Electrophilic cleavage of cyclopropanes. III. The reaction of molecular bromine with tetracyclo[3.2.0.0^2,7.0^4,6]heptane^1,2

Abstract

. The ionic addition of molecular bromine to tetracycl0[3.2.0.O'~~.O~~~]heptane (quadricyclene) has been investigated in a variety of solvent systems. Depending upon the nature of the solvent, three or more of six dibromo and five solvent-incorporated adducts are isolable. A mechanism involving a series of ion-pairs and competitive edge-on vs. corner (end-on) attack is proposed. DENNIS G. GARRATI. Can. J. Chem. 58, 1327 (1980). On a etudie I'addition ionique du brome moleculaire sur le tetra~~cl0[3.2.0.0z7.0".~]heptane (quadricyclkne) dans plusieurs systemes de solvants. Dependant de la nature du solvant, on a pu isoler un minimum de 3 de 6 adduits dibromks et de 5 adduits lncorporant le solvant. On propose un mecanisme impliquant une sene de paires d'ions et des attaques competitives par le c6tC ou par le sommet (end-on).[ terms of an exo bromine atom, 3a (2,4). Br COOH COOHThe results, while indicative of apparently 3a 36stereospecific inversion of configuration at carbon during both electrophilic cleavage and subsequent nucleophilic attack, contrast with other reports (5) of more varied stereochemical pathways. For example, Skell and co-workers (6) have reported the ionic bromination of dehydroadamantane, 4, in the presence of isoamyl nitrite to give a 59:41 mixture of the isomeric 2,6-dibromoadamantanes, 5 and 6. They argued that since all aspects of ionic brominations of cyclopropanes point to formation of a 1-bromo-3-carbonium ion, it is reasonable to attribute to the second step, the reaction with bromide ion, the proportioning between axial and equatorial approach. An alternative rationalization of their data, however, would be a competitive attack by bromine, both from the edge and the corner, followed by stereospecific attack by bromide ion with inversion of configuration at carbon.In their detailed mechanism, Skell and co-

Synthetic Chemistry of Quadricyclane

“…In general, the data reported in both papers [1,158] are in a good agreement. Bromination of Q results in dibromides 288-290a, however formation of minor byproducts -dibromide 291 was observed in cyclohexane, and dibromide 293 in a mixture of methanol/methylene chloride.…”

“…Bromination of Q results in dibromides 288-290a, however formation of minor byproducts -dibromide 291 was observed in cyclohexane, and dibromide 293 in a mixture of methanol/methylene chloride. When bromination is carried out in alcohols, the formation of substantial amount of products 294 and 295 is detected [158].…”

“…The formation of variety of products in the reaction of Q with bromine was explained as being a result of two competitive processes [158] -attack of electrophile on cyclopropane ring edge (C-C bond of cyclopropane ring, "edge-on") or at the corner carbon ("end-on"), resulting in the formation of two different cations 296 and 297 respectively. The stereochemical outcome of the reaction is defined by further transformation of these two intermediates.…”

New systems for classical nitrosohalogenation of alkenes 1. Reactions of alkenes with ethyl nitrite in the presence of phosphorus halides and thionyl chloride

“…How ever, we failed to purify the dimer of endo 6 trifluoro methyl cis exo 2 chloro 3 nitrosobicyclo[2.2.1]heptane (20), which remained in the mother liquor, from an im purity of compound 18 by recrystallization. The struc tures of these compounds were established based on the analysis of the chemical shifts in the 1 H NMR spectrum.…”