Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Retracted: Enantioselective Radical Addition to Ketimines: A Synthetic Route Towards α,α‐Disubstituted α‐Amino Acids

“…Even though various chiral phase‐transfer catalysts (PTC) have been developed for the synthesis of α,α‐disubstituted amino acids, only the copper(II)‐salen complex12 and Muraoka’s catalyst13 provide α,α‐disubstituted amino acids with two primary alkyl substituents at the α‐position. However, even those PTCs do not satisfactorily synthesize α,α‐disubstituted amino acids possessing at least one branched substituent at the α‐position.…”

Synthesis of Chlorinated Biphenyls by Suzuki Cross‐Coupling Using Diamine or Diimine‐Palladium Complexes

“…Due to this complexation‐ability these ligands are currently most intensively studied classes of chiral Schiff bases. Moreover, Salen‐type complexes often promote the reaction under very mild conditions16 and are excellent catalysts for a large group of different reactions such as epoxidations of alkenes and styrenes,9,15 alkylations,16 oxidations,13 cyclopropanations,15 Michel reactions,11 Diels–Alder reactions,10 Strecker reactions,17 and addition of Et 2 Zn to benzaldehyde 15. However, according to the best of our knowledge, only some complexes of this type have been tested for Suzuki cross‐coupling reactions.…”

Asymmetric Catalysis of Carbon-Carbon Bond-Forming Reactions Using Metal(salen) Complexes

“…The enantiomeric excess of product 42c (R¢ =CH 2 CH=CH 2 ) could be increased by increasing the amount of catalyst (Table 7, entries 8, 9), though it remained relatively low. 53,55 Valine derivative 41d, which is amongst the most hindered possible substrate for this type of alkylation reaction, showed no reaction under the standard condition. Even increasing the reaction time to seven days or the amount of catalyst to 10 mol% was unsuccessful in this case (Table 6, entries 10, 11).…”

“…However, it was still possible to obtain both a-benzyl and a-allyl aminobutyric acid derivatives with 80-82% enantiomeric excess. 53,55 Scheme 11…”