Application of phosphorous ylides to organic synthesis
The physical and chemical properties, and in particular, the
nucleophilicity and nuclear magnetic resonance spectra of iminophosphoranes
I-V have been studied in detail. Nmr measurements of
chemical shifts have indicated that electronic effects of substituents
on the nitrogen atom in iminophosphoranes are transmitted to phosphorus
whereas such interaction is prevented in N-alkylated salts such as VI.
Basic hydrolysis of salts of iminophosphoranes
_-I. and III gave
high yields of secondary arylamines uncontaminated by the extraneous
products usually formed during direct alkylation of primary amines and
this method has been developed as a new synthetic route. Although the
relative rates of formation of salts from iminophosphoranes and alkyl
halides were found to be RI > Or > RC1, tertiary halides often underwent
elimination rather than substitution by the iminophosphoranes.
Whereas iminophosphoranes III and IV gave mono and bisalkylated
products, depending on the halide used, iminophosphoranes II were
alkylated on the pyridine ring only.
Novel complexes between iminophosphoranes I and II and Group VI
transition metal carbonyls have been prepared and their structures
elucidated. Their chemical reactions have been studied to discover
whether the reactivity of the free ligands is significantly modified,
to an extent useful in organic synthesis, by the transition metal atoms.
Electrophilic aromatic substitution reactions and oxidative coupling
studies of iminophosphoranes have been investigated to provide access
to substituted amines and biphenyls.