Terminal alkynes conclusions

High yields of benzenes are formed from internal alkynes (and a few select terminal alkynes) upon heating in the presence of a soluble catalyst generated by combining Me3SiCl and Pd/C. Although neither the mechanism nor the structure of any active intermediate is known, the procedure is so simple operationally as to be the method of choice for symmetrical systems (equation 31)." Regioselectivity is mixed in the few instances reported it is impossible at this time to draw conclusions as to possible similarities with PdCb systems. 

Few studies have been conducted on the hydroformylation of alkynes. Terminal acetylenes give saturated isomeric aldehydes supposedly through the initially formed alkenes.73 Conclusive evidence was obtained that internal alkynes, in contrast, first undergo hydroformylation to yield a,p-unsaturated aldehydes, which are subsequently hydrogenated to give the saturated aldehyde end products.74... 

Analysis of 13C distribution in recovered alkynes using C4 atom as an internal standard led to experimental KIEs as collected in Table 4. For both catalysts significant isotope effect was observed for the terminal acetylenic carbon. Experimental KIEs are consistent with cyclopropenation via intact tetrabridged rhodium carbenoids and do so to support [2+2] cycloaddition. DFT calculations using B3LYP functional were complicated and did not give conclusive results. 

Zirconium Intermolecular hydroamination of both terminal and internal alkynes R C=CR with primary amines R NH2 to produce (after subsequent reduction) saturated secondary amines RiCH2-CH(NHR )R can be attained with the in situ generated zirconium catalysts (Me2N)4Zr (5 mol%) and sulfonamide (10 mol%). " Zirconium-catalysed intramolecular hydroamination (225) (226) has been studied theoretically " as for the analogous iridium-catalysed cyclization of (177) discussed (g) earlier " and similar conclusions have been reached regarding the hydrogen bonding, and so on. 

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