. The reaction mixture was then
neutralized with NaHCO3 (1.60 g), and the solvents were
removed under vacuum. The residue was extracted with
absolute benzene. Concentration of the combined extracts
gave 1 (881 mg, 9.2 mmol, 92%) as a light yellow oil, which
crystallized rapidly under vacuum. The crystals liquefy at r.t.
(mp 32.5 °C).2 1H NMR (250 MHz, C6D6): d = 5.88 (d,
J = 6.4 Hz, 2 H, 3-H, 5-H), 6.58 (d, J = 6.3 Hz, 2 H, 2-H, 6-
H) ppm. 13C NMR (62 MHz, C6D6): d = 118.6 (C-2, C-5),
154.6 (C-3, C-6), 176.5 (C-4) ppm.
(5) Sheldrake repeated a modification employing copper
powder and quinoline, which required a reaction
temperature of 207 °C. For details see: De Souza, C.;
Hajikarimian, Y.; Sheldrake, P. W. Synth. Commun. 1992,
22, 755.
(6) Neelakantan, L. J. Org. Chem. 1957, 22, 1584.
Synlett 2005, No. 1, 123–124 © Thieme Stuttgart · New York