| Molbank 2004, M380 |
Lajos Kov¨˘cs1, *, P¨¦ter Forg¨®2, Zolt¨˘n Kele1 and Éva Klement1
1Department of Medicinal
Chemistry
2Department of Organic Chemistry, University of Szeged,
D¨®m t¨¦r 8, H-6720 Szeged, Hungary. Fax: +36-62-54 59 71
*E-mail: [email protected]
Received: 16 October 2003 / Accepted: 17 March 2004 / Published: 29 March 2004
In our previous work we have demonstrated the utility of the 2,2,2-trichloro-1,1-dimethylethyl (b,b,b-trichloro-tert-butyl, Tcb) group for the protection of carboxylic acids [1]. Herein we would like to describe the preparation of one of their representatives, the title aromatic ester. The procedure applied by us is based on the work by Gupta and Srivastava [2].
Experimental: Freshly prepared anhydrous zinc chloride (0.41 g, 3.0 mmol) was chilled in an ice-bath (0-5 ˇăC), then 4-tert-butylbenzoyl chloride (2.73 mL, 2.95 g, 15.0 mmol) and anhydrous b,b,b-trichloro-tert-butanol (1.775 g, 10.0 mmol, prepared by in vacuo drying of the commercial hemihydrate over phosphorus pentoxide) were added, each in one portion. The flask was removed from the ice-bath and gently shaken to initiate the evolution of hydrogen chloride. When the gas evolution had subsided the reaction mixture was heated at 100 ˇăC for 2 h. The mixture was diluted with diethyl ether (100 mL), washed with cold satd. NaHCO3 solution (3 x 50 mL) and brine (50 mL), respectively. The organic phase was dried (MgSO4) and evaporated. The oily residue solidified upon standing (2.756 g, 82%, TLC: single spot). An analytical sample was obtained by recrystallization from methanol (14 mL).
Mp. 78.7-79.8 ˇăC.
TLC: light petroleum-ethyl acetate 7:3, Rf: 0.76.
Anal. calcd. for C15H19Cl3O2 (337.669): C, 53.35; H, 5.67; Cl, 31.50%; found C, 53.48; H, 5.78; Cl, 31.29%.
IR (n, cm-1, CHCl3, KBr): 705m, 789m, 806m, 856w, 1016w, 1119s, 1193m, 1284s, 1370w, 1387w, 1410w, 1462w, 1606w, 1722s (nC=O), 2871w, 2905w, 2967m.
1H NMR (CDCl3, 500 MHz, ppm): 1.34 (s, 9H, tert-Bu), 2.03 (s, 6H, (CH3)2C), 7.48 (d, 2H, J=8.5 Hz, arom. CHs), 8.00 (d, 2H, J=8.5 Hz, arom. CHs).
13C NMR (CDCl3, 125 MHz, ppm, assignment based on HMBC and HMQC experiments): 21.42 ((CH3)2CCCl3), 31.09 ((CH3)3C), 35.11 ((CH3)3C), 88.97 (CCl3), 107.12 ((CH3)2CCCl3), 125.47 (arom. CHs), 127.89 (arom. quaternary C), 129.74 (arom. CHs), 156.99 (arom. quaternary C), 164.46 (COO).
CI-MS (isobutane, m/z): 341, 339, 337 ([M+H]+, isotopic peaks); 305, 303 ([M-Cl]+, isotopic peaks). The calculated peak distributions correspond to the expected structure.
References:
1. L. Kov¨˘cs, P. Forg¨®, Z. Kele: Fourth International Electronic Conference on Synthetic Organic Chemistry, abstr. no. a0076 (http://www.unibas.ch/mdpi/ecsoc-4/a0076/a0076.htm).
2. I. Gupta, N. P. Srivastava: Recl. Trav. Chim. Pays-Bas, 1956, 75, 48-50.
Sample availability: sample available from the authors.
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