Copper-catalyzed boryl substitutions

Copper-catalyzed Boryl Substitution of Allylic and Propar-gylic Carbonates. 

Shen in 2012 reported an Ir/Cu synergistic catalytic C—H bond activation for the one-pot trifluoromethylation reaction (Scheme 9.19). This catalytic process involves sequential iridium-catalyzed C—activation borylation and copper-catalyzed trifluoromethylation of arenes with a variety of functional groups. This tandem procedure was successfully applied to the 2,6-disubstituted pyridine, benzofuran, benzothiazole, indole, and substituted quinoline systems. 

Copper(II)-catalyzed Boryl Addition to Allylic Carbonates. The conversion of allylic carbonates to chiral a-substituted allylboronates was also investigated by Hoveyda, who was able to accon ilish this transformation with a Cu(II)-NHC complex. This reaction proceeds in a vinylogous fashion to Sawamura s, but under these conditions, (E)- and (Z)-allylic carbonates undergo substitution to produce opposite enantiomers of product with similar yields and selectivity. This methodology is also tolerant of substitution at the a- or -position and is effective for di-or trisubstituted alkyl (linear or branched) or aryl alkenes delivering a quaternary a-chiral allylboronate product with up to 98% enantioselectivity (eq 49). 

The NHC-Cu-catalyzed conjugated addition of [B(pin)]2 on a,p-unsaturated carbonyl species has also been investigated. Perez and Fernandez initially reported the p-borylation of conjugated enals. Enantioselective versions of this transformation started to emerge afterwards, but the first methods that were developed exhibited only moderate ee s. Hoveyda and McQuade in 2010, and Song and Ma in 2015 reported a series of new NHC precursors that performed the same reaction on acrylates with high efficiency and selectivity (Scheme 11.6). Similar chiral NHCs were also used by Hoveyda and McQuade in the development of copper-catalyzed enantioselective allylic substitution using [B(pin)]2 as a formal pronucleophile. 

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