1. 3-butadiyne unit

The oxidative coupling, however, normally provides better results, as was demonstrated by the reasonably efficient cyclization of 179 to the homoconjugated 16-membered macrocycle 180 (14% yield) with alternating ethyne and butadiyne units (Scheme 34) the alternative Cadiot-Chodkiewicz coupling of the bisterminal diyne 38 and the dibromotriyne 177 gave only a 2.6% yield of 180 [4]. 

A third route to higher or expanded radialenes (see Introduction) also rests on an insertion principle . It employs the rodlike butadiyne unit and inserts it between the neighboring double bonds of the basic radialene systems 181, thus converting these into the boxlike molecules 12 (equation 26)107,108. 

Using 1,4-dilithiobutadiyne and /-Pr2ClSiSiCl/-Pr2, Matsumoto et al. have prepared ryc/ >-[(disilanylene)(buta-diyne)]s 272-274 that contain 12-, 18-, and 24-membered rings, and consist of alternating sequences of disilane and butadiyne units (Scheme 39).362... 

The 11-membered and larger ring systems. Twenty- and 22-membered cyclic bis(l,3-butadiynes) 30 and 31 with selenium centers placed in the a-position to the 1,3-butadiyne units were synthesized and determined by X-ray analysis <2004JOC2945>. X-Ray crystallographic structure was obtained for 32, which showed a cavity size estimated to be 7.8 x 7.4 A2. The diagonal Se-Se distances are 10.1 and 937 A, respectively <2005MI191>. 

Hydrazine hydrate reacts with 1,3-butadiyne moieties in competition with the carbonyl groups. Therefore, tosylhydrazine is employed for the selective reaction with the latter. The sodium salts of the resulting tosylhydrazones are heated to give the diazo compounds 16,18, and 20 [8, 10]. As some of the 1,3-butadiyne derivatives in Table 11-2 undergo spontaneous polymerization in the solid state (see Section 11.4.1), they have to be kept in solution. 1,3-butadiyne units are also known to react with diazo groups [11] and therefore the diazo compounds such as 16, 18, and 20 must be kept refrigerated. 

Haley et al. synthesized thiophene analogues 4.38-4.40 of didehydrotribenzo [18]annulene by Eglinton cyclooligomerization in order to study their optical properties in comparison with the basic [18]annulene system (Chart 1.54). The Cs-symmetric 4.38 involving 2,3-thienylenes connected by butadiyne units can be regarded as the next higher expanded macrocycle in the series benzo[l,2-fc 3,4-b 5, 6-fc ]trithiophene 4.4 and trithienocyclotriyne (TTC) 4.34 [413]. 

The terminal -C=C-C=C-H containing platinum monomer can be condensed with fran5-Pt(PnBu3)Cl2 to afford the linear rod-like polymer where the platinum metal alternates with the butadiyne unit. The presence of the... 

Another type of stimulus-responsive supramolecular polymer was produced using the complementary affinity of a bisporphyrin (Figure 7.20). The bispor-phyrin units were connected with 1,3-butadiyne units to produce homoditopic tet-rakisporphyrin 23. The iterative self-assanbly of 23 gave rise to supramolecular nanometric polymeric assemblies. An electron-deficient aromatic guest can aggressively bind within the bisporphyrin cleft, causing the supramolecular polymeric assemblies to dissociate. 

Carbon-rich Cycles with Two and More 1,3-Butadiyne Units - Syntheses, Structures and Reactivities... 

In view of this very broad development of alkyne chemistry we have had to limit our review in this chapter and have focused mainly on our own recent work which was concerned with ring systems containing 1,3-butadiyne units. We do not intend to discuss here the many [4n+2]7i- and [4n] t-dehydroarmulenes containing 1,3-butadiyne units [8], the [Njpericydynes [9], or shape-persistent macrocycles consisting of phenyl rings connected with alkyne units [10, 11]. 

Our interest in the topic of this chapter was stimulated by earlier spectroscopic investigations [12] on cyclic diynes with two parallel triple bonds in close proximity and transannular reactions between the triple bonds [13, 14]. We were further inspired by the results of Wegner [15] who found out that parallel aligned 1,3-butadiyne units (Scheme 7.1) yielded, upon irradiation or heating, a 1,4-addition in a topochemical reaction [15, 16]. 

The above mentioned coupling procedures were also used to prepare a large variety of nonconjugated and conjugated systems with 1,3-butadiyne units as building blocks that are summarized in various reviews [1, 2, 28, 29]. 

Herein we mention that Pd-catalyzed coupling reactions between alkynes are also available to generate symmetrical 1,3-butadiyne units [21b, 22]. So far they have not been applied to the preparation of cyclic systems with 1,3-butadiyne units. 

Bauerle et al. have recently published a noncatalytic procedure allowing the isolation of a bis-platinum macrocycle which was transferred to a conjugated system with two 1,3-butadiyne units by a reductive elimination process [34]. This technique was used to prepare cyclotetracosa-l,3-ll,13-tetrayne (15) (Scheme 7.4) [35]. The reaction of dichloro-l,3-bis(diphenylphosphinopropane)platinum(ii) (12) with 1,11-dodecadiyne yielded 13(11). This species was reacted again with 12 to afford the cyclic system 14(11) which was oxidized with iodine to obtain cyclotetrayne 15. 

Another example which uses a 1,3-butadiyne unit is given in Scheme 7.7 with the synthesis of l,8-diazacydotetradeca-3,5,10,12-tetraynes (27) [39]. In this proto-... 

To prepare cyclic tetraynes consisting of 1,4-donor-substituted butadiyne units one can use the Glaser type coupling of terminal dithiadiynes 28(3) or 28(4) (Scheme 7.8). This method produces the 18- and 20-membered rings 29(3) and 29(4), respectively, but no trimerization products were found [40]. 

To prepare macrocycles with three 1,4-donor-substituted butadiyne units the synthesis commences with the stable, commercially available bis-trimethylsilyl pro-... 

Scheme 7.9. One-pot synthesis of macrocycles with 1,4-donor substituted butadiyne units, (a) MeLi/LiBr, THF, -78 °C to rt,...

The 1,3-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). 

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. 

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