Question

Exploring the synthesis of [18]annulene through Glaser coupling of 1,5-hexadiyne, one encounters a trimeric intermediate. The intriguing aspect is the apparent templating toward forming a ring rather than a linear structure involving the terminal carbons. The question arises: why does this reaction favor ring formation, and is there any inherent limitation preventing the synthesis of annulenes with a different number of carbons?

a.Investigate the mechanistic details of the Glaser coupling of 1,5-hexadiyne, emphasizing the factors leading to the templating effect favoring ring formation over a linear structure. Explore whether this templating is a general trend in Glaser coupling reactions.
b.Analyze the historical development of the Glaser coupling method for annulene synthesis, focusing on the initial observations that led to the templating effect and the preference for ring formation. Evaluate whether the templating phenomenon is consistent across various alkyne precursors.
c.Examine contemporary literature on annulene synthesis and Glaser coupling, seeking recent advancements or modifications to the method. Investigate whether modern studies shed light on the templating effect and provide insights into the scope of the reaction for different ring sizes.
d.Consult experts in the field of organic synthesis and mechanistic chemistry to gain perspectives on the templating observed in the Glaser coupling of 1,5-hexadiyne. Explore the feasibility and limitations of using this approach for synthesizing annulenes with varying numbers of carbons, considering practical considerations and challenges.

Answer 1

The Glaser coupling of 1,5-hexadiyne favors ring formation over a linear structure due to templating effects, driven by factors such as stability and strain relief. The formation of a trimeric intermediate further promotes the cyclization process.

Step-by-step explanation:

The Glaser coupling of 1,5-hexadiyne in the synthesis of [18]annulene favors ring formation over a linear structure due to templating effects. This means that the reaction is guided by certain factors that promote the formation of a cyclic structure instead of a linear one.

One factor that contributes to this templating effect is the stability and strain relief associated with cyclic structures. Additionally, the intermediate trimeric species formed during the reaction further promotes the cyclization process.