IMPACT OF HIGH-LYING SIGMA ORBITALS AND EXTENSIVE THROUGH-BOND INTERACTION ON CHEMICAL REACTIVITY .2. SOLVOLYTIC STUDIES OF HYPOSTROPHENE DERIVATIVES

Acetolysis of exo- and endo-tetracyclo[5.3.0.02,6.03,10]decan-4-yl tosylates (6b and 8b) in buffered HOAc at 71 °C produced 16b (together with 2% of 6c in the endo case), but at rates estimated to differ by a factor of 170 (with 6b faster). Comparable solvolysis of the unsaturated exo tosylate 3b (at 25.9 °C) led rapidly to 18b (50%), 19a (5%) and 19b (45%), a product distribution quite unlike that obtained from its endo epimer 5b (18b accompanied by some polymer formation). These findings demonstrate that the frequently observed ability of a proximate double bond to engage in transannular participation has been overridden by lateral σ-bond participation. The kinetic and product data suggest that the first cation emanating from 5b is classical, while that from 3b is generated with anchimeric assistance and characterized by σ delecalization. Whereas acetolysis (71 °C) of exo-cyclopropyl derivative 10b returned only 20a, its endo counterpart 15b gave a complex acetate product mixture at a rate approximately 440 times slower. The involvement of neighboring-group participation could again be implicated for 10b, since interaction of the cationic center with the cyclopropane ring is effectively repressed. The rate constants and product distributions provide convincing demonstration of the effectiveness with which such anchimeric assistance can accelerate and control the ultimate outcome of cationic rearrangements. © 1978, American Chemical Society. All rights reserved.