An efficient, three-step synthesis of N-vinyl-2-azetidinones 7 selenylation, and finally m-CPBA treatment, afforded Nvinyl-2-azetidinones 7 in fair to excellent yields, with starting from αor β-amino ester imines 4 has been developed. Staudinger reaction between imines 4 and a retention at the remaining stereocenters of the starting material. Two examples of the use of compounds 7 to prepare ketene precursor gave 2-azetidinones 5. Enolate formation on the amino ester moiety of the 2-azetidinone 5, bi-and tricyclic 2-azetidinones are presented.
Scheme 1 eoselective route to N-vinyl-2-azetidinone derivatives was needed. Different approaches to this type of 2-azetidinone derivative are known. They are obtained mainly from penicillin derivatives by ring fission followed by basic isomerization. [5] Alternative routes to these compounds are the functionalization of 2-azetidinones having appropriate chains tethered to the lactam nitrogen. Examples are the intermolecular carbene insertion of β-oxodiazo esters into the NH lactam bond, as catalyzed by Rh 2 (OAc) 4 , [6] the enolization of N-1,3-acetal esters by TFA, [7] and the generation of transient N-vinyl-2-azetidinones from β-lactams derived from amino esters, especially serine [8] and threonine, [9] 2-amino-1,3-propanediols, [10] allylamine, [11] and β-hydroxyamines. [12] On the other hand, the N-vinyl moiety can be incorporated into the β-lactam nucleus by treating a ketene precursor with an appropriate 2-aza-1,3-diene derivative. [13] However, the major drawback of the existing routes for preparing N-vinyl-2-azetidinone derivatives is that they are designed to accomplish the synthesis of a defined product, Results and Discussion and many of them lack the necessary versatility, especially in the introduction of the carboxy group contiguous to the 2-Azetidinones 5 were prepared by standard Staudinger lactam nitrogen, which is a characteristic of active β-lactam reactions. [16] A series of imines 4a؊g derived from β-alaantibiotics. [14] We report herein the successful development nine, -alanine, -serine, and -aspartic acid methyl esters, of a three-step synthesis of N-vinyl-2-azetidinones, both in prepared in quantitative yield by condensation of various racemic and optically pure form, starting from imines dealdehydes with the corresponding amino ester in CH 2 Cl 2 in the presence of MgSO 4 , [17] were treated, without further [᭛] For a preliminary communication of a part of this work, see:
B.