STERICALLY CROWDED CYCLOHEXANES .10. SYNTHESIS, CONFORMATION AND DYNAMICS OF -TETRAMETHYLTETRASPIRO[2.0.3.1.3.1.3.0]HEPTADECANE

The synthesis, conformation and dynamics of tetramethyltetraspiro[2.0. 3.1.3.1.-3.0]hepradecane (11) are described. 11 adopts a chair conform ation in solution. Its barrier of inversion proved inaccessible by DNM R but could be determined from equilibration studies with stereoselect ively labeled [1-C-13](e)-11. The results were as follows: Delta H-not equal = 104.7 kJ/mol Delta S-not equal = -13.1 J/mol.K and Delta G(29 8)(not equal) = 108.6 kJ/mol. The stereoisomers of [1-C-13](e,a)-11 th us represent a further case of conformational isomerism within the cyc lohexane family. (C) 1997 Elsevier Science Ltd.