Stereochemistry of conjugate halogenation of 1-phenyltricyclo[4.1.0.02,7]heptane

Abstract

1-Phenyltricyclo[4.1.0.0 2,7 ]heptane reacts with N-bromo-and N-chlorosuccinimides in the presence of external nucleophiles providing products of a conjugate (electrophilic with respect to halogen) addition across the central bond C 1 C 7 of the bicyclo[3.1.1]heptane structure with a pronounces endo,anti-stereoselectivity. In similar reactions with N-iodosuccinimide the products obtained originated mainly from endo,syn-addition across the C 1 C 7 bond. The reasons for differences in the selectivity of the conjugate halogenation are discussed applying the data of the quantum-chemical calculation in the basis MP2/STO 3G of the electronic and spatial structure of the reaction intermediates, norpinanyl cations of benzyl type.1-Phenyltricyclo[4.1.0.0 2,7 ]heptane (I) was already subjected to study in ionic addition reactions initiated with an electrophilic halogen. It was shown in [1] that bromohydroxylation and bromomethoxylation of hydrocarbon I with the use of N-bromosuccinimide (NBS) occurred exclusively at the C 1 C 7 bond, and therewith the bromine cation attacked strictly the b-position with respect to the phenyl substituent from the endo-side with a pronounced anti-stereoselectivity (the ratio of endo,anti-and endo,syn-adducts was 13 : 1 and 15:1 respectively). The observed stereoselectivity was ascribed to the structural features of the intermediate norpinanyl cation of benzyl type IIa where the trimethylene fragment shielded the reaction center from the syn-side resulting in more favorable anti-attack of nucleophile. single product of endo,anti-addition [2]. However, elemental iodine added to hydrocarbon I in the endo,synstereoselective fashion (ratio of endo,anti-and endo,synadducts was 1:3). It was suggested that in the intermediate of this reaction, benzyl cation IIb, atom H 7 suffered repulsion from the bulky iodine and therefore approached the reaction site thus creating significant steric hindrancies to the nucleophile approach from the anti-side.Our recent investigations [3] demonstrated that NBS as well as N-chlorosuccinimide (NCS) in the absence of external nucleophiles in CH 2 Cl 2 solution added to tricycloheptane I across the central C 1 C 7 bond in keeping with Markownikoff rule to furnish a mixture of norpinane endo,anti-adducts corresponding to concurrent O-and N-alkylation of the succinyl moiety (ratio of the structural isomers was ~70:30 and 60:40 respectively). It was also established [3] that the chlorohydroxylation of hydrocarbon I effected by NCS in aqueous acetone occurred exclusively at the C 1 C 7 bond affording an only product of the conjugate endo,anti-addition with a norpinane structure. However the chloromethjoxylation with the use of NCS in methanol afforded a mixture of endo,anti-and endo,syn-adducts in a 49:1 ratio [4]. The numerous examples of conjugate iodination [5] as well as several instances of conjugate bromination [2, 6, 7] of unsubstituted tricyclo[4.1.0.0 2,7 ]heptane demonstrated+ ; 3K + ; + DQWL ,,D B H , , , E V\Q Later the other reactions initiated with electrophi...

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

“…The structure of compounds VIa-VIc was established from 1 H and 13 C NMR spectra. The configuration at the atom C 7 of the norpinanes under study was determined from the signals of atoms H 3 in the upfield region of the 1 H NMR spectrum, ~1.5 ppm, whereas at the opposite orientation these signals would occur in the shielding region of the syn-oriented phenyl ring and would appear at ~0.6 ppm [3,7,11]. The configuration at the atom C 6 follows from the known endo-directed electrophilic attack on the bicyclobutane system.…”

“…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].…”

“…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].…”