m-Oxobis[tris(dimethylamino)phosphonium] Bis(tetrafluoroborate)1

[55881-03-3]  · C12H36B2F8N6OP2  · m-Oxobis[tris(dimethylamino)phosphonium] Bis(tetrafluoroborate)  · (MW 516.10)

(a mild dehydrating agent, useful in peptide synthesis,2 dehydration of aldoximes to nitriles3 and Beckmann or Lossen-type rearangements3)

Alternate Name: Bates' reagent.

Physical Data: mp 194-204 °C.

Solubility: insol ether, EtOAc, THF, CH2Cl2, CHCl3; sol MeCN, DMF, HMPA.

Form Supplied in: white crystalline solid; limited commercial availability.

Preparative Methods: by treatment of Hexamethylphosphoric Triamide with p-toluenesulfonic anhydride at 55 °C for 3 h, isolation of the bis(p-toluenesulfonate), then treatment with NaBF4 in MeCN.2

Handling, Storage, and Precautions: can be used with care without special precautions; however, it reacts with water to produce HMPA (carcinogenic) and HBF4 (corrosive).

Peptide Synthesis.

Bates' reagent is a dehydrating agent used in the synthesis of peptides (eq 1).1 It has the advantage over 1,3-Dicyclohexylcarbodiimide (DCC) that the byproducts of the reaction (HMPA, etc.) are water-soluble and easily removed. A disadvantage is that it results in extensive racemization. This can be overcome, however, by the addition of 1-Hydroxybenzotriazole (HOBT).1 Bates' reagent, even in conjunction with HOBT, is not as popular as the closely related reagent Benzotriazol-1-yloxytris(dimethylamino)phosphonium Hexafluorophosphate (BOP).4 The latter reagent is more readily available, considerably cheaper, has a lower molecular weight (less reagent is required), produces less acid (less base is required), and is more efficient for solid-phase peptide synthesis.5

Activation of N-Hydroxy Compounds.

Bates' reagent is a useful reagent for the Beckmann rearrangement of ketoximes (eq 2), dehydration of aldoximes to nitriles (eq 3), and Lossen-type rearrangement of hydroxamic acids (eq 4).3

It is much less reactive as an activating/dehydrating agent than is the analogous Ph3+P-O-+PPh3 2OTf-,6 where reactions are often complete in a few minutes at rt. However, a disadvantage of the latter reagent is the difficulty of separating the product from Ph3PO.

1. FF 1977, 6, 425.
2. Bates, A. J.; Galpin, I. J.: Hallett, A.; Hudson, D.; Kenner, G. W.; Ramage, R. HCA 1975, 58, 688.
3. Galpin, I. J.; Gordon, P. F.; Ramage, R.; Thorpe, W. D. T 1976, 32, 2417.
4. Castro, B.; Dormoy, J. R.; Evin, G.; Selve, C. TL 1975, 1219.
5. Hudson, D. JOC 1988, 53, 617.
6. Hendrickson, J. B.; Hussoin, Md. S. JOC 1987, 52, 4137; 1989, 54, 1144.

Ian D. Jenkins

Griffith University, Brisbane, Australia

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