Phosphinylation

The Mpt and Ppt derivatives can be prepared from an amino acid and the thio-phosphinyl chloride (Me2PSCl or Ph2PSCl, respectively, 41-78% yield, lysine gives 16% yield)." The Mpt group is cleaved with HCl or Ph P- HCl and is cleaved 60 times faster than the BOC group. The Ppt group is the more stable of the two groups. 

Scheme 2.7 Stereoselective aziridination of N-diphenyl-phosphinyl aldimines 19.

The acyl phosphonates, acyl phosphine oxides and related compounds (e.g. 81. 82) absorb strongly in the near UV (350-400 nm) and generally decompose by rescission in a manner analogous to the benzoin derivatives.381"285 Quantum yields vary from 0.3 to 1.0 depending on structure. The phosphinyl radicals are highly reactive towards unsaturated substrates and appear to have a high specificity for addition v.v abstraction (see 3.4.3.2). 

Phosphinyl radicals (e.g. 103-107) arc generated by photodecomposition of acyl phosphinates or acyl phosphine oxides (see 3.3.4.LI)282,466 474,473 or by hydrogen abstraction from the appropriate phosphine oxide.467... 

The reactivities of the various phosphinyl radicals with monomers have been examined (Table 3. lO).283-465,467-475 Absolute rate constants are high, lying in the range 106-I08 M 1 s 1 and show some solvent dependence. The rate constants are higher in aqueous acetonitrile solvent than in methanol. The high magnitude of the rate constants has been linked to the pyramidal structure of the phosphinyl radicals.46- ... 

The phosphinyl radicals (103-107) all show nucleophilic character (eg. VAc is substantially less reactive than the acrylic monomers). However, the... 

Bromomethyl-6,7-dimethyl-3-phenylquinoxaline (286) gave 2-(dimethoxy-phosphinyl)methyl-6,7-dimethyl-3-phenylquinoxaline (287) [P(OMe)3, PhMe, reflux, 5h 45%]. ... 

CN [1 [5 (R )],2a,4p]-4-cyclohexyl-1 -[[[2-methyl-1-( 1 -oxopropoxy)propoxy](4-phenylbutyl)phosphinyl]acetyl]-L-proline... 

C20H2JNO3 3608-67-/) see Propiverine (-)-(lS,2S)-/V-(2-hydroxy-l-phenyl-3-butenyl)benzamide (C17H17NO2 136693-02-2) see Paclitaxel [hydroxy(4-phenylbutyl)phosphinyl]acetic acid phenylmc-thyl ester... 

An a-fluorinated phosphinyl sulfoxide derivative, prepared as a mixture of diastereomers by the treatment of lithiated (a-fluoromethyl)diphenylphosphine oxide with menthyl p-toluenesulfinate, has been used for the preparation of enan-tiomerically pure 1-fluorovinyl and 1-fluoromethyl sulfoxides [76]. (E)-Diethyl ferf-butylsulfinylmethylphosphonate 117 has been prepared by the sulfinylation... 

This chapter surveys the literature published from 1995 to 2003, concerning the reactivity and the chemical applications of the four main families of phosphorus centered radicals, i.e., phosphinyl (L2P )> phosphonyl (L2P =0), phospho-niumyl (L3P ) and related charged species, and phosphoranyl (L4P ) radicals. Due to their specificity, a section is devoted to the generation and properties of persistent and stable phosphorus centered radicals. 

Although their chemistry is less developed than that of phosphonyl, phospho-niumyl or phosphoranyl radicals, many structural studies have been devoted to phosphinyl radicals [1]. Like their nitrogen analogs,phosphinyl radicals are 7i-type radicals (Fig. 1) and because of the very small s character of their SOMO, the magnitude of their phosphorus hyperfine coupling constants flp is below 15 mT [1]. 

