Diphenylacetylene hydroamination

Table 15.2 Group 4 metal-catalyzed intermolecular hydroamination of diphenylacetylene.

Draw a catalytic cycle of hydroamination of diphenylacetylene by an arylamine ArNH2 (Ar = 2,6-Me2C6H3) catalyzed by Cp2Zr(NHAr)2 and involving imido and azametallacyclobutane intermediates. 

Af,Af-diethylgeranyIamjne, a precursor to (—)-menthol is achieved via the hydroamination of this substrate with lithium catalysts on an industrial scale [98]. A single example of intermolecular alkyne hydroamination also exists. Thus, piperidene undergoes addition to diphenylacetylene in the presence of 10 mol% [Sr CH(SiMe3)2 2(THF)2] at 60 °C in CgDe solution over a period of 17 h a 10 1 mixture of syn- and antf-addition products are isolated consistent with an isomerization event occurring under the reaction conditions [98]. 

Common nickel compounds have been used to catalyze the hydroamination of internal activated alkenes (Scheme 3.126) [138]. The reactions were carried out under a high pressure of argon and afforded moderate yields of the enamines. While activated internal alkenes were successfully functionalized using this approach, unactivated substrates such as diphenylacetylene were unreactive and afforded low conversions (-30%). 

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