The Chemistry of the trans-Trimethylenenorbornene Ring System. 3. Effects of a trans-5,6-Trimethylene Bridge on the Norbornyl Cation

Article abstract of DOI:10.1021/jo00193a004

Hydration of the epimeric mixture 9-carboxy-trans-5,6-trimethylene-2-norbornene (1) in dilute aqueous acid afforded the 9-carboxy-endo,cis-5,6-trimethylene-5-norborneols (2a) as sole product.Initial protonation of 1 was shown to be regiospecific.The rearrangement to 2a was found to occur solely by way of a 6,2-type hydride shift, while Wagner-Meerwein rearrangement and 3,2-type hydride shift were completely suppressed in the intermediate cation.It was concluded that the high degree of strain associated with the trans-trimethylene bridge in 1 was responsible for the unusual behavior of the intermediate.