D. G. Gilheany et al.
[2] a) J. I. G. Cadogan, in Organophosphorus Reagents in Organic Syn-
thesis (Eds: J. I. G. Cadogan), Academic Press, New York, 1979;
b) Organophosphorus Reagents (Ed.: P. J. Murphy), Oxford Univer-
sity Press, Oxford, 2004; c) P. A. Byrne, D. G. Gilheany, Chem. Soc.
and phosphinous acid derivatives is now, in principle, much
easier.
Conclusion
[3] For the use of phosphines in metal-based catalysis, see: a) Compre-
hensive Asymmetric Catalysis, Vol. I-III (Eds.: E. N. Jacobsen, A.
Pfaltz, H. Yamamoto), Springer, Berlin, 1999; b) Catalytic Asymmet-
ric Synthesis (Ed.: I. Ojima), 3rd ed., Wiley, New York, 2010; c) S.
Chiral Ligands and Catalysts (Ed.: Q.-L. Zhou), Wiley-VCH, Wein-
heim, 2011.
[4] For the use of phosphines as organocatalysts, see: a) J. G. Verkade,
2008, 37, 1140; d) C. J. O’Brien, J. L. Tellez, Z. S. Nixon, L. J. Kang,
A. L. Carter, S. R. Kunkel, K. C. Przeworski, G. A. Chass, Angew.
Chem. 2009, 121, 6968; Angew. Chem. Int. Ed. 2009, 48, 6836; e) M.
Zablocka, A. Hameau, A. M. Caminade, J. P. Majoral, Adv. Synth.
[5] a) L. Maier, in Organic Phosphorus Compounds, Vol. 1 (Eds.: L.
Maier, G. M. Kosolapoff), Wiley-Interscience, New York, 1972,
Ch. 1, pp. 1–226; b) P. Beck, in Organic Phosphorus Compounds
Vol. 2 (Eds.: L. Maier, G. M. Kosolapoff), Wiley-Interscience, New
York, 1972, Ch. 4, pp. 189–508; c) D. G. Gilheany, C. M. Mitchell in
The Chemistry of Organophosphorus Compounds, Vol. 1 (Ed.: F. R.
Hartley), Wiley-Interscience, Chichester, 1990, Ch. 7, pp. 151–190;
d) M. J. Gallagher, in The Chemistry of Organophosphorus Com-
pounds, Vol. 2 (Ed.: F. R. Hartley), Wiley-Interscience, Chichester,
1992, Ch. 2, pp. 53–76.
In summary, we present an unprecedented high-yielding
aminophosphine oxide deoxygenation, with no phosphorus–
nitrogen bond cleavage. Furthermore the product is the pro-
tected borane adduct, allowing easy manipulation. The
methodology breaks the transformation down into two
steps, first breaking the very strong phosphoryl bond, replac-
ing the oxygen with the better leaving group, chloride. This
facilitates subsequent reduction with safe and cheap sodium
borohydride, allowing the presence of, for example, ester
functional groups. We believe that this new methodology
opens up completely new synthetic strategies in organophos-
phorus chemistry because nitrogen (and oxygen by proxy)
substituents can now be attached to PV centers and be re-
tained on conversion to PIII.
Experimental Section
General procedure for deoxygenation of aminophosphine oxides and sul-
fides: To
a stirred solution of aminophosphine oxide or sulfide
(1.0 mmol) in toluene (2 mL) was added oxalyl chloride (1.0 mmol) dis-
solved in toluene (2 mL) dropwise at room temperature under a nitrogen
atmosphere. The formation of chlorophosphonium salt (CPS) at this
point was normally evident by vigorous gas evolution and was confirmed
by 31P NMR spectroscopy of the reaction mixture. In some cases noted in
the Supporting Information, where the gas evolution was less pro-
nounced, the mixture had to be heated to 708C (approximate boiling
point of oxalyl chloride) for one hour to effect complete conversion to
CPS. Alternatively in those cases, the reaction could be left at room tem-
perature overnight. After formation of CPS (typically 30 min), sodium
borohydride (2.1 mmol) dissolved in diglyme (ca. 3 mL) was added drop-
wise to the reaction mixture and heated to 708C for one hour, after
which 31P NMR spectroscopy shows full completion of CPS to phosphine
borane (as indicated by characteristic quartet splitting). The reaction
mixture was washed with deionized water (2ꢁ5 mL) and the isolated or-
ganic layer was dried over anhydrous MgSO4. The drying agent was re-
moved by filtration, and the toluene was removed in vacuo to give a col-
orless solution, which was eluted through a silica plug first with cyclohex-
ane to remove the high boiling diglyme then with 50:50 cyclohexane/
ethyl acetate to isolate the aminophosphine borane product. Solvent re-
moval in vacuo yielded the pure aminophosphine borane.
[6] Electrochemical reduction: T. Yano, M. Hoshino, M. Kuroboshi, H.
Tanaka, Synlett 2010, 5, 801.
[7] Metal hydride reductants: a) T. Imamoto, T. Oshiki, T. Onozawa, T.
vich, M. Fekete, T. Chuluunbaatar, A. Dobꢄ, V. Harmatc, L. Toke,
K. M. Pietrusiewicz, Synlett 2003, 1012; g) C. A. Busacca, R. Raju,
N. Grinberg, N. Haddad, P. James-Jones, H. Lee, J. C. Lorenz, A.
Byrne, K. V. Rajendran, J. Muldoon, D. G. Gilheany, Org. Biomol.
[8] Silane reductants: a) K. Naumann, G. Zon, K. Mislow, J. Am. Chem.
e) C. Petit, A. Favre-Reguillon, B. Albela, L. Bonneviot, G. Migna-
Li, L.-Q. Lu, S. Das, S. Pisiewicz, K. Junge, M. Beller, J. Am. Chem.
Acknowledgements
[9] a) P. D. Henson, S. B. Ockrymiek, J. Raymond, E. Markham, J. Org.
b) L. D. Quin, J. Szewczyk, Phosphorus Sulfur Relat. Elem. 1984, 21,
161.
We thank sincerely Science Foundation Ireland (SFI) for funding this
chemistry under Grant 09/IN.1/B2627. We are also grateful to the UCD
Centre for Synthesis and Chemical Biology (CSCB) and the UCD School
of Chemistry and Chemical Biology for access to their extensive analysis
facilities, as well as to Dr. Helge Mꢂller Bunz for X-ray analysis. We also
thank the EU COST Network PhosSciNet. D.G.G. also thanks the Uni-
versity College Dublin for a Presidentꢃs Research Fellowship, held partly
in Stanford University in the Laboratory of Professor James Collman.
[11] Encompassing phosphinamides, phosphonamides, and phosphor-
AHCTUNGTRENGNaUN mides.
ic case, the phosphinamide is part of a six-membered ring system,
which may explain its stability.
[13] a) L. D. Quin, G. Keglevich, J. Chem. Soc. Perkin Trans. 2 1986, 7,
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