Regio- and stereoselectivity in halomethoxylation of 7-phenyl-1-phenylsulfonyltricyclo[4.1.0.02,7]heptane

Abstract

The reaction of 7-phenyl-1-phenylsulfonyltricyclo[4.1.0.0 2,7 ]heptane with N-halo (chloro, bromo, iodo)succinimide in methanol led to the formation of a single product of conjugate syn-addition to the central C 1 -C 7 bond of the norpinane structure with a halogen atom in the geminal position to the sulfonyl substituent. The stereochemical result of the addition originates from the features of the reaction intermediate structure, a norpinanyl cation of a benzyl type where the reaction site is shielded from the nucleophile attack from the anti-direction by the sulfonyl group whose oxygen atom is approached to the reaction site to a distance of ~1.45 according to the nonempirical calculations by the 6-31G method; this distance is nearly by half less than the sum of van der Waals radii of C···O.It was established experimentally that 1-phenyltricyclo[4.1.0.0 2,7 ]heptane (I) and its 7-X-substituted derivatives II-V were involved into the electrophilic addition: hydromethoxylation[1, 2], hydration [2, 3], ionic hydrogenation [4], methoxymercuration [1], halogenation [3], halomethoxylation [1, 3, 5, 6], haloamination [6], and other reactions of conjugate halogenation [3,7] and exhibited strict chemo-and regioselectivity. In these reactions the C 1 -C 7 bond opened at an electrophilic attack on the position 7, as a result of the benzyl stabilization of intermediate norpinanyl cation A [8,9]. From this rule in this series only the hydration and the hydromethoxylation of tricycloheptane I are excluded, where the chemoselectivity of the addition is broken: alongside the norpinane adduct (4 and 18% respectively) formed predominantly a norcarane adduct (54 and 56%) corresponding to the opening of the C 2 -C 7 bond also at the electrophilic attack on the position 7 [2]. As to the stereochemistry of the addition to the C 1 -C 7 bond, here its certain dependence is observed on the nature of the reagent and the character of the substituent X in the position 7. Yet this dependence corresponds only to the stage of the transfer of the nucleophilic coreagent to carbocation A, since the stage of the electrophilic attack on the central bicyclobutane bond C 1 -C 7 is considered to be strictly endo-directed [8,9]. As a result the X = H (I), CO 2 Me (II), SO 2 Ph (III), Br (IV), Cl (V); E = H, Cl, Br, I, HgOAc; Nu = H, OH, OMe, OCOR, Cl, Br, I, NHCN, SCN, N(COCH 2 ) 2 X Ph X E Ph Nu X E Ph Nu anti-adduct Nu + E + syn-adduct I _ V A X E Ph _