Reduktive Umwandlungen, 18⁽²⁾ Cycloanellierung und Überbrückung von Cyclooctatetraen⁽¹⁾

Abstract

Reductive Transformations, 18[2]. – Cycloannulation and Bridging of Cyclooctatetraene[1] Reductive alkylations of cyclooctatetraene (1) with biselectrophiles have hitherto been described as proceeding solely under 1,2‐cycloannulation. Using different alkylating agents with varying chain lengths, conformational mobility, and leaving groups we succeeded in achieving regio‐ and stereoselective reactions of the intermediate monoalkyl monoanion 3. By systematic variation of the biselectrophiles the subtle competition of 1,2‐ versus 1,4‐ and of 1,n‐cis‐ versus 1,n‐trans‐cyclization is elucidated. It is shown that the regio‐ and stereoselectivity are controlled mainly by the structure of the alkylating reagents while other parameters such as solvent or leaving group do not play an important role. Reductive alkylation of 1 provides an easy access to a large number of compounds which may be oxidized to new cyclooctatetraene systems or serve as substrates for further skeletal rearrangements. – X‐ ray structure analyses are performed for compounds 15, 27 a, 28, and 29.