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Stereoselectivity of the Ortho Ester Claisen Rearrangement of Substituted Silylpropargylic Alcohols
Stereoselectivity of the Ortho Ester Claisen Rearrangement of Substituted Silylpropargylic Alcohols
Journal of the Korean Chemical Society. 2004. Aug, 48(4): 439-442
Copyright © 2004, The Korean Chemical Society
  • Received : January 26, 2004
  • Published : August 20, 2004
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성준 윤
근회 정
병찬 유

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EXPERIMENTAL SECTION
- The typical procedure of the preparation of the ynols and the ortho ester Claisen rearrangement
1-Cyclohexyl-3-trimethylsilanyl-prop-2-yn-1-ol (2f). To a solution of 1.00 g (0.01 mmol) of trimethylsilylacetylene in 30 mL of THF was added 4.3 mL (0.011 mol) of 2.5 M n-BuLi in hexanes at -78 ℃ dropwise. The solution was stirred for 1 hr and 1.3 mL (0.011 mol) of freshly distilled cyclohexanecarboxaldehyde was added in one portion. The mixture was stirred for 1 hr and then allowed to warm to room temperature. Water was added. The organic layer was separated and extracted with ether three times. The extracts were dried over MgSO 4 and concentrated under reduced pressure. The residue was chromatographed on silica gel with 5% ether in hexanes. Concentration gave 1.95 g (91%) of 2f: IR (neat) 3341, 2926, 2853, 2667, 2171, 1450, 1407, 1379,1250, 1084, 1032 cm −1 ; 1 H NMR (300MHz, CDCl 3 ) 3.95 (1H, d, J=6.0 Hz, methine H), 2.80-1.80 (12H, m, hexyl Hs and OH), 0.12 (9H, s, Si(CH 3 ) 3 ) ppm; 13 C NMR (200MHz, CDCl 3 ) 105.8, 90.1, 67.5, 50.0, 43.9, 28.4, 28.0, 26.4, 25.9, 0.01(3).
rel-(2S,4R)-5-Cyclohexyl-2-methyl-3-trimethylsilanyl-penta-3,4-dienoic acid ethyl ester(3f). To 500 mg (2.38 mmol) of the propargylic alcohol 2f was added 3.40 mL (16.7 mmol) of triethyl orthopropionate and 11 mg (0.14 mmol) of propionic acid. The solution was stirred for 5 hrs at 80 ℃. The ratio of the diastereomeric allenic esters was determined by GC analysis (93:7). Ethanol and the excess ortho propionate were removed under reduced pressure. The residue was chromatographed on silica gel with 1% and 2% ether in hexanes to give 470 mg (67%) of allenic ester 3f: IR (neat) 2926, 2853, 2178, 1937, 1736, 1449, 1248, 1177, 1100, 841 cm −1 ; 1 H NMR (200MHz, CDCl 3 ) δ 5.00 (1H, brt, vinyl H), 4.11 (2H, q, J=7.1 Hz, -OCH 2 CH 3 ), 3.0 (1H, m, methine H), 1.00-2.00(14H, CH 3 CH- and hexyl Hs), 1.27 (3H, t, J=7.1 Hz, -OCH 2 CH 3 ), 0.11 (9H, s, -Si(CH 3 ) 3 )ppm; 13 C NMR (80MHz, CDCl 3 ) δ 205.4, 172.0, 128.4, 98.4, 94.7, 60.3, 40.0, 36.8, 33.4, 33.3, 26.2, 17.4, 14.1, 1.1(3); FAB+ mass m/z 294.1.
Acknowledgements
Acknowledgement. We would like to thank Sung-Kon Kim of KRICK for the assistance of NMR spectra.
References
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