Diazaphospholidine boranes

This methodology was applied successfully also for the diastereoselective synthesis of a series of P-stereogenic (o-hydroxyaryl)diazaphospholidine - borane complexes 250-257 (yields ranging from 40 to 86%) via the reaction sequence shown in Scheme 61 with a one-pot formation of the appropriate (o-bromoaryloxy) diazaphospholidine-borane complexes 242-249 in yields ranging from 70 to 92% (Scheme 61) [93],... 

New P-stereogenic (o-hydroxyaryl)diazaphospholidines, in the form of their borane complexes (19), have been synthesized in a totally diastereoselective manner by a P-0 to P-C migration rearrangement of (o-bromoaryloxy)diazaphospholidine-borane complexes (18) mediated by r-BuLi (Scheme 5).16 The stereoselective rearrangement, confirmed by X-ray diffraction study of the structures of the product (21) and its precursor (20), occurs with clean retention of the phosphorus configuration. 

Diazaphospholidines have been successfully applied as ligands in several transition metal-catalysed reactions. In addition, some have been subjected to further transformations (Scheme 3.4) to yield diazaphospholidine boranes 6 and some P(V) compounds oxides 7, sulfides 8 and iminophosphines 9. Most of the reactions have been found to proceed with complete retention of configuration at the phosphorus atom. 

The reaction has been extended to diazaphospholidine boranes (Scheme 3.10). In this case, the presence of bromine in the ortho position is needed to allow the formation of the carbanion, which subsequently attacks the phosphorus centre. In addition, the reaction was found to be completely stereoselective, once more with retention of configuration at the phosphorus atom. It has to be mentioned that the reaction does not work for unprotected diazaphospholidines. 

Complexation of the latter at phosphorus with borane, followed by methanolysis of the siloxyether function, gives the related o-hydroxyaryl diazaphospholidines. The cage-like triaminophosphine (109) has been obtained from the reaction of tri(2-pyrrolyl)methane with phosphorus trichloride, in the presence of triethylamine. This compound is stable to methanolysis, hydrolysis, and aerial oxidation at room temperature. Phosphorylation of various 1,2,4-triazoles with halophosphines has given a route to the heterocyclic system (110), and routes to various [2,4,l]benzodiazaphosphinines, e.g., (Ill), have also been developed. ... 

X-ray diffraction analysis of the borane adduct of 2 (R = Ar = Ph, Scheme 3.1) revealed the P-bonded extracyclic phenyl group to be in the traits position to the pyrrolidine ring, forcing the phosphorus atom to adopt R as the absolute configuration in order to minimise steric effects. Most of the diazaphospholidines prepared by route B are listed in Table 3.2. 

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