- CYCLOADDITION OF SUBSTITUTED CYCLOPROPYL ETHERS TO TETRACYANOETHENE
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The cyclopropyl methyl ethers 2-4, 14 and 15 and tetracyanoethene (TCNE) give, in a multistep cycloaddition, the 1,1,2,2,-cyclopentanetetracarbonitriles 5-8, 16 and 17.It has been estabilished that the cycloaddition reactions take place with inversion of configuration of the cyclopropyl C2 (or C3) carbon atom and racemization at the C1 carbon atom.In the presence of methanol, the all-cis-2,3-dimethylcyclopropyl methyl ether 3 and TCNE give, in a slow reaction, a mixture of cycloadducts 7 and 8, together with the ring-opened tetracyanopentanone acetal 13, whereas the phenyl-substituted cyclopropyl ethers 14 and 15 yield exclusively, and relatively rapidly, the corresponding acetal 19.These results strongly indicate that the reaction proceeds via zwitter-ions which are formed by SH-2-type attack of TCNE anion radicals on the cyclopropane ring.
- Wiering, P. G.,Steinberg, H.
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