PHOSPHINE ALKYLIDENES .49. 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 (1b), 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.