Issue in Honor of Prof. S. Swaminathan ARKIVOC 2005 (xi) 218-225
Experimental Section
General Procedures. The compounds described here are all racemates. IR spectra were recorded on Perkin-Elmer model PE 298 and Shimadzu FTIR- 8300 spectrophotometers. Unless otherwise stated, 1H and 13C NMR spectra were recorded in CDCl3 solution at 300 MHz and 75 MHz respectively on a Bruker DPX-300 spectrometer with SiMe4 as internal standard. Moisture sensitive reactions were carried out using standard syringe-septum technique. Anhydrous solvents were obtained by standard procedures. All solvent extracts were dried over anhydrous Na2SO4. Product purities were routinely checked by TLC. Ether refers to diethyl ether and light petroleum refers to the fraction of petroleum ether in the boiling point range 60 – 800C.
1,1,4-Trimethyl-6-methoxyindane (5). To a stirred suspension of MeMgI [prepared from magnesium turnings (5.3 g, 0.22 g-at.) and MeI (32 g, 0.225 mol)] in anhydrous ether (70 mL) was added slowly under nitrogen a solution of the ester 4 (10 g, 0.048 mol) in ether (20 mL). The mixture was stirred at room temperature for 30 min and then refluxed for 5 h. It was then cooled in an ice-bath and decomposed carefully with saturated aqueous NH4Cl (60 mL). The organic layer was separated and the aqueous phase extracted with ether (2x30 mL). The combined ether solution was washed with water (2x30 mL) and dried. Evaporation of the solvent furnished the crude product as an oil (10 g) [IR (film) 3404, 2968, 1608, 1502 cm -1 ; 1H NMR d 1.29 (s, 6H, CMe2), 1.62-1.70 (m, 2H, ArCH2CH2), 2.37 (s, 3H, ArMe), 2.58-2.64 (m, 2H, ArCH2CH2), 3.75 (s, 3H, ArOMe), 6.65-6.70 (m, 2H, ArH), 7.04 (d, 1H, J = 8.1 Hz, ArH); 13C NMR d 19.4, 27.2, 29.1, 44.7, 55.1, 70.8, 111.0, 115.8, 129.4, 132.7, 136.9, 157.6] which was cyclised by heating with polyphosphoric acid [prepared by heating at 95-1000C for 2 h a mixture of P2O5 (80 g) and H3PO4 (89%, 35 mL)] at 900C for 1 h. The reaction mixture was cooled, decomposed with crushed ice, and extracted repeatedly with ether. The combined ether extract was washed successively with water, saturated aqueous NaHCO3 until alkaline, water again until neutral, and then dried. Removal of the solvent followed by distillation of the residue at 105-108oC (bath temp.) / 0.8 mm Hg furnished the indane 5 (6.58 g, 72%) as a colourless oil; 1H NMR d 1.23 (s, 6H, CMe2), 1.91 (t, 2H, J = 7 Hz, ArCH2CH2), 2.22 (s, 3H, ArMe), 2.72 (t, 2H, J = 7 Hz, ArCH2CH2), 3.77 (s, 3H, ArOMe), 6.53 (bs, 2H, ArH); 13C NMR d 19.2, 27.8, 28.6, 28.7, 41.4, 44.2, 55.3, 105.1, 112.7, 133.5, 134.5, 153.8, 159.1. Anal. Calcd. for C13H18O : C, 82.06; H, 9.53. Found: C, 82.22; H, 9.59%. 3,3,7-Trimethyl-5-methoxyindan-1-one (6). A solution of CrO3 (6 g, 0.06 mol) in 80 % aqueous AcOH (30 mL) was added slowly with stirring to a solution of the indane 5 (6.3 g,
0.033 mol) in glacial AcOH (40 mL) at 50C. After the addition, the mixture was stirred at 100C for 5 h, allowed to stand at room temperature for 12 h and then diluted with water (70 mL). Solid Na2CO3 was added in portions to neutralise most of the acetic acid and the product was extracted with ether (3x50 mL). The combined ether extract was washed with aqueous NaHCO3 and water, dried and concentrated. The residue was distilled to furnish the indanone 6 (4.94 g, 73 %) as a colourless oil, b.p. 138 – 1400C (bath temp.) / 0.6 mm Hg; IR (film) 1697, 1598 cm-1; 1H NMR d ISSN 1551-7004 Page 221 ©ARKAT USA, Inc
