Samarium‐Promoted Asymmetric Aldol–Tishchenko Reaction: Synthesis of Amino Acid‐Derived 4‐Amino‐1,3‐diols

A samarium‐mediated novel synthesis of enantiopure 4‐amino‐1,3‐diols is carried out through a samarium‐promoted aldol–Tishchenko reaction starting from chiral α′‐amino‐α‐chloro ketones (derived from natural α‐amino acids) and aldehydes. The process takes place with moderate levels of stereoselectivity and in high yields. A mechanism is proposed to explain these results while the absolute configuration and structure of the aldol–Tishchenko adducts were established by X‐ray analysis. This method has also been utilized for the synthesis of enigmols, 1‐deoxysphingoid base analogues.     

The Addition Reaction of Samarium Enolates and 2‐Haloenolates Derived from Esters,and Amides to Imines. Totally Stereoselective Synthesis of Enantiopure 3,4‐Diamino Esters or Amides

The addition reaction of samarium enolates and 2‐haloenolates derived from esters and amides to imines takes place in an efficient manner. A novel protocol to perform the addition reaction of samarium enolates derived from esters or amides to chiral 2‐aminoimines, with total stereoselectivity and without racemization, is also reported. The use of samarium enolates in place of other classic metallic enolates (lithium, magnesium, etc.) could be a valuable alternative to obtain enantiopure 3,4‐diamino esters or amides, when enolates of low basicity are necessary.     

Asymmetric Aldol Reaction of 3‐Acetyl‐2H‐chromen‐2‐ones and Isatins Catalyzed by a Bifunctional Quinidine Urea Catalyst

The asymmetric aldol reaction of 3‐acetyl‐2H‐chromen‐2‐ones and isatins has been realized by using a bifunctional quinidine‐derived urea as the catalyst. The corresponding 3‐hydroxyoxindole derivatives containing a 2H‐chromen‐2‐one moiety were obtained in good yields and high enantioselectivities. When (Z)‐ethyl 2‐benzylideneacetoacetate was used as the substrate, a mixture of two diastereomers (both Z and E) was obtained due to isomerization of the double bond under the reaction conditions.

     

Catalyzed Reactions of Enol Ethers with SN1 Active Groups: A Novel Method for the Preparation of α‐Alkylated Ketones

The performance of tert‐alkylations, alkoxyalkylations, and aldehyde enolate allylations proceeding with low catalyst loading (0.1 mol %–5 mol %) is described. The reactions are complete within short times and can even be performed without solvent and under ambient conditions. The mechanism of the reaction was investigated by deuterium labeling and cross‐over studies.