Alkenes nitrogenation, metal-free

Efficient aziridination could also be accomplished with the isolated bromine(lll) reagent 51 introduced by Ochiai (Scheme 12). This reagent provides entirely stereospecific metal-free formation of aziridines 53 for a series of neutral alkenes 52. As to a particularly impressive example, (Z)-stilbene 54 underwent completely selective formation of the cA-2,3-diphenyl product 55. Although its structural description follows the one discussed before for the iminoiodine derivatives, the nitrogen atom maintains suitable electrophilicity to react with alkenes to engage in the corresponding aziridine formation [41]. 

The mechanism of this reaction was discussed by the authors (Scheme 4.40). Initially, aldehydes are formed by the PIDA mediated oxidative C-C bond cleavage of 1,2-diols, which are generated from the dihydroxylation of alkenes [142]. Upon the decomposition of ammonium bicarbonate, the aldehydes could be trapped by ammonia to give imines, which would be further oxidized to give nitriles. This reaction shows the efiftciency of the combination of metal-free oxidant and inexpensive nitrogenation agent for the synthesis of nitriles, which should be of great value in further studies. 

Interestingly, the propensity of the boron atom to engage in secondary interactions was also examined by Jacobsen. The interaction of the rhodium complex 60 with a model substrate, namely 5-hexen-l-amine, was monitored by 1H NMR spectroscopy.62 The stronger upheld shifts of the alkene resonances compared to those observed upon coordination of the same substrate to the related boron-free salt [Rh(cod)(DIOP)][ClC>4] (cod = cycloocta-1,5-diene) were attributed to a cooperative behavior of the boron and metal centers of 60 that concomitantly interact with the nitrogen atom and alkene moiety, respectively (Figure 20). 

One of the many important differences between phosphorus and nitrogen chemistry is the relative strengths of their bonds to hydrogen. The relatively weak P—H bond means that this functionality can be added across a wide variety of unsaturated molecules (alkenes, alkynes, carbonyls) and hence this represents an excellent method for preparing tertiary phosphines. The addition of P 11 compounds to C=0 and C=N has been described in detail by Gilheany and Mitchell.2 The reaction can be catalyzed by base (potassium hydroxide, butyllithium), acid (HC1, carboxylic acids, sulfonic acids, boron trifluoride), free radical (uv, organic peroxides, AIBN) or metal (simple metal salts, late transition-metal complexes). In some circumstances no catalyst is required at all for P 11 additions to proceed.60... 

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