Hex-3-ene-l,5-diyne

Fig. 1 summarizes cyclizations of the two prototype molecules, (Z) hex-3-ene-l,5-diyne and (Z) hept-3,5,6-triene-l-yne. In all of these processes, bonds are formed from in-plane 7t-orbitals in the presence of an orthogonal 7i-system. However, it is clear that the properties of the newly formed cyclic conjugated systems can be quite... 

Fig. 16 (a) Comparison of potential energy profile for the formal Cope rearrangement of 3,4-difluorohexa-l,5-diyne-3-ene with that of (Z)-hexa-l,5-diyne-3-ene, (b) Rehybridization in the C(F) bond along the reaction path. EDI = 3,4-difluoro-hex- 3-ene-l,5-diyne ED2 = 1,6-di-fluoro-hex-3-ene-l,5-diyne BZY = difluoro-l,4-didehydrobenzezne TSBC = the transition state for the Bergman cyclization TSRBC = the transition state for the retro Bergman cyclization. 

Elimination of sulfonic acids. Double bonds can be introduced into organic molecules by elimination of sulfonic acids from the corresponding sulfonic acid esters. The reaction proceeds particularly smoothly using DBN or DBU as reagent. Thus, treatment of 3-tosyloxyhexa-l, 5-diyne (10) with excess DBN in ether at room temperature (1 hr.) affords a 40 60 mixture of cis- and fra s-hex-3-ene-l,5-diyne (11 70%).2... 

Hexadehydro-[ 18]annulene 80>, 15, (see Table 4) possesses no inner protons and the six equivalent outer protons resonate at t 2.98. This represents a downfield shift of over 1 ppm from a model compound, cis-hex-3-ene-l,5-diyne, 9, (t 4.11). This model compound also served to clarify the interpretation of the singlet at t 5.55 in the case of l,5,9-tridehydro-[12]annulene, 1, a molecule for which aromaticity is not predicted. The downfield shift of 15 and the upfield shift of 1 from the acyclic model can then be attributed to a diamagnetic ring current in 15 and a paramagnetic ring current in 1. 

Bergman and coworkers initially studied the cyclization of enediynes more than two decades ago [5, 33], The parent compound of these systems, (Z)-hex-3-ene-l,5-diyne (100) cyclizes at elevated temperatures to afford the 1,4-didehydrobenzene diradical 6 (Fig. 8). 

Bis-(4,4-ethylenedioxycyclohexyl)hexa-l,5-diyne-3,4-diol (mixture of isomers) in abs. pyridine added dropwise at room temp, to diphosphorus tetraiodide in GS2, stirred 2 hrs. at room temp., then GS2 removed by distillation during 1 hr. fran5-3,4-bis-(4,4-ethylenedioxycyclohexyl)hex-3-ene-l,5-diyne. Y 43%. H. Inhoffen et al., A. 884, 24 (1965). 

The use of the unusual spacer, -hex-3-ene-l,5-diyn-diyl, has been reported recently for the construction of polymetallic assemblies (105 R= H, OMe X = H, Ru2(X-ap)4>. Voltammetry experiments were used to confirm the conjugation through the unsaturated spacer and the materials were found to show promising magnetic and (molecular wire) charge-transfer properties. 

Figure 4 Transition structure for the ring closure of hex-3-ene-l,5-diyne...

A sharp change in the kinetics of Bergman cyclization was described [395] on the formation of metal ion chelates of acyclic enediynes. The metal was coordinated with bisphosphine 3.877 which was synthesized from the known l,6-bis(trimethylsilyl)-hex-3-ene-l,5-diyne 3.878 by desilylation followed by phosphorylation with chlorodiphenylphosphine in the presence of potassium er butoxide (Scheme 3.118) [24a, 395bj. 

---