Interactions intramoleculaires. XIV. Interactions gauches avec un groupement t-butyle (séries cyclohexanique et cyclohexénique)

Abstract

For the 4-substituted (X = COOC2H5 or C≡N) and 4,5-disubstitued (X = COOC2H5) 3-t-butyl cyclohexenes, their saturated homologs and for 1,2-dimethyl 4-methoxycarbonyl 5-t-butyl cyclohexene, the free energy differences are determined and discussed in terms of gauche interaction differences.For disubstitued cyclohexane compounds, (Iae – Iee) values are +0.2 (X = COOC2H5) and −1.7 kcal mol−1 (X = C≡N) for interactions with a vicinal t-butyl group; in the last case, the axial cyano isomer is clearly more stable than the equatorial cyano isomer.For disubstitued cyclohexene compounds, (Iae – Iee) values are +2.1 (X = COOC2H5) and +6 kcal mol−1 (X = C≡N).For trisubstitued compounds, the results can be explained by an increase of diequatorial interactions in all equatorial stereoisomers.The synthesis and the isomer identifications are reported.