A-nitrosoamides

Other methods of converting amides to esters have been described (78). Alkyl haUdes can be treated with amides to give esters (79). Also, esters can be synthesized from A/-aIkyl-A/-nitrosoamides, which are derived from the corresponding amides (80). 

Scheme 11.11 gives some representative preparative reactions based on these methods. Entry 1 is an example of the classical procedure. Entry 2 uses crown-ether catalysis. These reactions were conducted in the aromatic reactant as the solvent. In the study cited for Entry 2, it was found that substituted aromatic reactants such as toluene, anisole, and benzonitrile tended to give more ortho substitution product than expected on a statistical basis.180 The nature of this directive effect does not seem to have been studied extensively. Entries 3 and 4 involve in situ decomposition of A-nitrosoamides. Entry 5 is a case of in situ nitrosation. 

Nitrosyl ligands have relatively poor fx-donor capabilities, but are excellent rr-acceptors. There are synthetic routes to nitrosyl complexes using NO gas, [NO][Bp4] or [NOJIPFg], hydroxyamine hydrochloride, HNO3, NaN02, or A -nitrosoamides. 

Amidyl Radical Cyclizations from A-Halo- and A-Nitrosoamides. 35... 

A-Substituted amides can be converted to A-nitrosoamides, which are more easily hydrolyzable than the orginal amide. For example, see Rull, M. Serratosa, R Vilarrasa, J. Tetrahedron Lett. 1977,4549. For another method of hydrolyzing A-substituted amides, see Flynn, D.L. Zelle, R.E. Grieco, PA. J. Org. Ghent. 1983, 48, 2424. 

Under alkaline conditions, on the other hand, diazenols and diazenolates may also be involved, in particular, as well known for diazoalkane formation via the N-alkyl-A -nitrosoamides, -urethanes and related A -nitroso compounds (see Sect. 2.4). The intermediacy of diazenolates already has been observed qualitatively by Hantzsch and Lehmann (1902). The investigation of hydrolytic partitioning of alkyl-diazenolates into diazoalkanes and dediazoniation products (4-15) was started by Moss (1966) and Kirmse and Wachterhauser (1967). With R = methyl, benzyl, or allyl in (4-15), the diazoalkane is the main product with R = alkyl a rather even partition between the two pathways was found secondary alkyldiazenolates gave almost exlusively dediazoniation products. It is interesting to note that most of the investigations were carried out in the years in which primary interest on these reactions concentrated on carbocation chemistry and less on diazoalkane formation (see, e.g., review by Moss, 1974). We refer also to the corresponding discussion (Sects. 7.2-7.5). 

In 1981, Isenring and Hofheinz discovered that diphenylmethyl isocyanide can act as a CIC when the Ugi product was treated with N2O4 in CHCI3 at 0°C and warmed to room temperature [36]. The Ugi product a-acylaminoamide 71 forms a nitrosoamide intermediate 72, which converts slowly into the diazo species 73... 

Nitrosating agents such as nitrous acid, dinitrogen trioxide, dinitrogen tetraox-ide, nitrosyl chloride, and alkyl nitrites are sources of NO (nitrosonium ion), which react with secondary amines to yield the corresponding A-nitrosamines. Similarly, secondary amides yield their corresponding A-nitrosoamides, ureas yield 7V-nitrosoureas, and carbamates, the 7V-nitrosocarbamates. 

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