Boronic acids, carbonylation conjugate addition

Boron or tin (II) Z-enolates are generated by reaction with the corresponding triflates with a carbonyl compound in the presence of tertiary amines like r-P NEt or. M-ethylpiperidine (except when using dicyclopentylboron triflate [407]). E-Enolates are prepared by using dicyclohexyl- or other cyclic chloroboranes in the presence of Et3N or Me NEt [407, 685, 686, 1246, 1247, 1248], Because enolization does not take place under such conditions with esters or aliphatic tertiary amides, thiophenyl esters RGH COSPh have been used as ester/amide substitutes. Furthermore, Z-boron enolates of ketones can be prepared by conjugate addition of acid derivatives of dialkylboranes to a-enones [687],... 

Miyaura and eo-workers found that conjugate addition of arylboronic acids to a -unsaturated carbonyl compounds can be carried out by using cationic Pd(II) complexes such as [Pd(dppe)(PhCN)2]X2 as catalysts. Neutral Pd complexes such as PdCl2(dppe) are not active. As anions, X = C104, OTf , Bp4 , PFe", and SbFe are effective. Coordination of DPPE and PhCN is important. The reaction proceeds at room temperature in THF or dioxane, and requires the presence of water. The addition of boronic acid 48 to cyclohexenone took place to give 49 in 95% yield [18]. Also 3-phenylcyclohexanone (50) is prepared by the conjugate addition of PhSi(OEt)3 to cyclohexenone [19]. 

Occhiato and colleagues published the carbonylative coupling of lactam-, lactone-, and thiolactone-derived enoltrillates with boronic acids [29]. Several asymmetrical dienones were formed in moderate to good yields at room temperature under 1 bar of CO with 1-5 mol% of palladium catalyst (Scheme 4.14). This methodology allows for a convergent and rapid preparation of substrates, which are useful in conjugate additions and Nazarov reactions. 

The Evans mechanism for the Lewis acid-catalysed Michael addition to chiral oxa-zoUdinones and related systems has been challenged rather than chelation, open-chain mono- and bis-coordinated complexes with antiparaUel carbonyls (120) have been proposed, based on the NMR and DFT computational studies. This new mechanism is consistent with the experimental results reported for the conjugate addition of amines to a,j8-unsaturated acylimidazolidinones (119) with aluminium, boron, or zinc Lewis acids. ... 

Scheme 5.27 Pd(ll)-bpy-catalyzed conjugate addition of aryl boronic acids to a,p-unsaturated carbonyl...

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