MEMORY EFFECTS IN MULTIPLE CARBONIUM ION REARRANGEMENTS .3. EFFECTS OF BETA-METHYL SUBSTITUTION ON SELECTIVITY AND REACTIVITY IN RING EXPANSIONS OF 7-NORBORNYLCARBINYL AND 7-NORBORNENYLCARBINYL DERIVATIVES

A methyl substituent at C-7, in the β position relative to the initial site of heterolysis, causes marked changes in the products of carbonium ion reactions in the 7-norbornylcarbinyl system. Under kinetically controlled conditions of deamination in glacial acetic acid, at room temperature, almost all of the ring-expanded product from 7-methylnorbornyl-7-carbinylamine is the once-rearranged tertiary acetate, 2-methylbicyclo[2.2.2]oct-2-yl acetate, 10-OAc. Doubly rearranged product of the 1 -methvlbicyclo[3.2.1]oct-exo-2-y 1 structure, 8-OAc, is formed in acetolysis at 120° of the 7-methylnorbornyl-7-carbinyl p-bromobenzenesulfonate, but this is largely a product of thermodynamic control, resulting from the instability of the tertiary acetate under the solvolysis conditions. New syntheses of 7-methylnorborn-2-enyl-anti- and -syn-7-carbinyl derivatives (12 and 13) and of l-methyltricyclo[3.2.-1.02,7]oct-6-yl derivatives (26, 27, 32) are described. Ring expansions of the anti-7 carbinyl system might be expected to parallel those in the unmethylated series by giving products derived from 1-methyltricyclo[3.2.1.02,7]oct-6-yl cation (Lʹ), but this cation is unstable and suffers “crossover” to the 1-methylbicyclo[3.2.1]octenyl allylic cation of the Gʹ series. In the ring expansion of the syn system, the Gʹ cation expected as the major product of double rearrangement is more stable. The difference in product distributions shows that even though the once-rearranged cation is tertiary, a memory effect persists in the twice-rearranged products of deaminative ring expansion. An important side reaction in the syn system is ring closure between the double bond and the. syn-7-carbinyl side chain to produce 1-methyltricyclo[3.3.0.02,7]octan-4-yl cation, which gives rise to five new products. Two of these are identified as the corresponding acetates by independent synthesis from 1-methyltricyclo[3.3.0.02,7]octan-4-one, for which a new synthesis is reported. Ratios of acetolysis rate coefficients at 120.4° (roughly corrected for the direct displacement component) permit the evaluation of the effect of °-methyl substitution. The ratio of rates (7-methyl/ unsubstituted) is 6.3 for the syn-7-carbinyl system, 3.3 for the anti-7-carbinyl one, and 10.6 for the saturated one. The latter figure is in close (but probably fortuitous) agreement with a ratio of about 11 deduced from values in the literature for the ratio of rates of 1-methylcyclopentylcarbinyl and cyclopentylcarbinyl p-toluenesulfonates. © 1969, American Chemical Society. All rights reserved.