Iminoiodinanes reagents

Preliminary efforts to examine the mechanism of C-H amination proved inconclusive with respect to the intermediacy of carbamoyl iminoiodinane 12. Control experiments in which carbamate 11 and PhI(OAc)2 were heated in CD2CI2 at 40°C with and without MgO gave no indication of a reaction between substrate and oxidant by NMR. In Hne with these observations, synthesis of a carbamate-derived iodinane has remained elusive. The inability to prepare iminoiodinane reagents from carbamate esters precluded their evaluation in catalytic nitrene transfer chemistry. By employing the PhI(OAc)2/MgO conditions, however, 1° carbamates can now serve as effective N-atom sources. The synthetic scope of metal-catalyzed C-H amination processes is thus expanded considerably as a result of this invention. Details of the reaction mechanism for this rhodium-mediated intramolecular oxidation are presented in Section 17.8. 

High yields are obtained with iminoiodinane reagents, however, they cannot be stored and must be used immediately [15]. Moreover, they are tedious to purify, as they form polymeric structures and are insoluble in most organic solvents. Besides tosyl- and nosyl-substituted iminoiodinanes, others are almost impossible to isolate in pure form. It is to overcome these problems that one-pot processes in which the iminoiodinane species is prepared in situ rather than being isolated, have been developed. Che first demonstrated such a reaction for an intermolecular C H insertion (Eq. (5.3)) [31, 32]. The reactive metal nitrene species is generated from a mixture of the requisite amine with diacetoxyiodobenzene, in the presence of manganese porphyrin catalyst. 

A new iminoiodinane reagent for the Evans copper-catalyzed aziridination was developed (eq 24). This [fV-(alkylsulfonyl)-imino]phenyliodinane (22) is synthesized from SES-NH2 (19)... 

The C-H insertion of alkyl sulfonamides using hypervalent iodine reagents in the presence of a transition metal catalyst was initially disclosed by Dauban and Dodd <20000L2327>. In this report, sulfonamide 204 was treated with PhI(OAc)2 and base to form an intermediate iminoiodinane 205 (Scheme 28). The material 205 was first... 

Later, MacMillan and Lee [176] found that hypervalent iodine reagents were also suitable oxidants for the asymmetric epoxidation of enals, using the imidazolidinone catalyst 109 (Scheme 12.31). Optimal results were obtained by controlled release of monomeric iodosobenzene from an iminoiodinane source (NsNIPh) and a mild acid (AcOH). 

The development of in situ procedures to prepare iminoiodinanes from amine precursors and hypervalent iodine reagents has had a significant impact on the progress made towards C—H amination reactions. However, there are some drawbacks associated with the use of hypervalent iodine reagents, in particular, their cost... 

As an alternative to organic azides and iminoiodinanes, N-haloamine salts [RN(X)M] constitute a family of Nj-transfer reagents. Among the haloamine salts available, chloramine-T (TsNCINa) has been exclusively utilized for the aziridination... 

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