The Use of Samarium Enolates, A Novel Alternative in the Addition Reactions to Imines. Synthesis of 3‐Amino Esters, Amides and Enantiopure 3,4‐Diamino Esters

Abstract

An efficient reaction of tosylimines with a range of samarium enolates (derived from esters, and amides) is reported. The reaction with the a-dibenzylamino-N-tert-butanesulfinimine derived from chiral phenylalaninal afforded the corresponding enantiopure 3,4-diamino ester with very high diastereoselectivity.

SmI2-promoted imino-Reformatsky reaction for facile synthesis of enantioenriched β-amino acid esters

“…HMPA was found to have no influence on the reaction diastereoselectivity, but cause deleterious effect on yield when the amount was more than 1 equiv (entries 5-7). Decreasing the amount of tert-butyl bromoacetate or SmI 2 resulted in the lower yield of 3b (20% and 51% respectively, entries 8,9). Gratifyingly, the reaction a) Unless otherwise noted, 2 equiv of tert-butyl ester 2b was used, and the concentration of SmI 2 was 0.1 M in the reaction system.…”

“…Of the methods developed, asymmetric addition of Reformatsky-type reagents to imines is known as an attractive strategy for optically active -amino acid esters preparation. In recent years, a number of different chiral auxiliaries [8][9][10][11][12][13] as well as catalysts [14] has been introduced to provide the products with high stereoselectivities. Among them, the chiral sulfoxides are found as one of the best auxiliaries for the advantages of good stereodirecting and facile removal [15][16][17][18][19].…”

“…Among them, the chiral sulfoxides are found as one of the best auxiliaries for the advantages of good stereodirecting and facile removal [15][16][17][18][19]. In contrast to the classical Zn-induced Reformatsky protocol, the application of other metal salts such as samarium diiodide by diastereoselective samarium enolate addition has received little attention in imino-Reformatsky reaction [9]. As part of our effort to develop efficient new methods for synthesis of diverse structurally important molecules, we herein report our findings on the use of SmI 2 for asymmetric Reformatsky reaction of N-tertbutanesulfinyl imine.…”

The Fascinating Chemistry of α‐Haloamides

“…Samarium‐based enolates derived by metalation of iodoacetamide or dichloroacetamide A with samarium diiodide smoothly added to the electrophilic carbon of aliphatic aldehydes as well as of aliphatic activated aldimines affording β‐hydroxy or β‐aminoamides B and C respectively (Scheme ) –. Noteworthy, the reaction with aldehydes afforded ( E )‐α,β‐unsaturated primary amides provided that SmI 2 was used in large excess (6 equiv.)…”

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

“…Recently, we have communicated the first protocol to carry out the Mannich reaction with samarium enolates 9. Here, a range of various 3‐amino esters or amides were prepared by the reaction of samarium enolates with imines derived from p‐ toluenesulfonamide.…”