Sterisch gehinderte Doppelbindungssysteme, 2. Über die Darstellung hochsubstituierter 1,3‐Diene

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Abstract
Sterically Hindered Double Bond Systems, 2. — On the Preparation of Highly Substituted 1,3‐DienesHighly alkylated 1,3‐dienes may be prepared by treatment of 2‐butyne‐1,4‐diol derivatives with organocuprates in good yield. Thus, the 2,3‐dialkylated butadienes 6a—d are obtained by treating the diacetate 4 with two equivalents of the cuprates prepared from the Grignard reagents 5a—d with CuBr/LiBr. Analogously, meso‐14 is converted into a mixture of the di‐tert‐butyl‐2,4‐hexadienes (Z,E)‐ and (Z,Z)‐15. The procedure may be extended to the synthesis of unsymmetrically substituted 1,3‐dienes by either treating the appropriate diacetates with two equivalents of the same cuprate as examplified by the conversion of 18 into 19a and 19b or by employing a stepwise approach in which only one reactive acetate leaving group is available for the cuprate reagent at any given time, thus allowing the change of the organometallic reagent in the course of the synthesis (preparation of the dienes 26 from the monoacetates 22). The mechanisms of these reactions as well as those of several reactions leading to sideproducts are discussed.

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