Valenzisomerisierung von Cyclodeca‐1,5‐dien. Cyclodecapolyene, 2. Mitteilung

The products isolated from the H OFMANN degradation of trans and cis 1,6‐bis‐trimethylammonio‐cyclodecane (1a) depend on the reaction temperature. When carried out below 100° or when W ITTIG'S low‐temperature modification, i.e. with KNH 2 in liquid ammonia, is employed, cyclodeca‐l,5‐ and ‐1,6‐dienes are formed almost exclusively, as shown by their hydrogenation to cyclodecane. When heated above 70° cyclodeca‐l,5‐diene (2) undergoes valency isomerisation to 1,2‐divinylcyclohexane (4). This compound is obtained directly in ca. 45% yield besides 46% of non‐isomerisable cyclodeca‐l,5‐ and ‐1,6‐dienes when the H OFMANN elimination is carried out at 120–150°. In addition, ca. 9% of octalines are formed by a transannular elimination reaction. The C OPE elimination reaction of the bis‐N‐oxide of trans and cis 1,6‐bis‐dimethylarnino‐cyclodecane (1c) at 120–150° affords a similar mixture of products containing ca. 43% of 1,2‐divinylcyclohexane. The ease with which cyclodeca‐l,5‐diene undergoes valency isomerisation is attributed to the concomitant relief of strain and to the proximity of carbon atoms 1 and 6 in the trans / trans isomer.