Cyclopropane ring tricyclo octane

Attempts to observe circumambulatory rearrangement in the 2,6-unri-tricyclo [5.1.0.03,5]octane-2,6-diyl dication 178 have been unsuccessful.397 The dication 178 would appear to rearrange instantaneously to the homotropylium ion 179 by proton elimination. However, substituted dications of type 178 (e.g., 180) are quite stable they are static, and a substantial part of the charge is delocalized into the cyclopropane rings. 

In the second, aprotic decomposition of tosylhydrazone 101 was shown to proceed with conventional cyclopropane ring formation.148 On catalytic hydrogenation, one of the two products (102) was converted to tricyclo[3.3.0.03, 7]-octane (103) (Scheme 20). This hydrocarbon is not only a dehydrobicyclo[3.3.01-octane but is also of interest because of its bisnor relationship to adamantane. 

Some tri- and tetracyclic alkanes contain two cyclopropane moieties locked into a fixed orientation. These arrangements might give rise to interesting stereoelectronic effects in the interaction between the cyclopropane rings. For example, CIDNP effects during electron-transfer reactions of syn- and a/jn -tricyclo[5.1.0.0 ]octane syn-, anfi-89) indicate significantly different structures for their radical cations. 

As an alternative to a radical chain mechanism for this bromination, a cationic mechanism has been proposed for the reaction between 48 and A-bromosuccinimide. It involves attack of bromine at C6 of 48 leading ultimately to the cyclopropylmethyl cation A. This cation is a bromo derivative of tricyclic cyclopropylmethyl cation, which has been shown to be the common intermediate in the solvolysis of esters of tricyclo[3.2.1.0 ]octan-3-ol, endo- and exo-tricyclo[3.2.1.0 ]octan-4-ol and of cxo-bicyclo[3.2.1]oct-2-en-7-ol. It has been shown that under long-lived ion conditions at — 78 C such cations are the most stable species that are formed from bicyclo[3.2.1]oct-2-en-3-ol and from bicyclo[3.2.1]octa-2,6-dienes. In kinetically controlled reactions, which are postulated to proceed via cyclopropylmethyl cations a tendency can be seen towards formation of products retaining the cyclopropane ring. This case is achieved through loss of one of the protons at C4 of A. 

Stereoselective cleavage of internal cyclopropane rings in tricyclic and tetracyclic structures is often cleanly accomplished by means of the lithium/ammonia reduction. For example, tricyclo[3.3.0.0 ]octan-3-one (19) was reduced to ds-bicyclo[3.3.0]octan-3-one (20) in 65% yield. 

The stereochemistry of the ring-opening reaction of exo- and e (7o-tricyclo[3.2.1.0 " ]octane 41 by proton, deuterium and mercury(II) ions has been investigated. When the e t/o-isomer was treated with methanol in the presence of a catalytic amount of p-toluenesulfonic acid, endo-2-methoxybicyclo[3.2.1]octane (42a) was obtained in high yield. The exo-compound reacted in an analogous fashion to give exo-2-methoxybicyclo[3.2.1]octane (44a) as the major product and exo-2-methoxy- yn-7-methylbicyclo[2.2.1]heptane (45 a) which resulted from the cleavage of an outside cyclopropane bond. 

The cleavage with hydrogen bromide has been applied to the ring opening of a number of cyclopropanes incorporated into a polycyclic system. Treatment of tricyclo[3.3.0.0 ]octan-3-one (36) with hydrogen bromide in dichloromethane gave two bromo-substituted bicycles 37 and 38 as the result of the cleavage of the two different activated cyclopropane bonds. ... 

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