Direct Asymmetric Intramolecular Alkylation of β-Alkoxy-α-amino Esters via Memory of Chirality

The intramolecular α-alkylation of β-alkoxy-α-amino esters derived from l-serine proceeded predominantly over β-elimination. When β-alkoxy-α-amino esters were treated with powdered CsOH in DMSO at 20 °C, α-alkoxymethyl cyclic amino esters were obtained in up to 94% ee. Optically active THF amino acids were synthesized for the first time by the present method

Asymmetric Induction via Short-Lived Chiral Enolates with a Chiral C–O Axis

A novel method has been developed for the asymmetric cyclization of alkyl aryl ethers. The reactions were assumed to proceed via short-lived chiral enolate intermediates with a chiral C–O axis to give cyclic ethers with tetrasubstituted carbon in up to 99% ee. The half-life of racemization of the chiral enolate intermediate was roughly estimated to be ∼1 s at −78 °C

Asymmetric Cyclization via Memory of Chirality: A Concise Access to Cyclic Amino Acids with a Quaternary Stereocenter

N-(ω-Bromoalkyl)-amino acid derivatives, readily prepared from natural α-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

Synthesis and Determination of the Absolute Configuration of Chiral Tetracosanaphthalenes

Tetracosanaphthalenes with diethylaminocarbonylmethoxy side chains were constructed by bottom-up synthesis, and their absolute configurations were determined by an exciton chirality method

Powdered KOH in DMSO: An Efficient Base for Asymmetric Cyclization via Memory of Chirality at Ambient Temperature

Enolate chemistry has been extensively used for stereoselective C−C bond formation, in which metal amide bases are frequently employed in strictly anhydrous solvents at low temperatures. However, we found that asymmetric intramolecular C−C bond formation via axially chiral enolate intermediates proceeded in up to 99% ee at 20 °C using powdered KOH in dry or wet DMSO as a base. The enantioselectivity was even higher than that of the corresponding reactions with potassium hexamethyldisilazide in DMF at −60 °C. The racemization barrier of the axially chiral enolate intermediate was estimated to be ∼15.5 kcal/mol. On the basis of the barrier, the chiral enolate intermediate was supposed to undergo cyclization within ∼10-3 sec at 20 °C after it is generated to give the product in ≥99% ee. Thus, enolates generated with powdered KOH in DMSO were expected to be extremely reactive

Asymmetric Intermolecular Conjugate Addition of Amino Acid Derivatives via Memory of Chirality: Total Synthesis of Manzacidin A

Asymmetric intermolecular conjugate addition of α-amino acid derivatives with <b>4</b> via memory of chirality has been developed. The reactions proceeded in up to 98% ee with retention of configuration at the newly formed tetrasubstituted carbon center when R = Me. The product (R = Me) was transformed into manzacidin A

Asymmetric Intermolecular Conjugate Addition of Amino Acid Derivatives via Memory of Chirality: Total Synthesis of Manzacidin A

Asymmetric intermolecular conjugate addition of α-amino acid derivatives with <b>4</b> via memory of chirality has been developed. The reactions proceeded in up to 98% ee with retention of configuration at the newly formed tetrasubstituted carbon center when R = Me. The product (R = Me) was transformed into manzacidin A

Total Synthesis of Spirotryprostatin B via Asymmetric Nitroolefination

A total synthesis of spirotryprostatin B was accomplished via asymmetric nitroolefination as a key step

Nonenzymatic Kinetic Resolution of Racemic Alcohols through an “Induced Fit” Process

Nonenzymatic Kinetic Resolution of Racemic Alcohols through an “Induced Fit” Proces

Asymmetric Intermolecular Conjugate Addition of Amino Acid Derivatives via Memory of Chirality: Total Synthesis of Manzacidin A

Asymmetric intermolecular conjugate addition of α-amino acid derivatives with <b>4</b> via memory of chirality has been developed. The reactions proceeded in up to 98% ee with retention of configuration at the newly formed tetrasubstituted carbon center when R = Me. The product (R = Me) was transformed into manzacidin A