Due to their weak P-H bonds (-370 kj mol"0 [2] and the high rate constants for the transfer of the P-H hydrogen [3] (/c=1.5 10 L rnoL s" for Ph2PH and k=5,0 10 L mol s for (c-hexyl)2PH), diaryl and dialkyl phosphines present a high interest as H-donors. Since the corresponding phosphinyl radicals are good chain carriers [4,5], diaryl and dialkyl phosphines can be added to olefinic or acetylenic compounds through radical chain reactions. Simpkins et al. [6] used... 

Scheme 1 5-exo Cyclization initiated by phosphinyl radical addition onto an alkyne... 

The first p-phosphaquinone radical anion (Fig. 8), another example of stable phosphinyl, was prepared by Yoshifuji et al. in 1998 [85]. 

In this context, the treatment of the AT-phosphinyl iminoethers 15 with methyl iodide furnish the P-methyl phosphonium iodides, which by heating experience an 0-dealkylation, reminiscent of the Arbuzov reaction, for yielding the iV-acylphosphazenes 16 [45] (Scheme 16). 

We have investigated the reaction of NH phosphinous amides with diphenyl-cyclopropanone. The products were unequivocally identified as the corresponding p-phosphinyl carboxamides 27 resulting from the hydrolysis of a presumed heterocyclic intermediate (Scheme 28) These results await publication. 

In 2004, Bolm et al. reported the use of chiral iridium complexes with chelating phosphinyl-imidazolylidene ligands in asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee [17]. These complexes were synthesized from the planar chiral [2.2]paracyclophane-based imida-zolium salts 74a-c with an imidazolylidenyl and a diphenylphosphino substituent in pseudo ortho positions of the [2.2]paracyclophane (Scheme 48). Treatment of 74a-c with t-BuOLi or t-BuOK in THF and subsequent reaction of the in situ formed carbenes with [Ir(cod)Cl]2 followed by anion exchange with NaBARF afforded complexes (Rp)-75a-c in 54-91% yield. The chela-... 

Grignard reactions have been used in the preparation of l-(dialkyl-phosphinyl)- ,3-dienes, e.g. (11), which are intermediates in the synthesis of antiflame polymers. Double-resonance n.m.r. techniques have been applied to the study of the reactions between thiophosphoryl halides and Grignard reagents. For example, the reaction between methylmag-nesium iodide and t-butyldibromophosphine sulphide gave the mixed... 

Deamination reactions of (2-amino-l,l-dimethyl)ethyldiphenylphosphine oxide (57) result in the formation of three products, in each of which the diphenylphosphinyl group has migrated to the primary carbon of the starting material. These reactions are unusual examples of non-assisted migration of a phosphinyl group. 

Phosphinyl radicals, obtained by hydrogen abstraction from dialkyl phosphites, have been trapped with t-nitrosobutane and the resultant nitroxyl radicals examined by e.s.r, The reaction of phosphinyl radicals, e.g. (5) and (6), with olefins has been shown to occur with retention of configuration at phosphorus. " These radicals have also been postulated as intermediates in the reactions of dialkyl disulphides and diaryl disulphides with phosphinates. " From the reaction of diphenyl disulphide... 

Sometimes it may become necessary to change the solvent. An example of phosphinyl acetic acid may be cited where crystallization from the aqueous phase did not provide a rugged process, whereas the use of methyl wo-butyl ketone (MIBK) as a solvent did. 

Palladium-catalysed asymmetrie allylations of various carbonyl compounds have been studied by Hiroi et al. using various types of chiral sulfonamides derived from a-amino acids. In particular, the chiral bidentate phosphinyl sulfonamide derived from (5)-proline and depicted in Scheme 1.63 was employed in the presence of palladium to eatalyse the allylation of methyl aminoacetate diphenyl ketimine with allyl aeetate, leading to the eorresponding (7 )-product with a moderate enantioseleetivity of 62% ee. This ligand was also applied to the allylation of a series of other nueleophiles, as shown in Seheme 1.63, providing the eorresponding allylated produets in moderate enantioseleetivities. 

Scheme 1.63 Test reaction with (5)-proline-derived phosphinyl sulfonamide ligand.

Scheme 1.77 Test reaction with l-phosphinyl-l -sulfinylferrocene ligands.

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