Conformational Diagnosis of Diethyl (4S,5S)-4,5-Bis(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 (4S,5S)-4,5-bis(tert-butyldimethylsiloxy)-2E,6E-octadienedioate (1) experimentally, some appropriate reactions of 1 and its derivative (S,S)-3, which bears isopropylidene protecting groups, have been executed. The stereochemical outcomes of such reactions as the Diels-Alder reaction, osmium tetraoxide-catalyzed hydroxylation, conjugate addition with amines, and cyclopropanation with phosphonium ylides point to a rigid conformation (1A) in which the vicinal TBDMSO groups, the most bulky substituents, are arranged in an anti relationship, and, therefore, the enoate groups are forced to be gauche each other. A dichroic exciton chirality study has also provided clear-cut evidence for this rigid conformation.