2-Methylindole → 1-Benzyl-2-methylindole

Participants

Reaction Steps

To a solution of 2.39 g (9.04 mmoles) of 18-crown-6 in 250 mL of dry ether was added 13.1 g (116.7 mmoles) of potassium tert-butoxide. The mixture was stirred while 13.11 g (100 mmoles) of 2-methylindole was added. The stirring was continued for 0.5 hour. Most of the solid dissolved. Then 20 g (116.9 mmoles) of benzyl chloride in 120 mL of ether was added during 45 minutes. The stirring was continued for 21.5 hours. Water (200 mL) was added. The layers were separated. The aqueous layer was extracted with ether (2×75 mL). The combined ether phases were washed with 50 mL of brine and dried over MgSO4. Evaporation of the solvent left 25.85 g of dark brown oil. The oil was chromatographed on a 1100 g column of silica gel. The column was eluted with 25% CH2Cl2 -Skellysolve B and 200 mL fractions were collected. The fractions were assayed by silica gel tlc (1×4") (25% CH2Cl2 -Skellysolve B). Fractions 22-25 were combined giving 2.28 g (10%) of slightly impure 1-benzyl-2-methylindole as a pale yellow oil which solidified upon standing. Fractions 26-35 were combined giving 8.42 g of 1-benzyl-2-methylindole and 1,3-dibenzyl-2-methylindole as a pale yellow oil. The 8.42 g was combined with the 7.50 g of a similar mixture from fractions 23-28, and chromatographed on a 1100 g column of silica gel. The column was eluted with 25% CH2Cl2 -Skellysolve B and 200 mL fractions were collected. The fractions were assayed as before. Fractions 21-24 were combined giving 3.59 g of 1-benzyl-2-methylindole as a pale yellow oil which solidified. Fractions 25-30 were combined giving 7.66 g of a mixture of 1-benzyl-2-methylindole and 1,3-dibenzyl-2-methylindole as an oil.

Provenance & Evidence