3022
R. Ahmad et al. / Tetrahedron Letters 50 (2009) 3020–3022
8. Winkler, J. D.; Oh, K. Org. Lett. 2005, 7, 2421.
The structures of all products were established by spectroscopic
9. Gao, B.; Yua, Z.; Fua, Z.; Fenga, X. Tetrahedron Lett. 2006, 47, 1537.
10. Wang, H.; Shuhler, B. J.; Xiang, M. J. Org. Chem. 2007, 72, 4280.
11. Light, R. J.; Hauser, C. R. J. Org. Chem. 1961, 26, 1716.
methods. The structure of 5a was independently confirmed by
X-ray crystal structure analysis (Fig. 1).17
12. For a review of cyclization reactions of dianions, see: Langer, P.; Freiberg, W.
Chem. Rev. 2004, 104, 4125.
In conclusion, a variety of 6-aryl-2,3-dihydro-4H-pyran-4-ones
were prepared in one step by cyclocondensation of 1,3-diketone
dianions with aldehydes and subsequent work-up using hydro-
chloric acid (10%). We currently study the preparative scope and
synthetic applications of the methodology reported.
13. Ansell, J. M.; Hassner, A.; Burkholder, W. E. Tetrahedron Lett. 1979, 2497.
14. Peterson, J. R.; Winter, T. J.; Miller, C. P. Synth. Commun. 1988, 18, 949.
15. Typical procedure: synthesis of 2-methyl-6-phenyl-2,3-dihydro-4H-pyran-4-one
(5a). A THF Solution of LDA (25.0 mmol) was prepared by addition of nBuLi
(10 mL, 25.0 mmol, 2.5 M solution in hexanes) to a THF solution (30 mL) of
diisopropylamine (2.52 g, 25.0 mmol) at 0 °C. After stirring for 1 h, the solution
was cooled to À78 °C and 2,4-pentadion (1.00 g, 10.0 mmol) was added. After
stirring for 1 h at À78 °C, benzaldehyde (1.06 g, 10.0 mmol) was added and the
solution was allowed to warm to 20 °C within 24 h. Hydrochloric acid (10%,
25 mL) was added and the mixture was allowed to stand for 15 min. Ethyl
acetate (25 mL) was added. The organic and aqueous layers were separated
and the latter was extracted with ethyl acetate (3 Â 50 mL). The combined
organic layers were dried (Na2SO4), filtered, and the filtrate was concentrated
in vacuo. The residue was purified by chromatography (silica gel, heptanes/
ethyl acetate = 2:1) to give 5a as a colorless crystalline solid (1.63 g, 87%), mp
45–48 °C. 1H NMR (250 MHz, CDCl3): d 1.98 (s, 3H, CH3), 2.47–2.55 (dd, 1HA,
J = 3.2, 16.7 Hz), 2.66–2.79 (dd, 1HB, J = 14.0, 16.7 Hz), 5.27–5.34 (dd, 1H, CH,
J = 3.2, 14.5 Hz), 5.36 (s, 1H, CH), 7.28–7.33 (m, 5H, Ph). 13C NMR (300 MHz,
CDCl3): d 21.1(CH3), 42.4 (CH2), 80.8, 105.2 (CH), 126.1, 128.8 (CHAr), 138.1,
174.3, 192.3 (C). IR (KBr): v 3062, 3033, 2962, 2918 (w), 1661, 1603, 1392, 1327
(s), 1237, 1179, 1023 (m), 999 (s), 950, 808 (m), 755, 696 (s) cmÀ1. MS (EI,
70 eV): m/z (%) 188 (M+, 2), 170 (8), 155 (6), 145 (36), 104 (100), 91 (2), 78 (16),
77 (12). HRMS (ESI-TOF): calcd for C12H13O2 [M+H]+: 189.09101; found:
189.09077.
16. (a) Fluorine in Bioorganic Chemistry; Filler, R., Kobayasi, Y., Yagupolskii, L. M.,
Eds.; Elsevier: Amsterdam, 1993; (b) Filler, R. Fluorine Containing Drugs in
Organofluorine Chemicals and their Industrial Application; Pergamon: New York,
1979. Chapter 6; (c) Hudlicky, M. Chemistry of Organic Compounds; Ellis
Horwood: Chichester, 1992; (d) Kirsch, P. Modern Fluoroorganic Chemistry;
VCH: Weinheim, 2004; (e) Chambers, R. D. Fluorine in Organic Chemistry;
Blackwell Publishing CRC Press, 2004.
17. CCDC 719665 contains all crystallographic details of this publication and is
ordered from the following address: Cambridge Crystallographic Data Center,
12 Union Road, GB-Cambridge CB21EZ; Fax: (+44)1223-336-033; or
Acknowledgment
Financial support from the State of Pakistan (HEC scholarship
for R.A.) is gratefully acknowledged.
References and notes
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