Triflic Acid Catalyzed Cyclization of trans-Cinnamaldehyde to 3-phenyl-1H-indene
SyntheticPage 764
DOI:
Submitted: September 14, 2014, published: September 15, 2014
Authors
Ravindra Phatake (ravirajphatake@gmail.com)
Sachin Gholap (ssachingholap1890@gmail.com)
A contribution from
Chemicals
Triflic Acid
Triethyl amine
Benzene
Procedure
To a well-stirred mixture of trans-cinnamaldehyde (15 g, 1 mol.) in benzene (150 mL) at about 0 oC to -5 oC was added Triflic acid (2 ml, 0.2 mol.) in portions. After the addition of the reagent, the cooling bath was removed. The reaction mixture was stirred at 60 oC for 15 h. The resultant reaction mixture was cooled at 0 oC and quench with triethyl amine (approx 5-7 ml) followed by ice cold water and extracted with ethyl acetate (200 mL×2). The combined organic layer dried over sodium sulphate and concentrated under reduced pressure. The residue was flash chromatographed (the eluent was pet ether) to give 20 g (92 %) of 3-phenylindene.
Author Comments
This reaction has been carried out at number of time by graduate trainees. The reaction seems to be ideal for gram scale (87-92%). Triflic acid addition should not go beyond -5 oC to 0 oC (some time decomposition of reaction mixture happening). Excess amount of triflic acid addition decreasing the yield, quenching with triethyl amine gives a clean reaction mixture if we pour direct it in ice water it will form back colored emulation.
Data
1H NMR (200 MHz, CDCl3): δ = 3.51 (d, J = 2.0 Hz, 2H), 6.58 (t, J = 2.0 Hz, 1H), 7.22–7.26 (m, 1H), 7.28–7.31 (m, 3H), 7.45–7.58 (m, 2H), 7.56–7.63 (m, 3H) ppm
Lead Reference
Supplementary Information
Keywords
aldehydes, Cyclization, triflic acid