Photochemical synthesis of azetidin-2-ones

The photochemical generation of metal-bound ketenes from carbene-chromium complexes and the subsequent coupling with imines to give azetidin-2-ones is treated separately (Section 2.01.3.10.5). 

An asymmetric photocyclization of a-oxoamide 440 in solid state afforded azetidine-2-one 441 (Equation 176) 1996J(P2)61 . The substrate with a chloro group on either ortho- or para-position of the phenyl ring, however, afforded a racemate. Photocyclization of the phenylglyoxamides 442 of enantiomerically pure a-amino acid methyl esters produced azetidin-2-ones 443 and 444 in moderate to high diastereoselectivity, with the m-isomer as the major component (Equation 177) 2002SL131 . 

A solid-state photochemical reaction of A,iV-dialkylarylglyoxamide carrying an ionic chiral auxiliary yielded 

1- isopropyl-3-hydroxyazetidin-2-one with high enantioselectivity 2001S1253 . Irradiation of inclusion crystals of 

The photoreactions of iV-(trimethylsilyl)methyl- or iV-(tributylstannyl)methyl-substituted a-ketoamides resulted into the formation of complex mixtures including azetidin-2-ones and oxazolidinones with or without the trimethylsilyl or tributylstannyl moiety 2004JOC1215 . It was observed that the reaction of A-(trimethylsilyl)methyl-substituted a-ketoamides proceeded by competitive hydrogen abstraction and sequential single electron transfer (SET)-desilyla-tion pathways, whereas the reaction of iV-(tributylstannyl)methyl-substituted a-ketoamides preferred the sequential SET-destannylation pathway. 

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