Heterocumulenes reaction with aminals

In the case of amine nucleophiles, the products from the reaction with co-ordinated cyanates are carbamates or ureas (Fig. 4-34), and this provides a particularly convenient method for the preparation of carbamate complexes. An example of this behaviour is seen in the reaction of 3,5-dimethylpyrazole with cyanate in the presence of copper(n) salts (Fig. 4-35). Similar reactions are observed with co-ordinated thiocyanates and other heterocumulene s. 

Examples of five-membered heterocyclic rings prepared by aza-Wittig and related methods include the alkaloid leucettamine B (206) and pyrrolo[2,3-b]pyridines (207) (Scheme20). The aza-Wittig reactions of the iminophosphorane (208) with methyl isocyanate, carbon dioxide, or carbon disulfide give heterocumulenes (209), (210), and (211), respectively, which react with amines or ammonia to provide a route to the framework of aplysinopsin alkaloids (212). ... 

Methylenecyclopropanes have been carboxylated with gaseous carbon dioxide in the presence of a stoichiometric amount of nickel(O) complexes [150]. Depending on the polarity of the reaction solvent and the nature of amine ligand (amidine or guanidine base), several reactions pathways have been observed, which may involve either oxidative coupling of CO2 with the C-C double bond of the substrate (see Sect. 5.3) or opening of the three-membered ring and further reaction with the heterocumulene. 

The reactivity of hydrido(ethoxo) complex 4 was examined (Scheme 6-15) [8]. Metatheses similar to those postulated for alcohol exchange (Eq. 6.5) occurred between HCl, LiCl, phenyl acetate or primary amines and yielded complexes 94. The reaction of 4 with cyclic anhydrides proceeded similarly to give iridium-assisted ring opening products 95. Heterocumulenes afforded the inserhon products 96 into the Ir-O bond. 

Attempts to initiate formation of a nitrene, and its rearrangement to the iminooxo-phosphorane 80, by subjecting l-chloroamino-2,2,3,4,4-pentamethylphosphetane 1-oxide to a-elimination with sodium methoxide proved unsuccessful48). In contrast, however, the phosphorylhydroxylamides 88 rearrange in the presence of tert-butyl-amine to the heterocumulene 89 and then add base to give the phosphonic diamides 90 (>90%)49). The reaction is reminiscent of the well-known Lossen degradation. 

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