Cyclization of 3-amino esters

Carboxylic amides or related substrates, substituted with leaving groups at the /3-position, are suitable substrates for the synthesis of azetidin-2-ones. Relatively stable or labile, in situ generated, leaving groups can be applied. Selective activation of 3-hydroxy-2-hydroxymethyl-2-methylpropanamide 388 with P(NMe2)3-KPF6 and subsequent 

The amides derived from /3-hydroxy-a-amino acids, obtained from the reaction of the latter with resin-bound hydroxylamine, have been cyclized under the Mitsunobu conditions to afford 3-aminoazetidin-2-ones. The free azetidin-2-ones were cleaved from the resin by reduction with samarium iodide 20010L337 . 

The cr,/3-unsaturated amides 396 (where R = aryl or heteroaryl) cyclized in the presence of sodium acetate and iV-bromosuccinimide, presumably through the bromonium ion intermediate 397, to furnish N-unsubstituted 

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In 2004, (3-lactams were obtained by the cyclization of (3-amino esters [231]. The treatment of the latter with 10% Pd-C in the presence of ammonium formiate for 3 h, followed by silylation of the resulting hydroxyl esters gave the silyloxy esters that were subjected to cyclization using the Breckpot reaction [232, 233] to give the (3-lactams (Scheme 106). 

P-Lactams. The cyclization of )3-amino esters is induced by /-BU3AI. Although the yields are not high, many functional groups are tolerated. 

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