Transition metal-mediated cycloaddition reactions of alkynes in organic synthesis

π-Conjugated carbocycles and heterocycles via annulation through C-H and X-Y activation across CC triple bonds

“…The reaction between diethylacetylene and ortho-alkynylarylbromide 65 afforded 66 as a mixture of E-and Z isomers, and optimization of the reaction conditions is shown in the Scheme. 113 Here, the use of P(n-Bu) 3 ligand gave a better result than the use of P(t-Bu) 3 ligand and the other bulky ligands. Besides C-X/C-H activation mentioned above, if crossover annulation between arenes and alkynes via C-H/C-H activation becomes feasible, such a reaction is very desirable and ideal for constructing π-conjugated aromatics.…”

“…Accordingly, a number of structurally interesting -conjugated molecules have been synthesized in the past few years (Figure 1), 1 and new methods including transition metal-catalyzed reactions have been developed for synthesizing those compounds efficiently and easily. In general, polysubstituted benzenes can be synthesized through the transition metalcatalyzed [2+2+2] cyclotrimerization of alkynes, [2][3][4][5][6][7][8][9][10] the Diels-Alder reaction of conjugated 1,3-dienes with alkynes, [11][12][13][14][15][16][17] the dihydro-Diels-Alder reaction [18][19][20][21][22][23][24][25][26] and the [4+2] benzannulation of conjugated enynes and diynes. However, these standard benzannulation reactions have not been used so often for the synthesis of -conjugated carbo-and hetero-cycles, perhaps because those structures (as shown in Scheme 1) are too complicated, preventing the application of simple benzannulation procedures.…”

The role of ancillary ligands and of electron poor alkenes and alkynes in stabilizing Pd(0) derivatives: A comparative study

“…Owing to the great importance of palladium(0) olefin derivatives in catalysing cross-coupling [1], allyl alkylation [2], allyl amination [3] reactions and processes involving unsaturated molecules [4] we decided to carry out an exhaustive study with the aim of gaining a better comprehension of the stability of such complexes as a function of the nature of the olefin, alkyne (when possible) and ancillary ligand. Several papers have appeared in the literature dealing with the stability that deactivated olefins impart to the corresponding palladium(0) derivatives [5] and, in particular, our group determined in some cases a stability order based on the equilibrium constant of the direct exchange between olefins according to the following reaction [6a,6b]:…”

The synthesis of palladacyclopentadienyl derivatives from rigid bis-alkynes and their use as precursors in the synthesis of fluoroanthene-like cycles under mild conditions. A reactivity investigation

“…A reactivity investigation The reactions of unsaturated molecules catalyzed by palladium complexes represent an important topic in organometallic chemistry and consequently a wealth of papers have been recently published in this interesting field [1]. Moreover, exhaustive investigations on the attack of some dissymmetrically and symmetrically substituted alkynes on palladium(0) olefin derivatives to give the corresponding palladacyclopentadienyl complexes were recently carried out by Elsevier's group [2] and in our laboratory .In the latter case, the related mechanism was proposed on the basis of structural and kinetic evidence [3].…”