Diazaphospholidine oxides

Aromatic isocyanates, particularly those containing electron-attracting substituents, react noticeably more easily than aliphatic isocyanates. In the former case it often suffices to leave the components for some hours at room temperature in a water-pump vacuum, whereas for aliphatic compounds boiling under reflux is usually necessary and sometimes use of a higher-boiling solvent such as decalin. The best catalysts are cyclic phosphine oxides of type (1) (phospholene oxides)862 and cyclic phosphonic diamides of type (2) (1,3,2-diazaphospholidine oxides).863 The best results were obtained with compound (1, R = C2H5) (for its preparation see Campbell et a/.862) the phenyl compound, although more readily prepared,864 is somewhat less reactive. The amounts of catalyst needed are 0.1% for (1) or 0.5% for (2). 

To avoid one step, the phosphine oxide version of route A (Scheme 3.1) has also been explored for the direct preparation of diazaphospholidine oxides (7) from P(V) precursors (Scheme 3.5 and Table 3.5). 

Buono and co-workers showed that (aryloxy)diazaphospholidine oxides suffer [1,3] P-O to P-C rearrangement, i.e. migration of the phosphine moiety from the oxygen to the ortho carbon upon treatment with strong bases such as LDA. For instance, treatment of compound 12 with LDA followed by an aqueous work-up allowed the isolation of the o-hydroxyphenyl diazaphospholidine oxide 13 in 94% yield (Scheme 3.6). ... 

The diazaphospholidine oxide group activates the ortho position towards metallation (Scheme 3.7) creating the stabilised carbanion 14, which intramo-lecularly attacks the phosphorus atom producing the product 13. It has been suggested that the driving force of the reaction is the extra stabilisation of the lithium cation by two oxygen atoms in 13 compared to only one in 12. ... 

The high yields and the flawless stereoselectivity of this rearrangement prompted the preparation of several o-hydroxyaryl diazaphospholidine oxides. 

This class of compounds is interesting because of its bifunctional character, displaying both an acidic OH and a basic phosphoryl group. Table 3.7 lists the o-hydroxy diazaphospholidine oxides prepared via P-0 to P-C rearrangement. 

Scheme 3.5 Synthesis of diazaphospholidine oxides from P(V) precursors.

Table 3.5 Diazaphospholidine oxides prepared by direct condensation of 10 with (iS)-5.

Table 3.6 Diazaphospholidine oxides prepared from precursor 11.

Monodentate Phosphinites, Aminophosphinites, Diazaphospholidines and Secondary Phosphine Oxides... 

Scheme 28.13 Monodentate phosphinites, aminophosphinites, diazaphospholidines and secondary phosphine oxides.

Catalytic conversion of isocyanates into carbodiimides with the aid of l,3-dimethyl-l,3,2-diazaphospholidine 2-oxides and 1,3-dimethylhexahydro-1,3,2-diazaphosphorine 2-oxides [79]. 

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. ... 

Wyatt, P.B., Villalonga-Barber, C., and Molevalli, M., Synthesis and Diels-Alder reactivity of chiral 2-(alk-l-cnyl) 1,3,2-diazaphospholidine 2-oxides, Tetrahedron Lett., 40. 149. 1999. 

The addition of acyl hydrazides to (l,2-alkadiene)phosphonic diamides (325) yields the 1,2,3-diazaphospholidine 3-oxides (326). Interaction of the phospho-nite esters (327) (X = Cl or Br) with a,P-unsaturated carboxylic esters, nitriles, ketones, or related compounds, gives quaternary products which decompose in boiling benzene to produce the dihydrophospholes (328). ... 

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. 

Isopropylidenedioxy-substituted BCOD-fused pyrrole 52d was deprotected to afford the dihydroxy derivative, which was transformed via cyclic thiocarbonate by treatment with thiocarbonyldiimidazole to bicyclo[2.2.2]octatriene-fused (BCOT-ftised) pyrrole 54 by l,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine [57]. Quadmply BCOT-fused porphyrin 55 was obtained in 66% yield by the usual cyclic tetramerization method [58]. In this reaction, an interesting by-product, triply BCOT-fused porphyrin, was obtained in a very small amount. This by-product was thought to be formed by the rDA reaction of intermediates during the oxidation of porphyrinogen to porphyrin [59]. 

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