Cyclic diynes

Indeed, cw-l,2-divinylcyclopropanes give this rearrangement so rapidly that they generally cannot be isolated at room temperature,though exceptions are known. When heated, 1,5-diynes are converted to 3,4-dimethylenecyclobu-tenes. A rate-determining Cope rearrangement is followed by a very rapid electro-cyclic (18-27) reaction. The interconversion of 1,3,5-trienes and cyclohexadienes... 

The most remarkable structural features of the planar cyclic mixed trisethyne-monobutadiyne pentaacetylenes 181 and 62 are their drastically bowed diyne moieties [18]. The acetylenic carbon atoms deviate from linearity by an average of 11.7° in 181 and even 13.4° in 62. The internal C-C-C angle is smaller for 181 (103.8°) than for 62 (109.2°). The disparity of the C-C bond lengths in the spirocyclopropane moieties of 62 is analogous to those observed in the expanded [n]rotanes 165-168. 

The hybrid cyclic pentayne 181 underwent Diels-Alder reaction with the electron-deficient diene tetrachlorothiophene 1,1-dioxide 192, but only at one of the two triple bonds of the 1,3-diyne moiety. This was followed by loss of SO2 to give the tetrachlorobenzannelated cyclotetradecenetetrayne 193 (Scheme 37) [18]. 

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. 

NbBrs, and NbCls-Pl Sn evidently proceeds via cyclotrimerization of diynes, which most probably involve cyclic carbometallation, details are not very clear.246 2463 Related reactions of Ta and Mo complexes were also investigated in this study. Formation of tantallacyclopropenes by complexation of alkynes with Ta complexes has also been reported247 (Scheme 51). In addition to the Ta-catalyzed polymerization of diynes mentioned above, Ta-catalyzed or -promoted cyclotrimerization reactions of alkynes to produce benzene derivatives, a Ta-promoted ethylene... 

The same type of bis-functionalization has been reported for the palladium-catalyzed borylstannylative carbocy-cyclization of 1,6-, 1,5-, 1,7-diynes, bis-propargylamine, and ether.377 It should be noted that even 1,2-dialkylidene cyclobutane can be obtained in reasonable yield. Ito has proposed the related silaborative reaction involving nickel(O) catalysis.378 This reaction has been performed in an intra- and intermolecular fashion. The intramolecular reaction allows the formation of cyclic dienes and the intermolecular process proceeds through a dimerization of alkynes to give acyclic dienes. 

Beyond palladium, it has recently been shown that isoelectronic metal complexes based on nickel and platinum are active catalysts for diyne reductive cyclization. While the stoichiometric reaction of nickel(O) complexes with non-conjugated diynes represents a robust area of research,8 only one example of nickel-catalyzed diyne reductive cyclization, which involves the hydrosilylative cyclization of 1,7-diynes to afford 1,2-dialkylidenecyclohexanes appears in the literature.7 The reductive cyclization of unsubstituted 1,7-diyne 53a illustrates the ability of this catalyst system to deliver cyclic Z-vinylsilanes in good yield with excellent control of alkene geometry. Cationic platinum catalysts, generated in situ from (phen)Pt(Me)2 and B(C6F5)3, are also excellent catalysts for highly Z-selective reductive cyclization of 1,6-diynes, as demonstrated by the cyclization of 1,6-diyne 54a.72 The related platinum bis(imine) complex [PhN=C(Me)C(Me)N=Ph]2Pt(Me)2 also catalyzes diyne hydrosilylation-cyclization (Scheme 35).72a... 

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... 

Stoichiometric bicydization of enynes, diynes, and dienes by cyclic carbozirconation... 

When the terminal alkynes 96 are treated with the trimethylsilylalkyne 97 in the presence of HfCl4 as a Lewis acid, the silylated vinylallenes 98 are produced in acceptable yields. In an intramolecular variant of this process, 100 was obtained from the diyne 99 [32]. Vinylallenes, incorporated into a cyclic framework and hence of restricted conformational mobility, are of interest for photochemical studies [33] and are among the photoproducts in ring-enlargement reactions of polycyclic allenes [34]. 

Diynes have already been used for building polycylic compounds in the presence of CO2 and a stoichiometric amount of Ni(0) bicyclic pyrones were obtained [117]. With the electrocarboxylation method, linear or cyclic mono-carboxylic acids were obtained as main products from non-conjugated diynes depending on the ligand associated to Ni [118, 119]. Thus ring-fomation occurred with the Ni-bipyridine complex at normal pressure of CO2 on the other hand, in the presence of PMDTA as ligand and with a 5 atmosphere pressure of CO2, linear adducts were mainly formed as illustrated in Eq. (16) ... 

Scheme 16.13. 9,10-Didehydroanthracene (33) was generated from various precursors, but rapidly rearranges to cyclic diyne 35.

Diynes are treated with Ic in the presence of an allylsilane to give cyclic trienes (Equation (12)). ... 

The dehydrogenative double silylation method is extended to the synthesis of fused cyclic polycarbosilanes by the condensation of various diynes with l,2,4,5-tetrakis(dimethylsilyl)benzene.62 Polymeric compounds are formed with elimination of H2 [Eq. (20)]. 

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