Reduction of the indole-1-carboxaldehydes (1a-1f) with borane /THF gives the 1-methylindoles (4) in 42-91-% yields together with the di(indolylmethyl)ethers (8), the indolyl-methyl indolines (7), the unsymmetric ether(10) and the indolenine (11) as the minor products, except 7a. This appears to be the first report on the formation of symmetric ethers in the borane/THF reduction of an oxygen function. The formation of 7a and 7b from 1a and 1b implies that electrophilic substitution takes place primarily at position 3 of 3-substituted indoles, 1c - 1f did not form the corresponding 7 probably because of steric hindrance. These results are discussed in relation to the mechanisms of borane/THF reduction, origin of the different products and electrophilic substitution in 3-substituted indoles. © 1984.

K M BISWAS

R DHARA

S ROY

H MALLIK

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

&nbsp;

The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

&nbsp;

It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Diborane as a reducing agent - VI the novel reduction of indole-1-carboxaldehydes to 1-methyl- indoles, di(indolyimethyl) ethers and indolylmethyl indolines

Tetrahedron

The number of carbons represented by each signal of the phenylindoles 1, 4, and 5 is measured quantitatively by integration of their 13C NMR spectra, recorded after adding chromium(III) acetylacetonate to the sample solutions as a paramagnetic relaxation agent. Their carbon chemical shifts are assigned unambiguously; the literature assignments of 4 are confirmed. By a comparative study of the carbon chemical shifts of 1,4, and 5, those of 2 and 3 are also assigned. The ortho carbons of the phenyl group of 4 resonate upfield with respect to the para carbon. The ortho carbons of the 2- and 3-phenyl moieties of 1 3 and 5, however, are found to absorb downfield from the corresponding para carbons, probably because of steric and/or electronic effects exerted by their neighbouring phenyl group.

Monatshefte für Chemie - Chemical Monthly

Nuclear Magnetic Resonance VI[1]. Some Quantitative Applications of Carbon-13 NMR Spectroscopy to Phenylindoles

13C signal assignments of 3‐ethyl‐1‐methylindole (1), 1‐methyl‐3‐phenylindole (3), 1,3‐dimethyl‐2‐phenylindole (5), 1‐methyl‐2,3‐diphenylindole (10), 1,5‐dimethyl‐2,3‐diphenylindole (12), 7‐methoxy‐2,3‐diphenylindole (13), 7‐methoxy‐4‐methyl‐2,3‐diphenylindole (14) and 1‐(7‐methoxy‐4‐methyl‐2,3‐diphenyl‐6‐indolyl)‐1‐(7‐methoxy‐2,3‐diphenyl‐4‐indolyl)methane (15) are reported. Contrary to an earlier report on monophenylindoles, the para carbons of the phenyl groups of 3, 5, 10 and 12–15 resonate at lower frequencies than their ortho carbons. The methoxy carbon at position 7 in 15 absorbs at a higher frequency than other similar carbons in 13–15 owing to steric inhibition to resonance. Copyright © 1985 John Wiley &amp; Sons, Ltd.

Magnetic Resonance in Chemistry

Nuclear magnetic resonance IIIâ€13C NMR spectral studies on substituted indoles

Treatment of N-acyltryptamines [3-(2-amidoethyl)indoles] with trifluoroacetic anhydride or pentafluoropropionic anhydride affords spirocyclic indolines from intermediate indolenines.

Journal of the Chemical Society, Chemical Communications

Cyclisation of N-acyltryptamines to spirocyclic indolines

Attempted reduction of N-formyl-3-methylindole (1a) and 2,3-dimethyl-N-formylindole (1b) with complex metal hydrides leads to skatole and 2,3-dimethylindole, respectively. Diborane reduction of indole derivatives has furnished interesting results.1,2 Further studies with this reagent are now reported. Diborane reduction of 1a gives 1,3-dimethylindole (4a, 49.4%) and 1,3-dimethyl-3-(3′-methylindolyl-1′-methyl)indoline (6a, 35.8%). Similarly, reduction of 1b with diorane affords 1,2,3-trimethylindole (4b, 52.4%) and two diastereoisomeric 1,2,3-trimethyl-3- (2′,3′-dimethylindolyl-1′-methyl)indolines (6b, 36.7%, and 6c, 6.8%). This appears to be the first report on the successful reduction of an N-acylindole to the corresponding N-alkyl derivative. The formation of the indolylmethylindolines (6) in the diborane reduction of N-formylindoles (1) implies that electrophilic substitution takes place primarily at the 3 position of 3-substituted indoles. These results are discussed in the light of the mechanisms of diborane reduction and electrophilic substitution in 3-substituted indoles. © 1975, American Chemical Society. All rights reserved.

Journal	Tetrahedron
Publisher	-
ISSN	0040-4020