Synthesis and reactivity of some Bicyclic and Tricyclic Medium Ring Systems

Abstract

In connection with a broader interest in transannular hydride shifts and bridgehead reactivity in bridged bicyclic and tricyclic systems, a synthetic route to hitherto unavailable 3,7 disubstituted bicyclo(3,3,2) decai.es is described. Bridging of the readily available Meerwein ester to its corresponding double homologue was followed by regio-specific decarboxylation to achieve unprecedented 1,8 distbstitution in the homo-adamantane skeleton. Subsequent degradative stages afforded 7-exo methylene bicyclo(3,3,2)decan-3-one. X-ray crystallographic structural ^ 8 elucidation of an intermediate, 1,8- icarbomethoxy-tricyclo(4,3,1, T ’ )undecane, confirmed the complete regio-specificity of the decarboxylation and showed that the preferred ground state conformation of the compound has an almost C2 symmetry with its ethano bridge virtually eclipsed (dihedral angle 2 ). Exo-7-hydroxy- icyclo(3,3,l)nonan-3-one was synthesised by ozonolysis of 7-exo-methylene bicyclo(3,3,1 )nonan-exo-3 ol. The ketol undergoes a degenerate base catalysed rearrangement via a specific 1,5 transannular hydride shift. The presence of epoxide by-products from the ozonolysis is rationalised on steri.c grounds. Attempts to prepare specifically 1C0 labelled, and optically active, i-ne.h>,. bicyclo(3,3,l)nonan-3,7-dione by ozonolysis of the corresponding labelled (*®0, 757.) exo-methylene ketone resulted in almost complete label loss. 1'|lj observation is discussed in terms of recent mechanistic theory relating to ozonolysis of olefins. Similar results from ruthenium tetroxi.de oxidative cleavage are also discussed kirvrlo(3. 3,1 )nonanc has been svnt b i.s< i rh* i i^-trime thy 1 ammonium iodide of 1,3 diamln and preliminary attempt* made to identify the product im .-d dr.rlu the pyrolysis of its di-hydroxide.