Tetrahydrofuran → 7-Chloro-2-methyl-1H-indene

Participants

Reaction Conditions

Reaction Steps

A 5L round-bottom flask is equipped with a mechanical stirrer, thermometer and reflux condenser, and swept thoroughly with nitrogen. 2L tetrahydrofuran (THF) is added to the flask and then 116 g NaH, 60% dispersion in mineral oil (2.9 mol). An ice bath is applied to the flask and moderate stirring begun. 506 g methyl diethyl malonate (2.9 mol) is added slowly from an addition funnel maintaining the temperature below 10° C. Hydrogen evolution is monitored and vented through a mineral oil bubbler and controlled by the rate of addition of the methyl dimethyl malonate. Once the addition is complete, the cooling bath is removed, and the reaction stirred for 2 hours. The flask is again cooled to 5° C. and 367 mL 2-chlorobenzylchloride (2.9 mol) added over 1 hour, then stirred for 12 hours at ambient temperature. Reflux condenser is changed to short path distillation. 520 mL 50% W/v NaOH(aq) and 1500 mL H2O is added, then heating begun to distill the THF. Distillation was continued to 100° C. with additional water to keep the reaction clear and fluid. Distillation was continued to remove ethanol and water at 100° C. for 15-30 minutes. Once cooled, the reaction mixture was poured into 1.5L H2O and 1L 12N HCl with vigorous stirring. White solids, which formed immediately, were collected by filtration and dried on the Buchner funnel by aspiration for 15 minutes, then returned to the 5L flask equipped for short path distillation. Heating was applied slowly to melt the solids, and then increased to 135° C. for at least 1 hour. CO2 evolution was monitored by venting through a mineral oil bubbler. The melt was cooled to 50° C. and 2L heptane added, then warmed to 45° C., and addition of 265 mL SOCl2 (3.63 mol) was begun. Adequate venting was provided. After all the SOCl2 was added, the reaction was stirred for 1.5 hours at 60° C., then heated to 120° C. to distill the excess SOCl2 and all the heptane. The reaction flask was allowed to cool to ambient temperature and 1.5L CH2Cl2 is added. Cooling was applied to -5°-0° C., and 465 g AlCl3 (3.5 mol) added in portions. The reaction was stirred at ambient temperature for 2 hours, then quenched by pouring onto 2 Kg ice. The layers were separated, and the organic layer was washed with 500 mL H2O, and then 250 mL 5% w/v NaHCO3 (aq). All the solvent was distilled to a temperature of 70° C. 1L methanol was added to the oil, the flask cooled with an ice bath, and a slurry of 56 g NaBH4 (1.5 mol) in 500 mL methanol containing 1 g NaOCH3 was slowly added. Hydrogen evolution was monitored by venting through a mineral oil bubbler and controlled by the rate of addition. The reaction was quenched by adding 1.5L H2O and 500 mL CH2Cl2 to separate the product. Solvent was distilled from the separated organic layer up to 70° C. 1.5L toluene was added to the oil and the 5L flask equipped with a Dean-Stark trap. Heating was begun and p-toluene sulfonic acid was added in 1-3 g portions. The reaction was followed by GC until the dehydration was complete. 1.5L 5% w/v NaHCO3 (aq) was added to the reaction, the layers separated, and the organic layer dried over anhydrous Na2SO4. Toluene was distilled under reduced pressure to 90° C. and the product, 2-methyl-7-chloroindene, obtained by distillation thorough a 30 cm packed column at 93-5° C. at 1-3 mm Hg. Yield was 310 g (1.89 mol), 65%, of a clear, colorless oil b.p. 229° C. FIG. 2 was the NMR spectrum of the product.

Provenance & Evidence