Phosphorins disubstituted

Table 14. 1.1-Disubstituted X -phosphorins from X -phosphorins by diazonium salt oxidation...

One of the most versatile methods for the preparation of 1,1-disubstituted X -phosphorins 124 was discovered by Stade who found that X -phosphorins 2 can be oxidized (mercuric acetate gives the best results) in the presence of alcohols or phenols in benzene to 1.1-dialkoxy- or l.l-diphenoxy-X -phosphorins 124. The first step is probably a reaction of the soft X -phosphorin- jr-system with the soft acid Hg which by electron transfer leads to the weakly electrophilic radical cation 58. This is then attacked by alcohol or phenol - or as Hettche has found by other nucleophiles such as an amine to form by loss of a proton the neutral X -phosphorin radical 59. This radical is oxidized once again by mercury ions leading to the formation of elemental mercury and the strongly electrophilic, short-lived X -phosphorin cation 127, which is immediately attacked by alcohol, phenol or amine. Loss of a proton then leads to the X -phosphorin 124. It is also conceivable that 59 can couple directly with a radical to form 124 (Method E, p. 82). 

Only those 1.1-diphenyl-X -phosphorins in which the phosphorin ring is unsubstituted could be alkylated or acylated at the ring (see p. 77). The 2.4.6-tri-phenylated 1.1-disubstituted A -phosphorins cannot be alkylated by oxonium salts or acylated by acylchlorides under normal conditions. 

As mentioned on p. 90, Markl has found that compounds having the 1.2-dihydro-X -phosphorin structure 777 thermally rearrange to 1.1-disubstituted X -phosphorins 178. On prolonged heating 178 splits off the two benzyl groups and yields 2.4.6-triphenyl-X -phosphorin 22. This sequence corresponds to thermodynamic stabilities. 

Phosphorinanones have been utilized as substrates for the preparation of alkenes,11 amines,12 indoles,5,13 and in the synthesis of a series of secondary and tertiary alcohols via reduction,10 and by reaction with Grignard6,11 and Refor-matsky11,14 reagents. Phosphorinanones have also been used as precursors to a series of 1,4-disubstituted phosphorins.15 The use of 4-amino-l,2,5,6-tetrahydro-l-phenylphosphorin-3-carbonitrile for the direct formation of phosphorino-[4,3-d] pyrimidines has been reported.16... 

Wang and Schleyer have investigated various 1,1-disubstituted-phosphorins 9 and arsenins 10 at the B3LYP/6-31G DFT level <2001HCA1578>. Based on the NICS(l) values, they find that the compounds are nonaromatic ylides (resonance structures 9 and 10 dominant) for electropositive substituents. However, for electronegative substituents, the compounds are aromatic. 

A niimber of 3,5-disubstituted and 3,4,5-trisubstituted X --phosphorins have been prepared from 1,2,3,6-tetrahydro-1- te2 t butylphosphorin-3-ones (Markl, Hock, and L. Merz, Ber., 1984, JM7, 763). 

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