SUBSTITUENT EFFECTS AND HOMOBENZYLIC CONJUGATION IN BENZONORBORNEN-2 (EXO)-YL P-BROMOBENZENESULFONATE SOLVOLYSES

A series of aromatic-substituted benzonorbornen-2(exo)-yl p-bromobenzenesulfonates was prepared and the solvolysis reactions were studied. The relative rates of acetolysis of 6-CH3O, H, 7-CH3O, 7-CH3O-6-NO2, and 6,7-(NO)2 derivatives at 77.60° were 178, 1, 0.72, 1.1 X 10−3, and 1.1 X 10−5, respectively. The solvolyses of 6-CH3O, H, and 7-CH3O derivatives (1e, 2e, and 3e) proceed with retention of configuration yielding only the exo-substituted products (the corresponding benzonorbornen-2(exo)-ols or their esters). However, the strongly deactivated 7-CH3O-6-NO2 and 6,7-(NO2)2 derivatives (4e and 5e), besides the products with retention, give the inverted endo products and the olefins. The analysis of the data indicates major participation by the aromatic ring, facilitating solvolysis and causing exo substitution in the product. When an optically active material (8e-OBs, the parent system) is used, the participation brings about a racemic product. When the optically active 6,7-dinitrobenzo-norbornen-2(exo)-yl brosylate(6e-OBs) was acetolyzed, the produced exo acetate retained 4.51% of the original optical purity and the endo acetate retained 25.7%. By these data and the results of the acetolysis of labeled 6,7-dinitro-3(exo)-deuteriobenzonorbornen-2(exo)-yl brosylate (7e-OBs), it was proven that the dinitrobenzene ring is migrating. Also it was shown that the endo product from 5e-OBs is partially the result of an Sn2 reaction of the original brosylate and partially the result of the same reaction with the brosylate formed by internal return of an ion pair. Both the observed rates and the anchimerically assisted parts of the observed rates are correlated with good precision by using the modified Hammett relationship, log (k/k0) = pó+, yielding identical straight lines with p =– 3.26. © 1969, American Chemical Society. All rights reserved.