Manganese(III)-promoted cyclization of N-alkenylmalonamides (¼ N-alkenylpropanediamides) gave 3-(aryl/(alkylamino)carbonyl) b-lactams as well as 3-(aryl/(alkylamino)thiocarbonyl) b-lactams. The relative configuration of the obtained products was unambiguously determined by X-ray crystallography. The proposed method is very useful for the one-pot synthesis of a number of 3-(aryl/ (alkylamino)carbonyl) b-lactams, especially those containing an amino(thiocarbonyl) moiety, which are not selectively accessible by other methods.Introduction. -For the period of almost seven decades, after the first documented use of penicillin had begun, the b-lactam system has been at the center of interest of organic chemistry. Of course, the main stream of research is related to the potential applications of b-lactams as effective antimicrobial chemotherapeutics. However, purely synthetic studies are also known, for example, the Ojima b-Lactam Synthon Method for the preparation of peptides [1], amino acids [2], and hydroxy acids [3].So far, several methods for the preparation of the azetidine-2-one system have been developed, e.g., carbodiimide coupling of b-amino acids [4], condensation with PPh 3 pyridine disulfide developed by Ohno and co-workers [5], Grignard reagent-mediated cyclization of silyl esters of amino acids [6], cyclizations using an epoxide system and anion-stabilizing group [7], intramoleular electrophilic addition to olefins [8], or radical cyclization of 3-oxoenamides [9]. However, it should be noted that the first method used for the preparation of b-lactams via the cycloaddition of ketenes to imines, proposed by Staudinger at the beginning of the 19th century [10], after several modification and improvements, is still one of the most popular methods for the preparation of these compounds.Recently, we have reported a variation of the Staudinger method for the preparation of 3-carbamoyl b-lactams by addition of aldimines to carbamoyl ketenes, generated from 5-[hydroxy(arylamino)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione [11]. Despite many advantages, mainly due to the simplicity of this method, we were not able to obtain models of 3-carbamoyl b-lactams with alkyl groups or S in the carbamoyl fragment.As mentioned already, an alternative way of forming b-lactams may be the cyclization of enamides, which was demonstrated by Trogolo and co-workers [9] in the oxidative cyclization of 3-oxo enamides. On the other hand, we have recently developed a method for the preparation of N-alkenylmalonamides (¼ N-alkenylpropanediamides) and N-alkenylthiomalonamides 3 from carbamoyl and thiocarbamoyl Meldrums acids 1, respectively [12].