REFERENCES
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- A typical procedure for cyclization step is: l g of 1 was added to 20 cm3 concentrated sulphuric acid (R1 = H, R2 = CH3: 0°C, 10 min.; R1 = CH3, R2 = H: 0°C, 4 h). The reaction mixture was poured over 100 g of ice and extracted with diethyl ether. The organic layer was washed with water, dried (Na2SO4), and evaporated under reduced pressure. The residue was purified by recrystallization from ether (R1 = H, R2 = CH3) or by flash chromatography eluting with 80/20 CH2Cl2/CH3OH and recrystallization from ether (R1 = CH3, R2 = H). 2a. White crystals (75%) F: 152°C. Anal. calc. For C13H12O4: C, 67.23; H, 5.21; O, 27,56. Found: C, 67.08; H, 5.38; O, 27.66. IR (KBr) vCO 1765, 1720 cm−1. 1H NMR (400 MHz, CDCl3): 7.28 (m, 4H, H4,5,6,7); 4.13 (d, 1H, J = 3.3, H3); 3.78 (d, 1H, J = 3.3, H3a); 3.49 (d, 1H, J = 17.6, H8); 3.25 (d, 1H, J = 17.6, H8′); 1.77 (s, 3H, CH3). 13C NMR: 170.8 (COOH); 168.8 (C˭O); 142.4, 140.5, (C3b,7a); 128.6, 128.0, 125.3, 125.2 (C4,5,6,7); 93.6 (C8a); 54.9, 54.7 (C3,3a); 45.2 (C8); 24.8 (CH3). 3a. White crystals (65%) F: 104°C. Anal. calc, For C13H12O4: C, 67.23; H, 5.21; O, 27,56. Found: C, 67.16; H, 5.25; O, 27.61. IR (KBr) vCO 1746, 1715 cm−1. 1H NMR (400 MHz, CDCl3): 7.46–7.40 (m, 5H, H8,9,10,11); 5.49 (dd, 1H, J = 12.4, J′ = 3.6, H5); 3.08 (dd, 1H, 1H J = 19.0, J′ = 12.4, H6); 2.85 (dd, 1H, J = 19.1, J′ = 3.6, H6′); 2.61 (s, 3H, CH3). 13C NMR: 172.8 (COOH); 167.6 (C = O); 162.9 (C3); 136.2 (C4); 130.0 (C10); 129.3, 129.0 (C8,12 and C9,11); 77.8 (C5); 40.6 (C6); 23.8 (CH3)
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- Howell , J. A.S. , O'Leary , P. J. , Yates , P. C. , Goldschmidt , Z. , Gottlieb , H. E. and Hezroni-Langerman , D. 1995 . Tetrahedron , 51 : 7231
- Deno , N. C. , Pittman , C. U. Jr. and Turner , J. O. 1965 . J. Am. Chem. Soc. , 87 : 2153