STERICALLY CROWDED CYCLOHEXANES .9. SYNTHESIS, CONFORMATION AND DYNAMICS OF HEXASPIRO[2.0.4.0.2.0.4.0.2.0.4.0]TETRACOSANE

The synthesis, conformation and dynamics of hexaspiro[2.0.4.0.2.0.4.0. 2.0.4.O]tetracosane (3) are described. At room temperature in solution , 3 exists as 4:1 mixture of a rapidly interconverting twistboat confo rmation and a fixed chair conformation. Tile activation parameters for the chair-to-chair interconversion followed from a bandshape analysis of exchange broadened C-13 NMR spectra of [1,10,18-C-13]-3 as Delta H -# = 57.1 kJ/mol, Delta S-# = 35.4 J/mol.K, and Delta G(298)(#) = 67.6 kJ/mol. 3 is only tile second case where a per(cyclo)alkylated cycloh exane populates a chair and a twistboat, and the first case where the twistboat predominates. (C) 1997 Elsevier Science Ltd.