Cyclooctyne, structure

The behavior of the Si—P 7r-bond toward a G=C triple bond was examined in the case of 15a by employing differently substituted alkynes.14 It appeared that 15a does not react with dialkyl, diaryl-, or disilyl-substi-tuted alkynes at 110°C even cyclooctyne, usually a very reactive alkyne, does not react. However, when 15a was stirred with phenylacetylene at 80°C in toluene, the C—H insertion product 24 was isolated as colorless crystals (Eq. 9).14 Its molecular structure has been elucidated by singlecrystal X-ray diffraction (Fig. 9). 

Due to molecular strain, cyclooctyne is a very reactive species. Its reactions with azides proceed rapidly even at room temperature making it a convenient tool for probing structures of unstable azides. Thus, the reaction of cyclooctyne with diazide 1061 carried out in GH2CI2 at room temperature is accomplished within 2h and provides ditriazolyl derivative 1060 in 76% yield. A similar reaction of cyclooctyne with diazide 1062 leads to ditriazolyl derivative 1063 in 90% yield (Scheme 175) <2005T8904>. 

The cyclic diyne (55) has C—C=C angles of 159.3° as determined by an X-ray analysis, which is close to the value found in cyclooctyne by electron diffraction 161 (see above). The carbon framework of the molecule is almost planar with the two CH2—CH2 units in an almost eclipsed arrangement. This and the transannular repulsion between the ii-moieties leads to the large value of 1.57 A for the C3—C4 single bond. All other structural parameters seem to be normal.164)... 

The rate of the hydrogen transfer reaction depends on the structure of the alcohol, amine or thiol as well as on the structure of the cycloalkyne. Cyclooctyne (14) dehydrogenates ethanol, but the reaction is 102—103 times slower than with (31)213). The half-lives of some dehydrogenation reactions are given in Table 12 208). 

The thiirene 6 was proposed as an intermediate in the formation of a cycloadduct 23 obtained from the reaction of a thiophene endoperoxide 36 <1996CC177> and cyclooctyne under thermal conditions (Scheme 6). The structure of 23 has been verified by X-ray crystallography <2002JA8316>. 

On oxidation of 1,2-cyclooctanedione dihydrazone with HgO, cyclooctyne and Hg derivatives of triazoles have been identified. The major product is C32H42NeHg, which was assigned the structure shown (68LA(716)ll). Cyclometallations of 2-aryl-4,5-dimethyl-l,2,3-triazoles occur with Pd(II), Pt(II), Rh(II) and Ir(III) chlorides (78MI4lio5). The triazole acts as an N—C-chelate ligand. 

Taking in account the composition of the commercial mixture 45 + 46 (35% cis, 65% trans), of the anti addition of Br2, of the structure of 50 and 49 as well as their formation ratio, we can say that the first eliminations of H-Br are anti. Thus the second eliminations of H—Br have to be anti from 50 and syn from 49. Comparative experiments showed that r-BuONa alone and less efficiently NaNH2 alone in THF are able to give the anti-eliminations but not the syn ones. On the contrary, NaNH2-f-BuONa in the same solvent is able to perform all the reactions. The side reaction with complex base is still isomerization of 51 to 52. An application of this study was the preparation of cyclooctyne with 30—35% yield35. ... 

Fig. 7 Relationship between nature of the azide, structure of cyclooctyne and reaction rate constants. Reaction rate constants were determined in CD3CN D20 = 3 1...

For these reasons, we embarked on a study to determine the reaction rate constants of the most commonly applied dibenzoannulated and aliphatic cyclooctynes, respectively DIBAC and BCN, as deduced from a SciFinder structure search of these compounds. As becomes clear, since the year of its inception (2010), DIBAC has made its appearance in 260 unique publications (184 scientific publications and 80 patent applications) while BCN is reported 155 times (103 papers and 51 patent application). For comparison, DIBO, the third-most popular cyclooctyne gave 135... 

Domnin NA (1938) The triple bond in carbon rings and the probable structure of the simplest cyclic hydrocarbon of the composition C H2 .4. II. Synthesis of cyclooctyne. J Gen Chem USSR 8 851-868... 

Figure 1.13 (a) Strain-promoted azide-allgme (ycloaddition (SPAAC) between an azide and cyclooctyne. (b) Chemical structures of the azophiles OCT, MOFO, and DIBO, frequendy used in SPAAC. ... 

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