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The synthesis of 1-formyl-2-(3-indolyl)-4-piperidone, trans-1-formyl-2-(3-indolyl)-3-methyl-4-piperidone, and their 4,4-ethyleneacetals is described. The introduction of a formyl group on the piperidone nitrogen induces a change in the piperidine ring conformation such that the 2-indolyl group is axial. However, in the 1-formyl-2-indolyl-4-piperidone 4,4-ethyleneacetals the indolyl group adopts an equatorial disposition due to a severe steric syn-diaxial interaction with the C-4 substituent. 13 C-Dnmr is used to investigate the amide rotational barriers in a series of 2-aryl-1-formyl-4-piperidones