1‐Substituierte Cycloheptatrienverbindungen

Cycloheptatriene reacts with acrylic esters, in the presence of catalytic amounts of tricarbonyl‐triphenylphosphine‐nickel, to yield a mixture of α‐cycloheptatrienyl‐propionic acid esters ( 2a ) substituted in various positions. Methacrylic acid ester yields likewise α‐cycloheptatrienyl‐isobutyric acid ester ( 3a ). Both types of ester mixtures undergo thermal isomerizations by 1,5‐hydrogen shifts to give mixtures which contain predominantly the (C‐1)‐substituted cycloheptatrienyl‐carboxylic acid esters ( 2a , 3a ). Pure α‐(1‐cycloheptatrienyl) derivatives can be prepared from 2a and 3a . A detailed NMR. study of the ester mixtures before and after thermal isomerization shows the proportions of the various isomers in the mixture. The mechanism of the formation of 2a and 3a is explained in terms of a catalysed ene‐reaction of the primary formed 7‐substituted cycloheptatriene derivatives with subsequent consecutive 1,5‐hydrogen shifts.