Ruthenium Complex-Catalyzed Reaction of Isocyanoacetate andN-Sulfonylimines:  Stereoselective Synthesis ofN-Sulfonyl-2-Imidazolines

Abstract

Ruthenium(II)-catalyzed reaction of N-sulfonylimines with methyl isocyanoacetate proceeds efficiently under neutral, mild conditions to give trans-2-imidazolines stereoselectively in high yields. 2,3-Diamino acids can be easily acquired via the hydrolysis of the imidazolines in excellent yields. A possible mechanism for the ruthenium-catalyzed aldol reaction of the imines under neutral conditions is discussed.

Stereoselective reactions with imines

“…In all cases, the trans-2-imidazolines were obtained with high selectivity and yield [6]. The results indicate that Ru(II)-complex-catalysed aldol reactions of N-sulfonylimines are highly ef®cient in yield and stereoselcetivity under neutral condition.…”

“…The imidazolines obtained by this reaction can be used in the the synthesis of various substituted 2,3-diamino acids or diamino alcohols (6), which are constituents of some peptidic antibiotics as well as other biologically active molecules. Optically pure 2,3-diamino acids can also be obtained by the simple hydrolysis and deprotection of these chiral 2-imidazolines that were upgraded by crystallisation (Scheme 4).…”

Palladium Pincer Complex‐Catalyzed Condensation of Sulfonimines and Isocyanoacetate to Imidazoline Derivatives. Dependence of the Stereoselectivity on the Ligand Effects

“…Notwithstanding, this reaction is particularly interesting, since condensation of imines with isocyanides leads to 2-imidazolines, which can easily be converted to a,b-diamino acids, which represent [43] a class of biologically important compounds. Although, this important condensation reaction could be performed using various sulfonimines (2) and isocyanoacetate (3) in the presence of gold, [44][45][46] ruthenium [47] and copper [48] catalysts, reports on palladium-catalyzed reactions are very scarce. [44,47] This can be explained by the fact that the palladium-catalyzed coupling of imines with isocyanides was characterized as a slow and unselective process.…”

“…Although, this important condensation reaction could be performed using various sulfonimines (2) and isocyanoacetate (3) in the presence of gold, [44][45][46] ruthenium [47] and copper [48] catalysts, reports on palladium-catalyzed reactions are very scarce. [44,47] This can be explained by the fact that the palladium-catalyzed coupling of imines with isocyanides was characterized as a slow and unselective process. [44,47] We have now found that palladium pincer complexes show a relatively high catalytic activity in the coupling of sulfonimines with isocyanoacetate; and that the stereoselectivity of the process is highly dependent on the electronic properties of the applied pincer complex catalysts (Scheme 1).…”

“…[44,47] This can be explained by the fact that the palladium-catalyzed coupling of imines with isocyanides was characterized as a slow and unselective process. [44,47] We have now found that palladium pincer complexes show a relatively high catalytic activity in the coupling of sulfonimines with isocyanoacetate; and that the stereoselectivity of the process is highly dependent on the electronic properties of the applied pincer complex catalysts (Scheme 1). Therefore, we have studied the synthetic scope and selectivity of this reaction employing various sulfonimines (2a-g) and isocyanoacetate 3 in the presence of catalytic amounts of pincer complexes 1a-g and a commonly employed palladium salt PdA C H T U N G T R E N N U N G (OAc) 2 (1h) affording 2-imidazoline products 4a-g [Eq.…”