Phosphinalkylene, 49¹⁾ Chemie und Stereochemie des 9,10,19,20‐Tetrahydro‐tetrabenzo[a,c,g,i]cyclododecens und einiger seiner Derivate

Abstract

Twofold intermolecular C alkylation of the bis-ylide 4 with the dibromide 5 and subsequent hydrolysis yields meso-9,10,19,20-tetrahydrotetrabenzo[o,c,g,i]cyclododecene (1 b), which isomerizes on heating to give the racemate la. From l a and lb 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.Die Kondensierung starrer Einheiten an mittlere und groBe Ringe hat interessante sterische Effekte zur Folge'). Im Gegensatz zur entsprechenden Stammverbindung 23,6p8) und deren Tetradehydroderivat 3') hat 1 trotz der sich bietenden interessanten stereochemischen Aspekte bisher wenig Beachtung gefunden. 1 ist nach dem Prinzip der zweifachen intermolekularen C-Alkylierung von Bisphosphoniumyliden, das sich fur die Synthese von Benzocycloalkenen sehr bewahrt hat, leicht zuganglich geworden' -12), so dal3 Eigenschaften und Reaktionsverhalten der Diastereomeren l a und l b insbesondere im Hinblick auf sterische Effekte eingehender untersucht werden konnten.