RESTRICTION OF THE INVERSION PROCESS OF THE 1,3-BRIDGED RING IN THE RIGID CONFORMER OF L-2,17-DITHIA[3.3](2,2')BIPHENYLENO(1,3)CYCLOPHANE

The title compound 3 was prepared via a cyclization reaction between t wo known precursors. It is confirmed that the inversion process of the 1,3-bridged ring in the 2,17-dithia[3.3](2,2)biphenyleno(1,3)cyclopha ne system was restricted with a conformational energy barrier of >84 k J mol(-1) The adopted rigid conformation is represented by 3a (or 3b) having the methyl protons located above the cavity of one of the benze ne rings. This is consistent with the preferred conformation derived f rom semiempirical molecular orbital PM3 calculations. An the protons i n this rigid conformer could be assigned by its COSY spectra and resul ts from a series of NOE experiments. (C) 1997 Published by Elsevier Sc ience Ltd.