Conformational Studies of Selectively Methylated [2.2](1,3)(1,4)Cyclophanes. Steric Effects in the Relative Conformational Ground States

Yee Hing Lai, Angeline Hui Tin Yap, Igor Novak

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7 Citations (Scopus)

Abstract

Three selectively methylated [2.2](1,3)(1,4)cyclophanes, namely, 12,15-dimethyl-,12,16-dimethyl-, and 12,13,14,15-tetramethyl[2.2](1,3)(1,4)cyclophanes, were synthesized from their corresponding dithia[3.3] (1,3)(1,4)cyclophanes by the photochemical desulfurization method. Dynamic 1H NMR spectroscopy was employed to estimate the relative conformational barrier in each [2.2]cyclophane. The results show that there is an increase of about 13 kJ mol-1 going from the parent [2.2] (1,3)-(1,4)cyclophane to its 12,15- and 12,16-dimethyl derivatives. This is consistent with the fact that the presence of the methyl substituents increases the relative conformational ground-state energy more than it would affect the transition-state energy. The conformational barrier of the 12,13,-15,16-tetramethyl derivative was unexpectedly found to be similar to those of the two dimethylated derivatives. This however could be explained by a decrease in the transition-state energy due to inward bending of the (1,4)-bridged ring accompanied by a decrease in conformational ground-state energy due to outward bending of the methyl groups.

Original languageEnglish
Pages (from-to)3381-3385
Number of pages5
JournalJournal of Organic Chemistry
Volume59
Issue number12
DOIs
Publication statusPublished - 01 Jun 1994

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