A Convenient Synthesis of Phosphonic Anhydrides − Trimers [RPO2]3 (R = tert-Butyl, 2-Methylphenyl, 2,4,6-Trimethylphenyl): Their Structures and Reaction Products
✍ Scribed by Klaus Diemert; Wilhelm Kuchen; Wolfgang Poll; Frank Sandt
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 458 KB
- Volume
- 1998
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
By reaction of RP(O)Cl 2 with RP(O)(OSiMe 3 ) 2 , phosphonic with N-benzyloxycarbonylglycine (4) in methanol affords strong evidence that in the first step of peptide synthesis with anhydrides (RPO 2 ) 3 (R = tBu, 2-methylphenyl, 2,4,6-trimethylphenyl) 1a؊c are conveniently obtained. In contrast to 1b (RPO 2 ) 3 , a mixed anhydride of triphosphonic acid and the Nprotected amino acid is formed. Ϫ The crystal structure of 1a and 1c, compound 1a is remarkably stable against protolysis. Intermediates of hydrolysis of 1a, namely tris(tert-butyl)tri-(monoclinic, space group P2 1 /n) widely corresponds to the suggested configuration Ia, but reveals an envelope confor-phosphonic acid (2) and bis(tert-butyl)diphosphonic acid (3), can also be isolated in good yield. The structures of 1؊3 were mation for the six-membered ring with a P 3 O 2 plane in the crystal. In the crystal structure of the octahydrate of the diso-determined mainly by NMR spectroscopy ( 1 H, 13 C, 31 P). Assuming an energetic preference for the chair conformations dium salt of 2 (monoclinic, space group P2 1 /c), it can be seen that the polar end groups of the anions [tBu 3 P 3 O 7 ] 2Ϫ together in solution, and considering the steric requirements of the bulky substituents R, configurations Ia (point group C s , two with the water molecules and the Na + cations form hydrogen-bonded double-layers, strictly separated from each other R in equatorial positions) for 1a and b, and IIa (point group C 3v , all R equatorial) for 1c are suggested. Ϫ Reaction of 1a by the non-polar tert-butyl groups of the anions.