Reaction with CSy

Direct transformation [21] of p-lactams into the corresponding imino-p-lac-tams 19 has been effected with N-chlorosulphonylisocyanate (CSI) (Scheme 6). The reaction probably involves a [2 + 2] cycloaddition-cycloreversion sequence. The same experimental conditions applied to penam or cephem derivatives gave ring-enlarged products only [22]. Silylation of trichloroethyl 6p-phenoxyacetamido-penicillinate followed by reaction with CSI and reduction with metabisulphite yielded the bicyclic pyrimidine-2,4-dione 20a (1 1 mixture of epimers). The carboxylic acid 20b is devoid of antibiotic activity (Scheme 7). 

Homofulvenes 78 undergo a [6+2] cycloaddition reaction with CSI, and only one cycloadduct 79 is obtained from the isomeric substrates... 

Z)-Chiral )3-silylvinyl ethers also react readily with CSI to give the expected [2-1-2] cycloadductsIn contrast, the ( )-vinyl ethers, upon reaction with CSI give (E)-a,fi-unsaturated amides . 

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