Phosphinoyl radical

Malacria and coworkers reported a vinylation sequence of epoxides by employing vinyl phosphine oxides as a radical trap. The overall sequence relies on the facile elimination of phosphinoyl radicals. With vinyl phosphonates the THF derivatives were obtained (Scheme 22). The reaction works equally well under stoichiometric or catalytic conditions [102,103],... 

The observed spectra (Fig. 12.7) consist mainly of polarized signals of spin adducts of a phosphinoyl radical and an acrylate with the following stmcture Scheme 12.6 demonstrates the so-called tail adduct, where r adds to a CH2 group ( tail ). Tail adducts are the most common in addition to substituted olefins. In this work, only the tail addition was observed. ... 

SCHEME 12.6 The stmcture of the main product of the addition of a phosphinoyl radical to IBOA... 

Substituted) benzoyl radicals are known to be much less reactive than phosphinoyl radicals in addition to acrylates, and benzoyl radicals persist contributing to the center of the CW experimental spectra of spin adducts (Fig. 12.7) see Table 12.2 and additional comments below. 

We conclude that the dominant process under photoinitiation of polymerization of (meth)acrylates by TPO (Scheme 12.1) is a tail addition of phosphinoyl radical to a double bond (Scheme 12.8). 

SCHEME 12.8 Reaction of a phosphinoyl radical with an acrylate. 

TR ESR allows not only structural identification of short-lived radicals but also provides insights into their conformation. Analysis of the ESR spectra of adducts of phosphinoyl radicals to acrylates reveals that these secondary radicals have two conformations (Scheme 12.11) ... 

FIGURE 12.12 Transient absorption spectrum obtained under laser flash photolysis of BAPO in acetonitrile. The spectrum is ascribed to a phosphinoyl radical. ... 

Fig. 12.13). In this case, the IR detection of transients can be a useful alternative. Substituted benzoyl, substituted benzyl and phosphinoyl radicals, often discussed in this chapter, have weak absorption in the UV region. On the contrary, benzoyl radicals have strong absorption in the mid-IR region in the 1780-1880 cm due to >C=0 vibrations. IR detection of transients is observed by using a diode laser fitted with monochromators and a sample chamber with a fast IR detector. TR IR spectra of several r are presented in Fig. 12.15. 

Scheme 31 Intramolecular radical vinylation based on the /3-phosphinoyl radical elimination...

En route to the synthesis of modified ohgonucleotides through radical addition of hypophosphorous substrate 177 to sugar 178, Hubert et al. reported the unforeseen /1-ehmination of a phosphinoyl radical from a phosphinate (Scheme 58) [167]. This example came after a 1,5-H translocation giving a more stabilized oj-oxy radical (from 179), and it demonstrates further that j6-phosphinoyl radicals are prone to undergo elimination (see Scheme 31), even when the substituents are all alkyl groups. 

Cp2TiCl-mediated intramolecular radical vinylations based on the elimination of P-phosphinoyl radicals have recently been reported by Leca... 

H-CIDNP and ESR techniques. A laser flash photolysis and time-resolved ESR study of the formation of phosphinoyl radicals from benzoyldiphenyl-phosphine oxide and 257 has appeared. The addition of dialkyIphosphoryl radicals to a fullerene system has also been studied. Interest in adducts of phosphine oxides with proton donors, notably phenols and other solvent guests ° has continued. 

It is interesting that hydrogen abstraction to form phosphonyl radicals is comparable to that of phenyl-substituted silanes (1.2 x 105 M s )4 On the other hand, Turro and Jockusch showed that phosphinoyl radicals [R2P(0) ] are... 

Phosphinoyl radicals are much more reactive towards olefinic compounds than carbon-centered radicals. For example, the rate constants for the addition of diphenylphosphinoyl radicals (see Scheme 10.2) to vinyl monomers are of the order 10 to 10 m s , i.e. one or two orders of magnitude larger than those... 

The titanium-mediated intramolecular radical vinylations of oxirane was first reported to yield alkylidene pyrrolidines 488 via the radical (3-elimination of phosphinoyl radical. The reactions of phosphine oxide precursors 487 with a stoichiometric amount of Cp2TiQ2 were carried out at room temperature using powdered manganese as reductant, from which pyrrolidines 488 were obtained in 57-82% yields (Scheme 4.146). The procedure for the synthesis of phosphine oxide precursors 487 is also shown in Scheme 4.146. 

SLU 96] Sluggett G.W., Mcgarry P.F., Koptyug I.V. et al, Laser flash photolysis and time-resolved esr study of phosphinoyl radical structure and... 

Figure 4.5. Reaction scheme for the formation ofstarting radicals from TPO a) a-cleavage of the C-P bondforming C-centered acyl and P-centered phosphinoyl radicals and b) possible H-atom abstraction and radical shift from the C-centered acyl radical [NEU 06]...

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