Approaches to Terminal Diacetylenes, Precursors to New Substituted Polyacetylenes

A number of synthetic routes to substituted 1,6‐heptadiynes, specifically 3,3,5,5‐tetramethyl‐1,6‐heptadiyne (5), cis‐1,3‐dimethyl‐1,3‐diethynylcyclopentane (3, R=CH3) and cis‐1,3‐diethynylcyclopentane (3, R=H), have been examined. These diacetylenes are precursors to new substituted polyacetylenes via cyclopolymerisation. Two major synthetic difficulties were encountered: (1) low reactivity of neopentyl systems to nucleophilic displacement in the cases of 3, R=CH3 and 5, and, conversely, (2) lability of isoalkyl type structures such as the intermediates for 3, R=H toward elimination during nucleophilic displacement reactions. These fundamental problems were compounded by the fact that all the intermediates are difunctional, giving rise to the statistical problem of mixed functionalities. While none of the desired diacetylenes was prepared in a pure state, a number of new intermediate compounds were synthesised. Furthermore, an impure sample of 3, R=H did yield a polymer film in preliminary experiments.