Staudinger-type cycloaddition reaction

Recently, Delpiccolo and Mata have also explored the asymmetric synthesis of monocyclic 3,4-substituted (3-lactams (Scheme 3.15). They employed the same Staudinger-type cycloaddition reaction with the chiral glycine derivative, 4(5)-phenyloxazolidylacetyl chloride (72). The oxazolidinone moiety functioned effectively as a chiral auxiliary, and a small library of optically active p-lactams 75 were obtained following cleavage with 10% TFA/DCM and subsequent conversion to the methyl esters (diastereoselec-tivity ranged from 8/1 to >25/1). 

On the other hand, another [2 - - 2 - - 2]-type cycloaddition of one molecule of ketenes with two molecules of imines enters in the Staudinger reaction (Scheme 123). Podlech and co-workers. (2001JCS(P1)2566) reported their practical observation of the [2 -f 2 -f 2]-cyclization, giving... 

Cycloaddition of diverse types of ketenes and imines leading to the formation of P-lactams is reported. The reactions of chiral ketenes with achiral imines, chiral imines with achiral ketenes, chiral imines with chiral ketenes, and catalytic asymmetrical Staudinger reactions have been investigated. In general, a higher level of asymmetric induction is achieved using either chiral ketenes or chiral imines derived from chiral aldehydes in comparison to the use of a chiral imine derived from an achiral aldehyde with an achiral ketene. Both carboxylic acid chlorides and carboxylic acids themselves have been used as ketene precursors. 

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