Restricted Rotation Involving the Tetrahedral Carbon. XVI. Isolation of Stable Rotamers about an sp3-sp3 Carbon Bond

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Abstract
Both antiperiplanar and synclinal rotamers resulted from the restricted rotation about a C–C single bond between the bridgehead t-alkyl group and the skeleton of 9-(1,1-dimethyl-2-phenylethyl)-11-methoxycarbonyl-9,10-dihydro-9,10-ethenoanthracene-12-carboxylic acid are isolated. Optical resolution of the synclinal rotamer is successfully performed by way of the mono-(−)-menthyl esters and a pair of enantiomers of the acid, [α]D32±24.7°, are isolated as stable entities. Activation energy for the interconversion between the rotamers of dimethyl esters is found to be 33.2 kcal/mol with a frequency factor of 1013.3 s−1.