7-broMo-2-Methyl-1H-Indene synthesis

Yield: 100 g (93%)

Reaction Conditions:

with sodium tetrahydroborate;pTolSO₃H in THF-methanol;toluene

Steps:

3 7-Bromo-2-methyl-1H-indene
7-Bromo-2-methyl-1H-indene To a solution of 116 g (0.52 mol) of 4-bromo-6-chloro-2-methyl-1-indanone in 950 ml of THF-methanol (2:1, vol.), 38.3 g (1.02 mol) of NaBH₄ were added in small portions for 2 h at -5° C. (Caution: temperature must be lower 0° C.). The mixture was stirred overnight at ambient temperature. The resulting mixture was poured on 1000 cm³ of ice and acidified with 10% HCl to pH=4. The organic layer was separated and the aqueous layer was extracted with 3*300 ml of methyl-tert-butyl ether. This combined extract was dried over K₂CO₃ and evaporated to dryness. To the residue 1500 ml of toluene were added and the resulting toluene solution was treated with catalytic amount of ^pTolSO₃H (ca. 2 g) for 2 h at reflux. Then this mixture was cooled to room temperature and passed through a short Silica Gel 60 column (40-63 μm, d 60 mm, 1 40 mm). This column was additionally eluted with 250 ml of toluene. The combined extract was evaporated to dryness. Fractional distillation gave a mixture of the title indenes, b.p. 104-108° C./5 mm Hg. Yield 100 g (93%) of colorless solid. Anal. calc. for C₁₀H₉Br: C, 57.44; H, 4.34. Found: C, 57.59; H, 4.40. ¹H NMR (CDCl₃): δ 7.23 (dd, J=7.9 Hz, J=1.0 Hz, 1H, 6-H), 7.18 (dd, J=7.4 Hz, J=1.0 Hz, 1H, 4-H), 7.10 (m, 1H, 5-H), 6.51 (m, 1H, 3-H), 3.28 (m, 2H, 1,1'-H), 2.17 (s, 3H, 2-Me). ¹³C NMR (CDCl₃): δ 147.3, 146.8, 143.3, 128.2, 127.1, 126.6, 118.7, 118.3,44.2,16.7.

References:

Voskoboynikov, Alexander Z.;Ryabov, Alexey N.;Nikulin, Mikhail V.;Lygin, Alexander V.;Coker, Catalina L.;Canich, Jo Ann M. US2007/135595, 2007, A1