Dedicated to Prof. Dieter Seebach on the occasion of his 60th birthday (1 3.11.97) The [Rh,(OAc),]-catalyzed decomposition of {[(4-nitrophenyl)sulfonyl]imino}phenyl-13-iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by 0-substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron-releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral Rh" catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh-complexed nitrene into the CH bond is proposed.

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(12.VI.95)The [Rh2(0Ac)4]-catalyzed addition of methyl diazoacetate to N-benzylideneaniline (la) afforded the imine cis-2 in 35% yield. Under catalysis by chiral Rh" catalysts, however, only racemic la was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7. No aziridines were obtained, however, from lb, lc, and 3. The iminium salt 8 reacted with (trimethylsily1)diazomethane in the absence of [Rh,(OAc),] via dipolar cycloaddition followed by extrusion of Nz to 10.Aziridines are attractive intermediates in organic synthesis, and a variety of approaches to their synthesis have been investigated [ 11. The most direct access to aziridines consists of nitrene addition to olefins [2] (Scheme I ) . Systems for aziridination of olefins in the presence of chiral transition-metal catalysts have been reported from several laboratories [3-51. The decomposition of PhI=NTs by transition metals, first described by Mansuy and coworkers [3], has been successfully developed into a system for asymmetric aziridination by the groups of Evans et al. [6] and Jucobsen and coworkers [7] using chiral Cu catalysts. Aziridines are formed in high yield and with high enantiomeric excess. An alternative approach for catalytic generation of aziridines, consisting of carbene addition to imines, has been investigated in the past with limited success [%lo], and the general idea was that this was not a viable route to aziridines. R R )IVery recently, however, the Jucohsen group reported on the reactions between imines and ethyl diazoacetates in the presence of chiral Cu'-bis(dihydrooxazo1e) complexes [ 1 11. Aziridines were produced in moderate yields (10-370/0; 65 04 with an achiral bis(dihydr0-oxazole)) with ee's reaching 67 %. A mechanism involving an intermediate achiral ylide, weakly associated with the catalyst, was proposed to explain the low enantioselectivity of the carbene transfer. Asymmetric Rh-based cyclopropanation systems were also tried, but were found less satisfactory than those containing Cu. Subsequently, Ramussen and

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