Palladium(0) Olefin Complexes and Enantioselective Allylic Amination/Alkylation with a P,N-Auxiliary

Abstract

New Pd(0) olefin complexes, 2−5, of a binaphthalene-based chiral P,N(oxazoline) auxiliary, (S,R)-2-[4-(isopropyl)oxazol-2-yl]-2‘-diphenylphosphino-1,1‘-binaphthyl, 1, have been prepared (olefin = fumaronitrile, maleic anhydride, 4-cyclopentene-1,3-dione, and dibenzylideneacetone). These compounds reveal different dynamic behavior in solution as shown by 2-D exchange spectroscopy. Ligand 1 affords excellent enantioselectivity (up to 99% ee) in the allylic amination of a 1,3-diphenyl allyl precursor. The solid-state structure of [Pd(η3-PhCHCHCHMe)(1)]OTf, 15, has been determined and shows two different diastereomeric cations within one unit cell; that is both the si and re faces of the allyl crystallize together, the first example of this for a moderately large allyl ligand. The structure of PdCl2(1) is also reported and reveals (as does that for 15) that the oxazoline ring of 1 is twisted relative to the P−Pd−N coordination plane, thus placing this ring substituent above and not below the coordination plane. A more exact solid-state structure for Pd2(dba)3 has been determined.

Metal‐Catalyzed Enantioselective Allylation in Asymmetric Synthesis

“…[54,56,63,141,189,202] However, excellent regio-and stereoselectivities were observed for the reaction of 4-tert-butylphenol with unsymmetrical 1-alkyl-3-phenylallyl carbonates 142 to afford 143 a in very high yield and stereoselectvity. A complete reversal of regioselectivity was observed when aniline was used as the nucleophile, and afforded 144 b in 52 % yield and 98 % ee (Scheme 51).…”

Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

“…On the contrary, when N-N, N-S and N-P molecules are employed as ancillary ligands their 1 H NMR signals are all shifted downfield, indicating the predominant r-nature of the ensuing bonds. The formation of different isomers as a function of the olefin structure and of the symmetry of the ancillary ligand can be observed (Scheme 3) [4,30,32,34,[40][41][42][43]. Usually these species undergo extensive fluxionality and the RT 1 H NMR spectra of the complexes are characterized by rapid interconversion among isomers and only averaged spectra are detectable.…”

“…Notably, in some case it is possible to distinguish between the relative structure of the diastereoisomers by means of low temperature NOE experiments [4,41].…”

Metallkatalysierte enantioselektive Allylierungen in der asymmetrischen Synthese

“…[54,56,63,141,189,202] Die Reaktion von 4-tert-Butylphenol mit den unsymmetrischen 1-Alkyl-3-phenylallylcarbonaten 142 führte dagegen hoch regio-und stereoselektiv und mit sehr hoher Ausbeute zu 143 a. Mit Anilin als Nucleophil kehrte sich die Regioselektivität vollständig um, und 144 b wurde in 52 % Ausbeute und mit 98 % ee erhalten (Schema 51). [203] Gais et al berichteten, dass die dynamische kinetische Racematspaltung der unsymmetrischen 1,3-disubstituierten Allylcarbonate 145 a,b mit H 2 O zu den optisch aktiven Allylalkoholen 146 a,b hoch enantioselektiv verläuft, während Substrate mit R = CN oder P(O)(OEt) 2 nur geringe Enantioselektivitäten ergeben.…”