Catalytic Asymmetric Synthesis of α‐Quaternary Proline Derivatives by 1,3‐Dipolar Cycloaddition of α‐Silylimines

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

“…More attractively, the transformation of α-imino esters can provide an easy access to various natural and unnatural α-amino acid esters [ 6 – 10 ]. Up to now, a series of nucleophilic substrates have been reported to react with α-imino esters, such as enamine [ 11 – 14 ], carbamate ammonium ylide [ 15 ], 1,3-dipolar cycle [ 16 ], boronic acid [ 17 ], acetylide [ 18 ], proparygylic anion [ 19 ] and ketene silyl acetal [ 20 ]. These resulted α-amino acid derivatives are useful building blocks in modern organic synthetic and medicinal chemistry [ 21 – 22 ].…”

Recent advances in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

“…Thus, the cycloaddition between a-silylimines derived from a-ketoesters and N-phenylmaleimide catalyzed by DTBM-Segphos/Cu I complexes provided the corresponding C-5 unsubstituted, C-2 quaternary substituted pyrrolidines in high yield and excellent enantiomeric excess. 72 Excellent results were also obtained using a,b-unsaturated sulfones as olefin partners. In this case quaternary proline derivatives were obtained after straightforward desulfonylation of the adducts (Scheme 28).…”

(R)- and (S)-2,2′-Bis(diphenylphosphino)-6,6′-dimethoxy-1,1′-biphenyl

“…A single example of Cu-catalyzed 1,3-dipolar cycloaddition of α-silylimines with vinylsulfones, where MeOBIPHEP was superior to DTBM-SEGPHOS, affording the proline derivative with 79% ee (eq 74). 99 MeOBIPHEP was also tested as organocatalyst for [3+2] cycloaddition of N-tosylimines with allenic esters (eq 75). 100 Moderate enantiomeric excess was obtained for the synthesis of functionalized 3-pyrroline, similar to the ee obtained with Binepine ligand, 101 but low reactivity was observed.…”