Asymmetric cyclization via memory of chirality: a concise access to cyclic amino acids with a quaternary stereocenter.
N-(omega-Bromoalkyl)-amino acid derivatives, readily prepared from natural alpha-amino acids, gave cyclic amino acids with a quaternary stereocenter by treatment with potassium hexamethyldisilazaide in DMF. The chirality of parent amino acids was almost completely preserved during an enolate-formation and cyclization process, giving aza-cyclic amino acids in up to 98% ee in retention of configuration. This method is applicable to the asymmetric synthesis of azetidine, pyrrolidine, piperidine, and azepane derivatives. The asymmetric cyclization seems to proceed via an axially chiral enolate intermediate and not through a concerted SEi process.
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan. kawabata@scl.kyoto-u.ac.jp
Takeo
T
Kawabata
Shimpei
S
Kawakami
Swapan
S
Majumdar
D000596:Amino Acids / Q000737:chemistry; D000598:Amino Acids, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D001372:Aza Compounds / Q000737:chemistry; D003500:Cyclization; D005563:Formic Acid Esters / Q000737:chemistry; D013237:Stereoisomerism
D000596:Amino Acids; D000598:Amino Acids, Cyclic; D001372:Aza Compounds; D005563:Formic Acid Esters; C000345:t-butyloxycarbonyl group