Cyclic unsaturated compounds. XXXV. Intramolecular thermal 1.5-shift of hydrogen in cyclohepta-1,3-diene series.

INDO calculations on the sigmatropic [1, 5] H-Shift in 1,3-cyclohexadiene and 1,3,5-cycloheptatriene A homo-cyclopentadienyl transition state model

“…In Table 2 we compare the theoretical and the experimental activation enthalpies. The experimental value for cyclohexadiene, reported in this study, was obtained starting from 1,3-1D,4D-cyclohexadiene, using NMR-monitoring [4] 29 [5] 29 [6] 32 37 [7] 27 of the reaction mixtures. Reaction temperatures ranged from 303°C to 330 ° C. More experimental details will be published elsewhere [11].…”

Thermal [1,j] sigmatropic rearrangements

“…Roth35® established that thermal hydrogen migration in 1,3-cyclopentadiene and indene was indeed a concerted [1,5] process by substituting deuterium for hydrogen in appropriate positions, and following the migration process by NMR techniques. For example, indene (50) undergoes the following equilibrium proceeding through the isoindene intermediate S1.35b Almy and Cram36 established that migration in the indene system is a suprafacial, stereospecific process, and also showed a definite isotope effect that favored H migration over D migration. Alkyl substitution at C-5 (see Scheme III) lowers the activation enthalpy for migration of a C-5 H in cyclopentadiene,37,38 while [1,5] H migration from C-5 in 5-[5-cyclopentadienyl]-1,3-cyclopentadiene occurs with particular ease.39 [1,5] migration in the 1,3,5-cycloheptatriene system has been extensively studied.…”

1,5‐hydrogen shifts in methyl‐1,3‐cycloheptadienes

“…He 13 subsequently reported the thermal interconversion of the four isomeric methyl‐1,3‐cycloheptadienes, which also presumably occurred by 1,5‐hydrogen shifts. While theoretical studies on the 1,5‐hydrogen shift in 1,3‐cyclopentadienes have been reported [5, 7], there appear to be no reports of ab initio calculations on hydrogen shifts in the larger cycloalkadienes 14.…”