Asymmetric Allylation of α‐Ketoester‐Derived N‐Benzoylhydrazones Promoted by Chiral Sulfoxides/N‐Oxides Lewis Bases: Highly Enantioselective Synthesis of Quaternary α‐Substituted α‐Allyl‐α‐Amino Acids

Abstract

Chiral sulfoxides/N-oxides (R)-1 and (R,R)-2 are effective chiral promoters in the enantioselective allylation of α-keto ester N-benzoylhydrazone derivatives 3a-g to generate the corresponding N-benzoylhydrazine derivatives 4a-g, with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a-b were subsequently treated with SmI2, and the resulting amino esters 5a-b with LiOH to obtain quaternary α-substituted α-allyl α-amino acids 6a-b, whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data.

Palladium‐Catalyzed Asymmetric Decarboxylative Allylation of Azlactone Enol Carbonates: Fast Access to Enantioenriched α‐Allyl Quaternary Amino Acids

“…The synthesis of zwitterionic derivatives 5 , 6 and 9 – 11 was accomplished since we wondered if this methodology could have been applied to the preparation of enantiopure fully deprotected quaternary amino acids. Recrystallization afforded optically pure ( R )‐α‐allyl phenylglycine 9 , and ( S )‐α‐allyl alanine 10 24 , while ( R )‐α‐allyl phenylalanine 5 was recovered in estimated 99 % ee (by comparison with reported specific rotation data). The same procedure allowed attaining the previously unreported methionine derivative 11 in almost enantiopure form, as indicated by comparison of its measured and predicted specific optical rotations.…”

“…For this purpose, we exploited the ring‐opening of the azlactone ring under acidic conditions to convert the phenylalanine‐derived 4‐allyl oxazolones 3b , 3e , and 3f into the corresponding zwitterionic amino acid 5 (Scheme ). The aforementioned reaction allowed the attainment of the zwitterionic α‐allyl valine 6 starting from the parent allylated azlactone 3c , though the α‐allyl phenylglycine methylester 7 was prepared through ring‐opening of 3g followed by diazomethane esterification of the obtained quaternary amino acid. The known N ‐benzoyl alanine derivative 8 [13b] was synthesized by performing a basic hydrolysis of 3a , while the methionine‐derived azlactone 3d was transformed into the corresponding N ‐Bz quaternary amino ester 3ds through methanolysis of the azlactone ring.…”

“…The spectroscopic data of compound 9 were matched with literature values. [23a] The product was crystallized from EtOH/H 2 O (10:1.5) to afford racemic 9 (23 mg, 24 %). The mother liquors were evaporated in vacuo to attain the desired optically pure ( R )‐enantiomer (73 mg, 76 %).…”

“…[ α ] D 22 = –15.3 (0.5 c, 1 n HCl), Lit. ( S )‐enantiomer[23b] [ α ] D 22 = +12.6 (0.5 c, 1 n HCl). Melting point: 188–190 °C.…”

Mechanisms of L‐lysine extraction with sec‐octylphenoxy acetic acid in sulfonated kerosene

“…There are four theories on the extraction mechanisms of amino acids including electrostatic interaction, Lewis acid–base interaction, proton transfer reaction and complexation extraction . The electrostatic interaction was involved in many amino acids extraction either using acidic extractant (e.g.…”