engleski

Hammet ro+ Values as Kinetic Evidence for the Concerted Biomimetic Bicylization Mechanism

Chlorides 1 (1-aryl-1-chloro-5,9-dimethyl-5,9-undecadienes) with various phenyl substituents were prepared (Y = p-OCH3, p-CH3, H, p-Br, and m-Br),and solvolysis rates were measured in 80% (v/v) aqueous ethanol and in 97%(wt/wt) aqueous 2,2,2-trifluoroethanol. The Hammett rho(+) values obtained are -1.5 and -1.8, respectively, indicating the concerted bicyclization. Comparison with rho(+) values that correspond to solvolysis of the benzylic squalene derivatives 3 (rho(+) = -1.8 and -1.6 in the same solvents) leads to the conclusion of the concerted bicyclization in 3 and may also suggest concerted bicyclization under biomimetic conditions in the natural precursor, 2,3-epoxysqualene, as well.

Extended-pi-participation. Reactivity-selectivity principle. Enzymatic cyclization. Polyene cyclizations. Solvolysis. Squalene. Biosynthesis.

nije evidentirano