Phosphorin derivatives

Another interesting rearrangement has been reported by Paddock and CO workers [171,172]. The reaction of sodium bis(trimethylsilyl)amide with A-methyl phosphazenium iodides N P Me2 +iI (n = 3, 4) gives the corresponding phosphorin derivatives (Eq. 30) via deprotonation and rearrangement. The crystal structure of the rearranged trimer derivative has been published [173]. 

The IR spectra of the corresponding benzene, pyridine and X -phosphorin derivatives resemble each other, although X -phosphorin is spectrally closer to benzene than to pyridine. Only in the region 1200—1400 cm additional bands are to be detected. However, these alone do not suffice to identify the X -phosphorin system. Fig. 8 shows the IR spectra of 2.4.6-tri-tert-butyl-X -phosphorin compared with those of the anologous benzene and pyridine derivatives. 

Transformation of X -phosphorins to other X -phosphorin-derivatives. Methods 2) and 3) allow for the highest degree of synthetic variation. X -Phos-... 

Finally, we point to the possibility of P = 0 bond formation from 1-alkoxy-X -phosphorin derivatives 124 or 125 by cleavage of alkyl cations. Also the reverse process, /. e. alkylation of the P = O moiety to form P—O—R groups is possible. The synthesis of X -phosphorins having functional groups at the C-atoms of the phosphorin ring was first made possible by the preparation of new stable X -phosphorin carbenium ions 140. Here again, the fundamental difference between phosphorin and pyridine systems comes to light Whereas carbanionic structures 139 b are stabilized in the pyridine series, in the X -phosphorin series carbenium ions as 140 b are stabilized. 

Markl, Lieb and Merz have described the carbanionic addition of lithium or magnesium organometallic compounds to the P atom of 2.4.6-triphenyl-X -phos-phorins, which form deep red s ts 143. These can be alkylated either at the P atom to form X -phosphorins 144 or at C—2 to yield 1,2-dihydro-X -phosphorins 145. Acylation with benzoylchloride affords the 1,4-dihydro-X -phosphorin derivatives 146. Addition of acids or water leads to the synthetically important intermediates 147 which can be reconverted to the X -phosphorin-salts 143 by 2 N NaOH. 

If the radical reactions (Method E) with triphenylphenoxyl or diphenylaminyl are carried out in the presence of an excess of alcohols, one obtains the mixed 1,1-sub-stituted X -phosphorin derivatives with either phenoxy or diaiylamino and one... 

X -phosphorins have physical properties which are rather similar to those of pyridines. But the chemistry of X -phosphorins is very different, due mainly to the phosphorus atom which can easily lose one electron to produce a stable radical cation, or accept one or more electrons to yield a radical anion, dianion or radical trianion. Nucleophiles add to stable X -phosphorin anions. In contrast to pyridine chemistry, no stable X -phosphorinium compound (corresponding to a N-alkyl-pyridinium salt) could be isolated. Instead the electron shell of phosphorus is enlarged by addition of an electrophile yielding a X -phosphorine derivative. 

Similarly, the mass spectra of the tri-O-acetyl derivative (127) of 3,6-di-0-benzyl-5-(phenylphosphinyl)-D-glucopyranose and of those (19 and 20) of 5-(methoxyphosphinyl)xylopyranose have been analyzed81 the main fragmentation is, again, the stepwise removal of the substituents from the ring-carbon atoms and C-6 (series A), leading to the formation of similar l,2-dihydro-A5-phosphorine derivatives. 

A 3-Phosphorin derivatives of benzo annelated rings were intensively studied by Bickel-haupt and coworkers. One of his preferred methods consists in the introduction of the final P=C double bond from appropriate ring systems by basic elimination of HC1 with DBU or other bases. Many benzo-A 3- phosphorins have been reported. An example is the synthesis of 2-phosphanaphthalene (equation 26) (75T1097). Some other examples are shown in (32)-(35). 

X-ray analyses of two rather different substituted A3-phosphorin derivatives, 2,6-dimethyl-4-phenyl-A3-phosphorin (36) and the compound (37) were carried out by two different authors at the same time, giving nearly identical results (68AG(E)81l, 68TL6227). The A3-phosphorin ring is planar, P—C distances are 1.734 and 1.746, and 1.75 and 1.75 A, respectively, and the C—P—C angles are 102.9° and 103°, respectively. 

Three different methods exist for the synthesis of As-phosphorin derivatives from A3-phosphorins. 

Very useful transformations of the 4 -methylcarbenium salts (49) are possible in the presence of electrophiles and trace amounts of water. The 4-CH2+ group first gives the unstable 4-CH2OH derivatives (62), which with electrophiles, e.g. the carbenium salts (49) themselves or aryldiazonium salts, give the 4-E substituted A -phosphorin derivatives (63) or (64), respectively. The CH2OH+ group leaves position 4, and stable 4-E substituted A5-phosphorins are formed (equation (36)) (72TL843). 

The ylid character of X5-phosphorins and their Cr(C0)3 complexes again is evident when one or both groups on phosphorus are CHR2 as one can abstract a+ protpn giving a carbanion. Reaction with electrophiles (e.g. D, CH3, and RCHO) causes side chain addition. No Wittig olefination is found with aldehydes. Instead a 1(2 -hydroxy) product 9 is formed which can be dehydrated to the X5-phosphorin derivative 10. 

When cation-radicals from A3-phosphorins such as 188 are formed in the presence of nucleophiles and excess of oxidant, further reaction takes place to give A5-phosphorin derivatives, e.g., 191, generated in the presence of methanol by oxidation of 188 with mercuric acetate.611-614 A crystal and molecular structure determination of a A5-phosphorin shows a planar heterocycle with spd-hybridized phosphorus.615 Anion- and cation-radicals are also obtainable from the A5-phosphorin system.606,611,612... 

Also reported are radicals formed by the oxidation of X -phosphorin derivatives Cdem ibid, p.3004). 

Studies or reports have been made of - the temporary anion states of phosphorin, arsabenzene, and stibabenzene (P.D. Burrow et at, J- Amer. chem. Soc., 1982, 104, 425) the anomalously low basicity of phosphorin and arsabenzene (Ashe et at, ibid, 1979, 101, 1764) the ir and Raman spectra of phosphorin and arsabenzene (Ashe, G.L. Jones, and F.A. Miller, J. mol. Struct., 1982, 78. 169) the photochemical rearrangements of 1-acyloxy-1-alkoxy-X -phosphorin derivatives (M. Constenla and Dimroth, Ber., 1976, 109, 3099) the angular and energy dependence of band intensities in the photoelectron spectra of phosphorin and arsabenzene (Ashe et at, Helv., 1976, 1944) calculations of spin-orbital... 

Among the typically organic heterocycles of Fig. 1, the 1-methylphos-phole 12) 1 does not necessarily contribute dn orbitals to the rr-system besides its p lone pair13). The same holds for the phosphabenzene derivatives 2a 14> and 2b 1ST But in the phosphorine derivatives 3a 16>, 3b l7>, 3c 18> and 3d 19>, as well as in 1,1,3,3-tetraphenyl-l,3-diphosphabenzene 2°) 4 and 1-phenyl-1 H-phosphepine-l-oxide 21> 5 which contain tetrahedral phosphorous atoms, cyclic conjugation can only be achieved by the use of outer d orbitals. The resultant bonding situation has been treated theoretically by Mason 22> using HMO theory. 

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