Copper-phosphinamine

Introduced by Alexakis et al., copper-phosphinamine systems also stand out as effective catalysts for the addition of organoaluminium reagents to cychc enones [46, 47]. In many cases, and in particular with challenging substrates, phos-phinamine ligands (Fig. 4) outperform the phosphoramidite counterparts. 

Scheme 13 Copper-phosphinamine-calalysed ECA of organoaluminium reagents to p-substituted cyclohexenones by Alexakis [46,47]...

Scheme 16 Copper-phosphinamine-catalysed ECA of alkenyl aluminium reagents (prepared by hydroalumination with DIBAL-H) to P-substituted cyclic enones by Alexakis [48,49]...

General observations and limitations on the copper-phosphinamine-catalysed CA of alkenyl aluminium reagents include ... 

Scheme 24 Copper-phosphinamine-catalysed ECA of aryl aluminium reagents to p-substituted...

Fig. 4 Effective phosphinamine ligands for the copper-catalysed ECA of organoaluminium reagents to p,p-disubstituted enones...

The versatile phosphinamine ligands are also suitable for the copper-catalysed ECA of organoaluminium reagents to a,p-unsaturated lactams, including p-methyl-substituted 8-lactams, whose reaction allows the formation of all-carbon quaternary stereogenic centres in moderate yields and good enantioselectivities, as exemplified in Scheme 22 [57]. 

The copper-NHC-catalysed addition of organoaluminium reagents to cyclo-hexenones and cycloheptenones reported by Hoveyda [58] is, in some cases, slightly less selective than those performed in the presence of phosphoramidites or phosphinamine catalysts (<90% ee for the imidazolium ligands versus <99% ee that the phosphoramidites and phosphinamine can provide). However, NHC-Cu catalysis provides better results (up to 97% ee and 97% conv) when challenging cyclopentenones and bulky p-substituted cycUc enones (bearing n-butyl, alkynyl, aryl or an ester group as the p substituent) are used as substrates (Scheme 25). 

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