859196-82-0Relevant articles and documents
Conformational Analysis of 1- and 3-Isopropylindoles. A 1H NMR and Molecular Mechanics Study
Nilsson, Ingemar,Berg, Ulf,Sandstroem, Jan
, p. 491 - 500 (2007/10/02)
The conformations of the isopropyl groups in a series of 1- and 3-isopropylindoles have been studied by 1H NMR and molecular mechanics technique.The isopropyl group is shown to assume both syn and an anti conformation, and the equilibrium between these is shown to depend on the steric size of the substituent in position 2.The syn form is relatively more favoured in the 3- than in the 1-isopropylindoles, which can be explained by differences in the lengths of the ring bonds to N-1 and C-3.The energy barriers to syn-anti exchange are 45-46 kJ mol-1 in the 1-iPr compounds when R2=Me or CO2Me.This barrier is lower in the 3-iPr analogues and could only be measured when R1=iPr, R2=Me (35 kJ mol-1).In the 1-iPr compounds a 3-Me group exerts no observable buttressing effect on a 2-Me group, unlike the situation in 1-iso-propylnaphthalenes, where introduction of a 3-Me group leads to an apparent diminution of the steric effect of the 2-Me group ("negative buttressing").In 1-isopropyl-2-methylindole a 3-Br also exerts a negative buttressing effect.