Propellanes thermolysis

Thermolysis of compound 47 in the presence of benzophenone or naphthalene at 200-220 °C provides two products, 2,2,4,4,5,5-hexakis(2,6-diethylphenyl)pentastanna-[l,l,l]propellane, 49, and octakis(2,6-diethylphenyl)octastannacubane89, 50, as well as traces of R SnSnRj. 

There often is a correlation between the strain relief in a reaction and the rate of thermolysis, but other factors may also be of importance. The Cg propellanes 16 and 17 have quite different reactivities. Whereas 16 undergoes thermal cleavage at 360 17 undergoes cleavage at 25 °C. ° Aside from the difference in... 

The initial dimerization presumably leads to a [2.2.2]propellane derivative that undergoes thermolysis to the diene that is the observed product. The dimerization occurs in dilute solutions, but at higher concentrations, polymers are found. This finding is in accord with the proposal that these reactions occur via initial formation of a 1,4-diyl, which closes to form the cyclobutane ring. In this way, the reaction avoids an orbital symmetry disallowed pathway. The diyl could react with the alkene at higher concentrations to give a polymer. 

It is interesting that the thermolysis of cyclotristannane in the presence of benzophenone increased the yield of octastannacubane 18 to 3.6%, probably due to complexation of the intermediate R2Snl species by benzophenone". Except for the previously reported octastannacubane 18 and pentastanna[l.l.l]propellane 19, decakis(2,6-diethylphenyl)descastan-na[5]prismane 20 was also formed (Scheme 11)". The structure of the [5]prismane 20 was also established by X-ray diffraction, showing that the Sn—Sn bond lengths of 20 (av. 2.856 A) are essentially the same as those of 18 (av. 2.854 A). 

Thermolysis of [1.1.1]propellane at 114°C in a gas flow system yields methylene-cyclobutene (191), presumably by way of carbene 190 and 1,2 shift of hydrogen. At 430 °C in a second study the only product was dimethylenecyclopropane, suggested to result from a symmetry-allowed [ -f 2J rearrangement 27 similar thermal reaction of 183 at 370 °C leads to 192 and 193, which were thought to arise from secondary rearrangement of the unstable primary product analogous to 192, which is 194. Formation of 195 from 184 can be rationalized in parallel fashion by way of 196 and 197 27... 

Electrolysis of l-bromo-4-chlorobicyclo[2,2,0]hexane affords A -bicyclo[2,2,0]-hexane, which can be extracted into pentane. On standing at room temperature the olefin self-reacts to give (719), presumably by ring-opening of the initial propellane formed by [2 + 2]-type dimerization. Further developments are reported on studies of bond fixation in isomers of alkylated cyclo-octatetraenes, some of which have been prepared by the thermolysis of the appropriate propellatrienes. The... 

---