Phosphinines synthesis

The triple bond of phosphaalkynes also acts as a dienophile with phosphole sulfides, giving a cycloadduct (167) that readily loses the bridging phosphine sulfide group and is converted to a phosphinine derivative, (168) (Scheme 34) <86ZN(B)93l>. The reaction has practical value as a phosphinine synthesis. 

Interest in the synthesis and reactivity of the six-membered, potentially aromatic, phosphinine ring system has also continued, but at a much lower level than in recent years. New synthetic work includes the application of the pyrylium salt route to phosphinine synthesis, this time starting from pyrylium salts bearing chiral substituents to give the related chiral phosphinines," and the development of new routes to the 2-phosphanaphthalene (137)" ° and the phosphinine-2-aldehyde (138). Also reported is an approach to the synthesis of l,2-dihydro-l,4,2-benzo-diazaphosphinines," cationic gold(I) complexes of 2,4,6-tri-t-butyl-l,3,5-triphosphabenzene," and the synthesis of some X -phosphinines from phosphonium-iodonium ylides." " ... 

Example 63 Meier in his studies on potential prodrugs derived from biologically active nucleoside monophosphates used the cyclic chlorophosphites 2-chloro-4-ff-l,3,2,-benzodioxa-phosphinines for the synthesis of the cyclic phosphotriesters having two ligands of different hydrolytic stability benzy-loxy and aryloxy [102]. 

Scheme 3.12 Synthesis of Au NPs using phosphinine as capping ligand.

A convenient synthesis of phosphinines 185 involves the reaction of pyrylium salts 184 with either an excess of tris(trimethylsilyl)phosphine in acetonitrile, or alternatively with PH3 under pressure at 110°C <2001CEJ3106>. Better yields are often obtained using the direct reaction with PH3 (Equation 37). 2-t-Butyl phosphinines 187 can be prepared by reaction under pressure of /-butylphosphaacetylene with the a-pyrone 186 (Equation 38). 

Moores, A., Goettmann, F., Sanchez, C. and Le Floch, P. Phosphinine stabilized gold nanoparticles synthesis and immobilization on mesoporous materials, Chem. Commun. 2004, 2842-2843. 

Another facet of this versatile methodology is its potential for the synthesis of functionalized phospholes, which can be used for further chemical transformations. For example, anion 231, which was prepared by reduction with lithium of the corresponding P-chloro-phosphole and characterized by NMR spectroscopy, is an efficient intermediate for the preparation of functionalized phospholes 232 (66-80% yield) (Scheme 76) <1999OM4205>. These phospholes are useful precursors for the synthesis of mixed phosphinine- and phosphaferrocene-phosphole ligands. The l-(2-cyanoethyl)phosphole was characterized by an X-ray diffraction study <1999OM4205>. 

Routes to functionalised phosphinine systems, e.g., (202), and the phenolic systems (203) and (204), have been developed, the latter behaving as a genuine heterocyclic phenol. Whereas the 2-chlorophosphinine (205) is unreactive towards nucleophilic reagents, nucleophilic attack at phosphorus occurs in the related reactions of the P-W(C0)g complex of (205). The synthesis of the partially delocalised IX , 3X -diphosphabenzene system (206), and the 1X ,3X , 5X -triphosphabenzene system (207), has also been reported. Interest has also continued in the chemistry of azaphosphinine systems, although many of these involve phosphorus in the... 

Scheme 22. Synthesis of an enantiomerically pure functionalized phosphinine...

After the first synthesis of a P-phosphinin derivative, the 2,4,6-triphenyl compound (1) <66AG(E)846>, and the isolation of the unsubstituted phosphinin (2) <7UA3293>, a dramatic development and an avalanche of publications followed. 

An even longer chapter of six-membered phosphorus heterocycles with more than one heteroatom is represented by those with 2 (j -phosphorus. The first synthesis of a 2 -phosphinin, the 1,1-diphenyl compound (11) was described in 1963 <63AG(E)479>. Because of the ready availability of... 

Reduction of (317) with SiHCls and thermolysis at 200-250°C opens a useful route to the X -phosphinines (318) (R = H, Me R = Me, Bu , Ph, 4-MeC( H4, 4-CIQH4, a-furyl) (Scheme 62) <74TL4385,83CB445,83CB1756). The synthesis of 3-hydroxyphosphinines also starts from the phospha-enones (317) <77TL3445>. 

For several reasons the development of the chemistry of 6n heteroaromatic arsenic systems, for example arsinine (3), was much less vigorous than that of the phosphinines. While t-butylphos-phaethyne (4) and several other phosphaethynes are important building blocks for the synthesis of six-membered aromatic phosphorus heterocycles with more than one heteroatom, only one compound with a C=As triple bond, the 2,4,6-tri- -butylphenyl derivative (5), has been described <86AG(E)264>, and this has not been thoroughly studied. The only six-membered As-heteroaromatic system with more than one heteroatom is the l,3A -azarsinine (6) <88TL535>. Since pentavalent... 

Abstract Recent developments in the chemistry of phosphinines are reported. This chapter presents and discusses the most important breakthroughs achieved during the last decade. New synthetic approaches allowing the synthesis of polyfunctional phosphinines as well as improvements of well known methods are reported. The use of phosphinines in coordination chemistry is also presented with particular emphasis on their use in the stabilization of low valent and highly reduced transition metal complexes. Another aim of this review is to discuss recent applications of phosphinines, and structures derived directly from phosphinines such as phosphacyclohexadienyl anions and phosphabarrelenes, as ligands in homogeneous catalysis. 

The O + /P exchange from pyrilium salt using a source of PH3 is the classical procedure that allowed the synthesis of the first phosphinine, the ubiquitous 2,4,6-triphenylderivative 1 reported by Markl in 1966. This straightforward approach which relies on the use of easily available and inexpensive compounds... 

Most importantly, this O + /P exchange proved to be very appropriate for the synthesis of atropoisomeric phosphinines. Miiller and his group shown that phos-phinine 6 could be obtained as a 1 1 mixture of enantiomers and that separation could be successfully achieved by analytical HPLC (Fig. 2) [14], A rotational barrier of DG = 116 kJ mol 1 for enantiomerization of 6 was predicted by means of DFT calculations, indicating that 6 is expected to be configurationally stable at room temperature [15],... 

Noteworthy, 2-bromophosphinines have also found an interesting application in the synthesis of a new class of phosphinine-based bidentate ligands featuring either a phosphine or a phosphorus heterocycle like phosphirene or 1,2-dihydrophosphete. Reaction of phosphorus tribromide with 2-bromophosphinine 25 afforded the 2-dibromophosphinophosphinine 27 which in turn could be converted to functional derivatives either through nucleophilic or electrophilic reaction at the P-Br bonds. The mechanism of this phosphination process was shown to involve the transient formation of the A5-di bromophosphinine 26 (Scheme 7) [26],... 

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