Phosphinalkylene, 49 1) Chemie und Stereochemie des 9,10,19,20‐Tetrahydro‐tetrabenzo[ a,c,g,i ]cyclododecens und einiger seiner Derivate

Phosphine Alkylidenes, 49 1) . – Chemistry and Stereochemistry of 9,10,19,20‐Tetrahydrotetrabenzo[ a,c,g,i ]cyclododecene and of Some Derivatives Twofold intermolecular C alkylation of the bis‐ylide 4 with the dibromide 5 and subsequent hydrolysis yields meso‐9,10,19,20‐tetrahydrotetrabenzo[ a,c,g,i ]cyclododecene ( 1 b ), which isomerizes on heating to give the racemate 1a . From 1a and 1b the isomeric dibromides 7 – 10 are synthesized. Reaction of 7 – 10 with phenyllithium leads to the formation of the polycyclic compounds 11, 12, 13 , from which 12 may be dehydrogenated to the unsaturated compound 14 . Reaction of the dibromides 7 – 10 with silver acetate occurs with retention yielding the acetates 15 – 18 , which may be hydrolysed to the corresponding alcohols. With the knowledge of the structures of compounds 15 – 22 the stereochemistry of the synthesis and the Wittig ether rearrangement of the diethers 24 can be elucidated. In the reaction of the dibromides 7 – 10 with sodium acetate elimination takes place instead of substitution. Starting from 7 and 8 the polycyclic hydrocarbon 31 is formed via the carbenium ion intermediate 26 and subsequent transannular reaction. 31 is dehydrogenated to yield 32 , whose X‐ray structural analysis shows a multi helical structure. Reaction of the base potassium tert ‐butylate with the dibromides 7 – 10 leads to the formation of isomers of the diolefin 2 .