Butadiyne Moieties as Spacers and Framework

3-butadiyne units in 29 and 33-35 act as rigid framework which spans a cavity for guests (see below). This function of a polyalkyne unit was also used to construct cavities with receptor properties. Among monocydic receptors were 36 and 37 with two and three n units and two and three butadiyne spacers [41, 42]. Both were constructed by Eglinton coupling. Other cyclic systems which form intracavity complexes are the cyclophanes 38 and 39 [43, 44] (Chart 7.1). 

The latter system is soluble in water and acts as an acetyl acceptor. Water-soluble properties are also reported for the tetramer 40 obtained by homocoupling of a 1,4-cis-ethynyl substituted glucopyranose [45] (Chart 7.2). The tetramer 40 contains five water molecules in the crystal [45]. 

Rigid macrocycles with two, three and four butadiyne units (40-43) [45-47] are listed in Chart 7.2. All three isomers of the [8.8]cydophane 41 ortho, meta and para) [46] have been stmcturally characterized, but the hollow core proved to be too small for the inclusion of guest molecules. In the case of 42 the cubane units 

Chart 7.1. Examples of cyclophanes with butadiyne units. 

Chart 7.2. Rigid macrocycles 40-43 with two, three and four butadiyne units. 

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