Molecular Asymmetry in trans-Thiacycloalkenes. 2. Barriers to Interconversion of Diastereomeric Conformers of 2-Substituted Nine- to Eleven-Membered (E)-Thiacycloalk-4-enes

Article abstract of DOI:10.1021/jo01306a014

trans-Thiacycloalk-4-enes of ring size 9 to 11 carrying a substituent (CH3 or COOCH3) at C₂ were synthetized.These species have two elements of chirality (a plane and a center) and exist as diastereomeric pairs which may interconvert via a conformational process (180 deg revolution of the ? plane inside out the ring).The energy barrier for this process has been measured by dynamic 13C NMR and found to be 16.4, 10.7, and 8.3 (or 7.0) kcal/mol for the 9-, 10-, and 11-membered-ring compound, respectively, lower than those for their carbocyclic analogues.The lower barriers may arise from the heteroatom across the ring, which, unlike the corresponding carbon in the homocyclic counterpart, carries no ligand and allows for less steric compression in the transition state.