ABSTRACT
A new catalyst system for the enantioselective alpha-arylation of ketones is reported. This catalyst, prepared from Pd(2)(dba)(3) and a bulky dialkylphosphino-binaphthyl ligand, is able to effect the asymmetric arylation of ketone enolates with aryl bromides utilizing NaO(t)()Bu as base. These new catalysts enjoy much higher reactivity than previous systems; arylation reactions could be effected at room temperature with only 2 mol % of the Pd catalyst. The coupling of alpha-alkyl-alpha'-protected cyclopentanones proceeded in high yield, and the resulting quaternary stereogenic center was installed in up to 94% ee.
Subject(s)
Hydrocarbons, Aromatic/chemical synthesis , Ketones/chemical synthesis , Catalysis , Cyclopentanes/chemical synthesis , Molecular Conformation , Organometallic Compounds/chemistry , Palladium/chemistry , StereoisomerismABSTRACT
cis- and trans-2,3-Trisubstituted vinylaziridines have been prepared from cis- and trans-epoxy alcohols, respectively, and used as substrates in the aza-[2,3]-Wittig rearrangement. Five different anion-stabilizing groups have been investigated for their efficiency to promote the rearrangement, and it was found that N-tert-butyl acetyl vinylaziridines were superior in this reaction, affording the corresponding cis-2,6-tetrahydropyridines (>90%) as single isomers when treated with LDA. Similarly, the corresponding (Z)-propenylaziridines gave trans,trans-2,3,6-trisubstituted tetrahydropyridines as the sole products while the (E)-propenylaziridines afforded the cis,cis-2,3,6-derivatives with equally high selectivity. The scope and limitations of the process have been investigated by varying the structure of the substrate, and the mechanism of the rearrangement has been probed to some extent; the mechanistic picture is more complex than assumed previously.
