Tricyclo heptanes, structure

All natural T. m. have the tricyclo[2.2.1.0 ]heptane structure, the parent C,o-skeleton is called tricyclene. Although the ring system is strained it seems to be... 

Methyl tricyclo[4.1.0.0 ]heptane-l-carboxylate gives a cation-radical in which the spin density is almost completely localized on C-1 while the positive charge is on C-7. The revealed structural feature of the intermediate cation-radical fairly explains the regioselectivity of N,N-dichlorobenzenesulfonamide addition to the molecular precursor of this cation-radical. In the reaction mentioned, the nucleophilic nitrogen atom of the reactant adds to electrophilic C-7, and the chlorine radical attacks C-1 whose spin population is maximal (Zverev and Vasin 1998, 2000). 

The versatility of the addition reaction of organocuprates to activated cyclopropanes and the stereospecificity have made this reaction an important step in the synthesis of a variety of natural products such as prostaglandins and sesquiterpenes.One of the advantages of this reaction lies in the possibility of introducing complete side chains into certain structures. An example is the reaction of 3-e Jo-substituted tricyclo[3.2.0.0 ]heptan-6-ones 17 with the lithium cuprate that contains a side chain with a protected functional group. The substituted bicyclo[2.2.1]heptan-2-ones 18 were obtained in high yields. 

Various bi- and polycyclic hydrocarbons containing bicyclo[3.1.0]hexane, spiro[2.4]heptane, or other structural units encompassing a three-membered ring, can produce six-membered ring compounds on thermal decomposition. Most thermolyses of this type have been carried out in the gas phase at low pressures, and kinetic parameters have been measured for many of these decompositions. Yields of the major products, even when not specifically noted, were usually high, but additional minor products were frequently detected (Table 1). Most thermochemical rearrangements of cyclopropane containing hydrocarbons proceeded via diradical intermediates, but concerted mechanisms were invoked in a few instances such as that of anti-tricyclo[3.1.0.0 " ]hexane. 

Let us describe some frequently encountered polycyclic structures. Bicyclo[2.2.1] heptane, also known as norbomane, is the basic structure of a series of natural products. The tricyclic compound adamantane (tricyclo[3.3.1.L ]decane) is in principle the smallest structural fragment of diamond and its structure appears on the list of pharmaceutically important products. Adamantane was synthesized for the first time in 1941 at the University of Zagreb by Vladimir Prelog. 

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