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Relevant academic research and scientific papers

Stereoselective one-pot synthesis of β-lactams by Lewis acid promoted condensation of silylketenes thioacetals with imines

A series of silylketene thioacetals derived from 2-pyridylthioesters have been prepared and the (E)/(Z) configuration of some of them has been determined by NMR spectroscopy. In the presence of Lewis acids these compounds stereoselectively react with imin

Optically active aminoalcohol promoted addition of 2-pyridylthioester boron enolates to imines: Enantioselective one-pot synthesis of β-lactams

The enolates derived from 2-pyridylthioesters by treatment with BCl3·Me2S and enantiomerically pure aminoalcohols react with aromatic and heteroaromatic imines to afford β-lactams in a convenient one-pot procedure and in up to 78% e.

Synthesis of β-lactams by condensation of titanium enolates of 2-pyridylthioesters with imines. Influence of the imine structure on the trans/cis stereoselectivity

The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords β-lactams in trans/cis ratios that largely depend on the structure of the C-imine residue. Bulky and non-chelating heteroatom-containing groups lead to the formation of trans β-lactams, while sterically non-requiring or chelating groups favour the formation of the cis-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.

Synthesis of β-lactams by condensation of the tin enolates of 2-pyridylthioesters with imines. A comparison between titanium and tin enolates

Addition of triethylamine to a mixture of 2-pyridylthioesters and SnCl4 or SnBr4 affords the corresponding tin(IV) enolates that add to imines to give β-lactams in fair to good yields and with various degree of trans/cis stereoselectivity. Examples of highly diastereofacially selective reactions carried out on a chiral thioester and on a chiral imine are also reported. The results are compared with those obtained in the condensations promoted by TiCl4 and TiBr4.

N-Trimethylsilyl Imines: Applications to the Synthesis of β-Lactams

Ester enolates and N-trimethylsilyl imines react to afford N-protio-β-lactams.The stereochemical course of the reaction depends on the ester enolate geometry.Therefore (E)-enolates give mainly cis β-lactams while (Z)-enolates give nearly equal mixtures of cis and trans β-lactams.The use of ethyl β-hydroxybutyrate as the ester component allows the preparation of β-lactams of potential use in carbapenem synthesis.The differences in the behavior of N-trimethylsilyl and N-aryl imines in ester-imine condensations are also discussed.