Pyrolytic studies in the alicyclic series

The work describe in this thesis is concerned with the vapour-phase pyrolysis of sulphonate esters resulting in 1,3-elimination with or without rearrangement. This process is seen as going through a seven-membered transition state as in (1): the C--O and C--H bonds that cleave are coplanar while the C--C bond that migrates from the intermediate carbon is anti-periplanar to both. In order to test how rigid are the steric requirements for elimination to proceed, other systems have been pyrolysed in the course of this work. This thesis describes the pyrolysis of the two epimeric 2-noradamantyl mesylates (2) and (3) giving triaxane (4) and brendene (5), and the epimeric 10-protoadamantyl mesylates (6) and (7) giving adamantane (8) and the olefin (9). The cis-ggamma-deuterium kinetic isotope effect in the pyrolysis of 2-adamantyl esters has been investigated. This thesis describes the synthesis of (10), (11), and (12) and the analysis of the products obtained from their pyrolysis. Two methods were used for analysing the partially labelled protoadamantene (14) and dehydroadamantane (13) products obtained from the pyrolyses, namely, g. c. m. s. and 13C n. m. r. spectroscopy. The results thus obtained indicate that the pyrolyses do not go through a simple concerted mechanism as depicted in (1). The pyrolysis of (11) and (12) gave products with the same deuterium content, indicating an ion-pair intermediate causing an epimerisation of the ester function prior to or during pyrolysis. The subsequent elimination with or without rearrangement then proceed stepwise. A deuterium isotope effect is not observed for fission of the gamma-C--H bond, so that this process presumably plays no part in the rate determining step.