Rearrangement phosphorins

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]. 

CH2) rearrange at 180—220° to the 1,1-compounds 144. At hi er temperatures these substituents are split off, forming 2.4.6-triphenyl-X -phosphorin 22. Attempts to convert 2.4.6-tri-tert-butyt-X -phosphorin to l,l-dimethyl-2.4.6-tri-... 

Whereas related rearrangements involving hydrogen migration have been observed in the transformation of cyclo-X -phosphazadienes 179 to cyclo-X -phosphaza-trienes 180 (Schmidpeter and Ebeling ), no such processes have been observed for 1,2-dihydro-X -phosphorins, i. e. 181 fails to rearrange io 182. 

Trisubstituted X -phosphorins or X -phosphorins can be isolated unchanged even after long periods of irradiation when oxygen is excluded. Stade discovered that cyclic phosphinic acid esters 208 a-c which contain a cyclic butadiene (1.3)-moiety, photochemically rearrange smoothly to the tricyclic compounds 214 a-c. 

Dialkoxy-X -phosphorins (90 a, R and H = alkyl) at temperatures such as 200 °C do not rearrange, but at higher temperatures a similar rearrangement cannot be excluded. 

The results are consistent with a [1.7] sigmatropic COCH3 rearrangement it is [1,7] and not [1.3] because the delocalized tt bonds in X -phosphorin must be taken into account. 

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. 

Another synthesis recently reported by Markl (81LA870) involves rearrangement of l-R-4-R1-4-methoxy-l,4-dihydrophosphorins (cis and trans isomers) under acid conditions. The method gives rise to many 2,6-unsubstituted A5-phosphorins (equation (31)). 

Substituted 4-alkyl- and 4-phenyl-1,4-dihydro-4--methoxy-X" -phosphorin (2) are obtained by cyclization of the dilithium compound (1) with the appropriate substituted phosphorus dichloride. The acid-catalysed rearrangement of (2) yields the 1,4-substituted 4-methoxy-A -phosphorin (3), which on acid-catalysed hydrolysis affords the 1-oxide (4) and on oxidative methylation the 4-substituted 1,1-dimethoxy-A --phosphorin (5) (G. Markl et al., Ann., 1981, 870). 

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... 

Phosphorylation of 203 by using 2-methylthio-4//-l,3,2-benzodioxa-phosphorin-2-oxide (MTBO) in the presence of 4-morpholine-/V, iV-dicyclohexylcarboxamidine as a catalyst gave 204 that rearranged to 205 (86MI3 91ABC1999) (Scheme 65). 

The conversion of (298) into (300) upon gas-phase thermolysis occurs by a Cope rearrangement and not by a [1,3] carbon shift or a bisallyl radical mechanism. Thus, similar treatment of (299) affords only (301). Rearrangement of 3-oxobicyclo-[3,2,l]oct-6-ene to 3-oxobicyclo[3,3,0]oct-6-ene occurs only at much higher temperature and presumably by way of a non-concerted mechanism. The nickel-catalysed reaction of norbornene with butadiene affords the 1 2 cxo-adduct (302) which upon thermolysis is converted into the valence isomer (303). Concerted and non-concerted Claisen-type rearrangements have been observed in the A, -phosphorin series. Tricyclo[7,3,0,0 ]dodeca-2,5,7,10-tetraene (304), which is available in six steps starting from bicyclo[3,3,0]octa-3,7-dien-2,6-dione, appears to be an essentially static structure (as assessed by n.m.r. spectroscopy) up to 141 The slow... 

---