Laser flash photolysis evidence for styryl radical cation cyclization in the SET-induced photorearrangement of a p-methoxy-substituted 2-phenylallyl phosphite

The SET-induced photorearrangement of dimethyl 2-(4-methoxyphenyl)allyl phosphite, 9 (UV light, uranium glass filter, 9,10-dicyanoanthracene (DCA), biphenyl), gives phosphonate 12 in 83% isolated yield. Laser flash irradiation at 355 nm of oxygen saturated solutions of phosphite 9 containing DCA and biphenyl generates the transient UV spectrum of the biphenyl radical cation that is quenched by electron transfer from phosphite 9 (k(q) = 8.9 x 10(9) M(-1) s(-1) at 20 degrees C) to form the 4-methoxystyryl cation 10. The UV spectrum of 10 decays by a measured first-order rate constant of 8.0 x 10(6) s(-1), presumably to generate the cyclic distonic radical cation 11. Intermediate 10 was further characterized by measurement of the second-order rate constants for its reaction with azide, chloride, and bromide ions and with the neutral nucleophile trimethyl phosphite. This study provides the first spectroscopic evidence regarding the proposed mechanism (Schemes 1 and 2) for the SET-induced photorearrangements of dimethyl 2-arylallyl phosphites to the corresponding 2-arylallylphosphonates. Moreover, absolute rate constants for the intramolecular trapping of alkene radical cations have seldom been measured. The removal of the electron from the styryl moiety of phosphite 9, rather than from phosphorus, and the detectability of 10 arise from the stabilizing effect of the 4-methoxy substituent. These results, however, do not allow conclusions to be made concerning the site of removal of an electron in the SET-induced photorearrangement of dimethyl 2-phenylallyl phosphite 1 to phosphonate 6.     

Stereochemistry of substitution at tricovalent phosphorus

Reactions of one diasteveomer of a XP-NMe₂ compound ($\text{1a}$) with alcohols, phenol and amines have been shown by NMR to proceed uith initial inversion at phosphorus, but the overall reactions are not stereoselective.     

Nonaqueous oxidation of phosphites to phosphates in nucleotide synthesis

$\text{m}$-Chloroperbenzoic acid in methylene chloride represents a rapid non-aqueous method for the conversion of phosphites to phosphates during oligonucleotide synthesis both in solution and on a solid support.     

Stereochemistry of 1-hydroxyphosphonate-phosphate rearrangement. Retention of configuration at the phosphorus atom

1-Hydroxyphosphonate 1 in the presence of triethylamine in acetonitrile solution undergoes irreversible rearrangement to phosphate 2 and reversible retro-phospho-aldol (retro-Abramov) reaction. The X-ray structures for 1 and 2 revealed that the phosphonate-phosphate rearrangement occurs with retention of configuration at the phosphorus atom.     

The mass spectra of phosphorus esters. I. Bicyclic phosphites

The mass spectra of bicyclic phosphites of the type P(OCH₂)₃CR, where R = CH₃, C₂H₅, and C₃H₇ and NO₂, are reported, and their fragmentation patterns analyzed. Unlike trialkyl phosphites, these cyclic phosphites do not yield a large number of phosphorus-containing fragment ions resulting from hydrogen rearrangement.     

Stereochemistry of the addition of dialkyl phosphites to (S)-N,N-dibenzylphenylglycinal

The addition of various dialkyl phosphite derivatives to (S)-N,N-dibenzylphenylglycinal 6 led to the preponderance of anti over syn diastereoisomers: from 75:25 when NEt₃ or Ti(OiPr)₄ were used to 51:49 for Li or Mg salts. In the NEt₃-catalysed reaction, partially racemised phosphonates were formed, while enantiomeric products were obtained after addition of lithium O,O-dimethylphosphonate to (S)-6 at −70°C. Because the syn-isomers were found to be resistant to O-benzoylation, mixtures of diastereoisomers were easily separated after esterification of the anti products. Hydrogenation of the syn-phosphonates in the presence of Boc₂O gave enantiomeric dialkyl N-Boc-2-amino-1-hydroxy-2-phenylethylphosphonates—phosphonate analogues of the docetaxel C-13 side chain.     

Acid-base properties of phosphorus compounds 12. Stereochemistry of H-bonded complexes of phosphorus compounds

Conclusions Measurements of the dipole moments of R₃P = O... HOR' type complexes with weak H-bonding (_H0) have shown that the angle of coordination of the phosphoryl group at the H-bond to be 109 ± 6°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1531–1534, July, 1977.     

Energy barrier in the photorearrangement of azoxybenzene to 2-hydroxyazobenzene

The temperature dependence of the quantum yields of the photorearrangement of azoxybenzene in polar protic solvents and of 6,2′-dimethylazoxybenzene in polar protic and non-polar solvents to the corresponding 2-hydroxyazobenzenes in the range from room temperature to liquid nitrogen temperature was studied. It is shown that an energy barrier exists in the path from the ground state intermediate, observed in this work for the first time, to the photoproduct. The formation of the ground state intermediate also appears to be temperature dependent. Further, the observation that the quantum yields of the photorearrangement of 6,2′-dimethylazoxybenzene in non-polar and polar protic solvents at room temperature are comparable indicates that it is not catalysed solely by the presence of proton-donating solvents.     

Stereochemistry of cyclic compounds Communication 62. Stereochemistry of the oxidation of 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride

Summary The stereochemistry of the oxidation of 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride with peroxyacetic acid was studied, and by a series of transformations it was proved that the epoxide then formed has the ßconfiguration. The observed stereospecificity of the oxidation is explained on the basis of views on a predominant boat conformation for 4-cyclohexane-1,2-dicarboxylic anhydrides.This article is published in accordance with a resolution of the Conference of Chief Editors of the Journals of the Academy of Sciences of the USSR, July 12, 1962, as a dissertation paper by A. L. Shabanov.