CONFORMATIONAL DIAGNOSIS OF DIETHYL IS(TERT-BUTYLDIMETHYLSILOXY)-2E,6E-OCTADIENEDIOATE BASED ON THE STEREOCHEMICAL OUTCOMES OF REPRESENTATIVE REACTIONS AS COMPARED WITH THOSE OF ITS 4,5-O-ISOPROPYLIDENE DERIVATIVES AND ON A DICHROIC EXCITON CHIRALITY METHOD

In order to gain more insight into the conformation of diethyl is(tert -butyldimethylsiloxy)-2E,6E-octadienedioate (1) experimentally, some a ppropriate reactions of 1 and its derivative (S,S)-3, which bears isop ropylidene protecting groups, have been executed. The stereochemical o utcomes of such reactions as the Diels-Alder reaction, osmium tetraoxi de-catalyzed hydroxylation, conjugate addition with amines, and cyclop ropanation with phosphonium ylides point to a rigid conformation (1A) in which the vicinal TBDMSO groups, the most bulky substituents, are a rranged in an anti relationship, and, therefore, the enoate groups are forced to be gauche each other. A dichroic exciton chirality study ha s also provided clear-cut evidence for this rigid conformation.