Rhodium catalysis nucleophilic substitution

When 6-diazopenicillanates are irradiated in the presence of sulfur nucleophiles, predominantly 6/3-substitution products are obtained (77JOC2224). When BFs-EtiO is used to catalyze the reaction with nucleophiles, however, the products are primarily the 6a-isomers (78TL995). The use of rhodium or copper catalysis led primarily to ring-opened thiazepine products, presumably by way of the intermediate (56 Scheme 39) (80CC798). 

Exposure of the (cycloalkenyl)methyl carbamates 304 to iodosylbenzene in the presence or absence of Rh2(OAc)4 gives the tricyclic aziridines 305 (Scheme 88) (02OL2137). Reactions of 305 with nucleophiles, facilitated with tosic acid or lithium perchlorate, proceed with cleavage of the C-N edge bond and afford the tf 7 z-spirooxazolidinones 306. Intramolecular aziridination of the indolyl carbamate 307 with DAIB, on the other hand, requires Rh(II)-catalysis and leads directly to the acetoxy-substituted YDi-spirooxazolidinone 308 (Scheme 88) (02OL2137). When iodosylbenzene is used instead of DAIB and alcohols are available in the reaction medium, alkoxy-substituted syn-spirooxazolidinones 309 are obtained. Whereas the conversion of 304 to 305 appears to proceed by direct cyclization of intermediate iminoiodanes, the production of 308 from 307 was attributed to the intervention of a rhodium nitrene, which collapses to 308 through zwitterionic intermediates (02OL2137). 

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