Anomalous1H NMR spectra of 3,4-dihydroisoquinolines and related compounds |
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| Authors: | S Narayanaswami S Rajeswari B R Pai K Nagarajan W J Richter and S J Shenoy |
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| Institution: | (1) Department of Chemistry, Presidency College, 600 005 Madras, India;(2) Research and Development Laboratories, Amrutanjan Limited, 600 004 Madras, India;(3) Present address: Pfizer Corporation, Sandwich, England;(4) Present address: Hindustan CIBA-GEIGY Research Centre, 400 063 Bombay, India;(5) Present address: CIBA-GEIGY Limited, Basel, Switzerland |
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| Abstract: | Solutions of 3,4-dihydro-6,7-methylenedioxyisoquinoline (1) and analogues2–5 and9 as well as isoquinolines7 and8 in certain samples of CDCl3, CCl4, DMSO-d6 or acetone-d6 gave rise to anomalous1Hnmr spectra with extreme line broadening, signals due to protons at C-l and C-3 most often not being seen. The spectra of1 and3 were most striking in this respect.1Hnmr spectra of the quaternary salt10 and the model schiff base11 were normal. Several hypotheses for the observed line broadening have been considered and rejected, a slow equilibrium1 ⇆13 being one of them. NaBH4 reduction of1 and2 followed by mass spectrometric analysis of the crude tetrahydroisoquinolines16 and17 ruled out a slow equilibrium1 ⇆14 and2 ⇆15 as contributory cause for line broadening. The crude reduction products unexpectedly contained N-ethyl species22 and25. Their formation is rationalised |
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| Keywords: | 3 4-dihydroisoquinolines isoquinolines anomalous NMR spectra NaBH4 reduction |
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