1.2- bis acetylene

A similar synthesis starts from commercially available 1,5-hexadiyne and 2-methyl-cyclopent-2-enone. The benzocyclobutene is obtained from a bis-acetylene in a cobalt-catalyzed reaction. It rearranges regio- and stereoselectively to a 3-deoxy steroid derivative. The overall yield from the cyclopentenone was 40% (R.L. Funk, 1977). 

The two reactions described above can be applied for the synthesis of symmetrical -acetylenes only. Unsymmetrical bis-acetylenes can be prepared by using the Cadiot-Chodkiew icz reaction For that method a terminal alkyne 1 is reacted with a bromoalkyne 8 in the presence of a copper catalyst, to yield an unsymmetrical coupling product 9 ... 

Knochel and co-workers employed the base-mediated cyclization of 2,6-diamino-3,5-dialkynylpyridines in the synthesis of bis-pyrrolopyridine 95 from bis-acetylene 94 (Equation 21) <2003PS(178)1781, 2003T1571>. 

TABLE 1. Enthalpies of formation of bis-allenes, the related bis-olefins and bis-acetylenes and their acyclic analogs... 

We can narrow the difference from 10 kJmol-1 even further once it is remembered that in the comparison of meso-bisallene, 27, and (Z, Z)-diene, 29, there are two extra alkylallene and alkylolefin interactions for which a stabilization of ca 3 kJ mol-1 for the latter was already suggested. Admittedly, comparison with the corresponding 1,5-cyclooctadiyne suggests strain-derived anomalies. From the enthalpy of hydrogenation, and thus derived enthalpy of formation, of this diyne from W. R. Roth, H. Hopf and C. Horn, Chem. Ber., 127, 1781 (1994), we find 1/2S (bis-allene, bis-acetylene) equals ca — 80 kJ mol-1. We deduce that the discrepancy of this last 5 quantity from the others is due to strain in the cyclic diyne. 

The coupling of trimethylsilylacetylene with 2,5-diiodo-l,3,4-trimethylpyrrole (121) affords the corresponding bis-acetylene after cleavage of the TMS groups [85]. 

Bis-acetylene synthesis from alkynyl halides and alkynyl copper reagents. Cf. Castro-Stephens reaction. 

The reactions of acetylenes and of unsaturated metallacycles present a large and difficult field The high reactivity of the species involved gives rise to a rich and diverse chemistry but this does not make mechanistic interpretation any easier. As is well known , the bis (acetylene) - cyclobutadiene interconversion is difficult to rationalise, but nonetheless it does take place ... 

Amino acids in general Crown ether and open chain polymer of transtetra-hydro furan, 2,5-bis acetylene unit SLM Highly selective separation and enantiomeric resolution [98,99]... 

Novel polymers have been prepared by the Diels-Alder reaction of two bis(isobenzofuran)s and a series of bis(acetylene) imides. Bis(isobenzofuran) 317 was prepared from phenylphthalide precursors. Two varieties of bis(acetylene)s 318 and 319 were prepared by the reaction of various aromatic anhydrides with amine 320 (Equation 7) or by the reactions of various diamines 321 with 4-phenylethynylphthalic anhydride 322 (Equation 8). One example of the polymers formed is 323 (Equation 9) <2000MI299>. 

The use of inorganic supramolecular compounds in catalysis has also been successful in recent years. Hupp etal. incorporated a Mn(IIl)-porphyrm (see Porphyrin) epoxidation catalyst inside a molecular square, a system that shows enhanced catalyst stabihty and substrate selectivity as compared to the free catalyst. In another example, chiral metaUocyclophanes were constructed from Pt(PEt3)2 units and enantiopme atropoisomeric t,t -binapthyl-6,6 -bis-(acetylenes) and used in enantioselective diethyl zinc addition to aldehydes to afford chiral secondary alcohols. The first organometaUic triangle based on Pt(II) and alkyne-di-substituted-binaphfhyl system was reported and found to effect asymmetric catalysis reactions of aldehydes to alcohols with excellent conversion rates and enantiomeric excess/ ... 

An elegant use of bis-acetylenic ketones (e.g. 213) in the synthesis of 1,2,4-triazepines 216 and 217 has been described <05JOC3307>. The ring heteroatoms are introduced in a one pot reaction with 213 and 214 followed by conversion of the pyrimidine intermediate 215 to 216 and 217 on reaction with trifluoroacetic acid. In contrast, reaction of 215 with TBAF gave the... 

Bis-acetylenic alcohol 1 undergoes a facile oxy-Cope rearrangement to afford mixtures of ( )-and (Z)-enynones. The latter compounds react further to give spiroannulated methylenecy-clopentenone 4 upon enolization and clectrocyclic ring closure1134. 

The formation of mono- or bis-(acetylene) complexes from the reactions of )j -CpMX(CO)3 with alkynes depends upon the acetylene substituents and the nature of the E group as it is shown in Table 1. 

The displacement of cycloocta-1,5-diene in Pt(l,5-C8Hi2) by diphenylacetylene leads to the formation of the bis-acetylene complex ... 

Fuchs has examined a number of additional alkynes. One in particular, silyl-substituted triflone 104, may prove most useful, as it provides silylated alkyne products upon reaction with suitable substrates [62c]. In general, attempts to functionalize triflones with other groups at the alkyne carbon or at propargylic positions were unsuccessful. Triflones with more remote functionality, including bis-acetylenes, gave useful reagents. Fuchs triflone methodology can also be extended to vinylation and allylation reactions (Scheme 23) [63, 64). 

A coupling reaction long used in acetylene chemistry is the Cadiot-Chodkiewicz coupling [112] its use in retinoid synthesis is demonstrated by the transformations depicted in Scheme 2-19 [113], The enyne precursor 169, on Cadiot-Chodkiewicz coupling with 3-bromo-2-propyn-l-ol (170) yields the diyne 171 which, by methodology long established in retinoid chemistry [114], may either be chain-elongated to dehydroretinal 172 or — via the diynal 173 — to the bis-acetylenic retinal 174. 

Fig. 25). Alternatively, one can "reverse the process. Porphyrin array formation can start with imidazolyl zinc porphyrin, which can be immobilized using, for example, thiolate attachment on the electrode surface [90,91]. In this case the porphyrin attached to the electrode can serve as a molecular solder connecting the electrode to polymers made of hundreds of meso-meso-or bis(acetylene)-linked bis(imidazolyl zinc porphyrins) 55 [92]. Molecular wires or light-energy conversion systems could be built on the basis of such technologies. 

The 9-membered cyclic ethers 116 have been prepared via oxy-Cope rearrangement of 115, ultimately derived from D-glucose. The 10-membered bis-ether 118 was prepared via Bergman cyclization of the bis-acetylene 117 (R=2,3,4,6-tetra-0-benzyl-p-D-glucosyl). Solution conformational analysis was reported from NMR experiments. Dialkyne 117 was prepared by Pd-catalysed coupling of the P-D-glucosyl-l-alkyne and 1,2-diiodobenzene, and a mechanism was proposed for... 

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