Cyclohexanone Derivatives : Synthons for Substituted Quinolines

Abstract

Substituted quinolines 4, S, and 9 were reported from o-allyl ethers of cyclohexanone derivatives by [2,3] sigmatropic rearrangement followed by cyclization. All the new compounds were characterized by 1R and 'H NMR spectra.Brought to you by | Purdue University Libraries Authenticated Download Date | 5/29/15 7:32 PM Vol. 7, No. 5, 2001 Cyclohexanone derivatives: synthons for substituted quinolines ExperimentalMelting points were determined in open capillaries on Tempo Mel-Temp apparatus and arc uncorrected. The purity of the compounds was checked by thin layer chromatography (silica gel-G, BDH), pet. ether (40-60°C): ethyl acetate (3:1) as eluents). The 1R spectra were recorded on a Perkin-Elmer Infrared spectrometer (v nux in cm" 1 ) model 337 in KBr pellets. The 'H NMR spectra were recorded in CDC1, 200 MHz on Bruker spectrospin and Varian LiM-360 spectrometers with TMS as an internal standard (Chemical shifts in δ ppm).Microanalyses were performed by Microanalytical laboratory, University of Pune, Pune, India.3,5-Diaryl-2-cyclohexenone (1) and 3,5-diarylcyclohexanone (6) were prepared according to literature procedures. 7 ' 8 Preparation of Oxime of 3,5-diaryl-2-cyclohexenone (2a-c) / 3,5-diaryl-cycIohexanone (7a-c)Λ solution of 3,5-diarylcyclohexenone (2) / 3,5-diarylcyclohexanone (6) (0.01 mol), hydroxylamine hydrochloride (0.69 g, 0.012 mol) and a catalytic amount of triethylamine in ethanol was refluxed on a water bath for 1-2 hrs. The contents were concentrated and cooled The product separated was filtered and dried. It was recrystallized from ethanol to gel pure 2/7. Preparation of O-allyl ether of 3,5-diaryl-2-cycIohexenone oxime (3a-c)/ 3,5-diarylcycIohexanone oxime (8 a-c).A mixture of 2/7 (0.01 mol) and allyl bromide (1.43 g, 0.02 mol) in methanol was cooled at ice-salt bath temperature. To this, a solution of sodium hydroxide (3 g) in methanol (60 mi) was added and refluxed for 3-4 hrs. The reaction mixture was cooled, the precipitated NaBr was removed by filtration and the filtrate was concentrated. The resultant viscous mass was solidified by heating with hexane and filtered through a column of silica gel to obtain pure 3/8. Preparation of 5,6-dihydro-5,7-diarylquinoIine (4a-c) / 5,6,7,8-tetrahydro-5,7-diaryl- quinoline (9a-c)A solution of 3/8 (0.003 mol) in dry benzene (10 ml) was taken in a pyrex sealed tube under nitrogen atmosphere and heated at 200°C in an oil bath for two days. It was cooled and opened. The contents were transfered and benzene was removed under reduced pressure. The semi-solid obtained was subjected to column chromatography to get pure 4/9. Preparation of 5,7-diaryiquinoline (5a-c).A 1:1.5 molar mixture of 4/9 and DDQ in dry benzene (20 ml) was heated at reflux temperature for 2 hrs under nitrogen atmosphere. The precipitated DDQ-H 2 was filtered off Brought to you by | Purdue University Libraries