Alkali Metal Alkoxide Clusters
J . Org. Chem., Vol. 64, No. 5, 1999 1589
was removed in vacuo, and the phosphonate mixture was
filtered from the salts. The product was purified by column
chromatography (5% isopropyl alcohol in hexanes), giving 8.0
g of colorless oil in 89% yield. 1H NMR (300 MHz, CDCl3) δ
4.68-4.52 (m, 2H), 1.36 (d, J P-H ) 17.4 Hz, 3H), 1.23 (d, J HH
) 6.3 Hz, 12H) ppm; 13C{1H} NMR (75.5 MHz, CDCl3) δ 69.8,
23.9 (d, J P-C ) 6.4 Hz), 12.7 (d, J P-C ) 145 Hz) ppm; 31P{1H}
NMR (121.5 MHz, CDCl3) δ 28.3 ppm; IR (neat) 1244.2 cm-1
(PdO).19
they are the primary reactants in the reversible addition/
elimination sequence.16,17
Ben zyl Met h yl Met h ylp h osp h on a t e (C6H 5CH 2O)(C-
H3O)P (O)CH3. A reaction solution was prepared by combining
DMMP (125 mmol, 13.5 mL), benzyl acetate (25 mmol, 3.62
mL), and 125 mL of THF into a 250 mL Schlenk flask. The
reaction was initiated by transferring via syringe a 10 mL THF
solution of NaOtBu (2.5 mmol) to the reaction vessel. After 45
s, the reaction was quenched with saturated brine (2 mL).
Under these conditions, 94% of the benzyl acetate is consumed
to yield a 94:6 ratio of mono-:dibenzyl methylphosphonate.
THF was removed in vacuo, and the mixture of phosphonates
was filtered away from the salts. The excess DMMP and
unreacted benzyl acetate were removed by vacuum distillation
at 0.2 mmHg and 35 °C. Benzyl methyl methylphosphonate
was purified by column chromatography (37% acetone in
hexanes), giving 3.92 g of pale yellow oil (78% yield relative
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All esters were purchased from
Aldrich and were purified by distillation from CaH2 under inert
atmosphere prior to use. All alkali metal tert-butoxides were
purchased from Aldrich, purified by freshly subliming them,
and stored in a glovebox. THF was distilled from purple
sodium-benzophenone ketyl solution. All other solvents were
prepared by first purging reagent grade solvents with argon
and dried by passing over a column of activated alumina.18
Reaction vessels were prepared by flame-drying under a
nitrogen purge, and all preparative reactions were conducted
under a nitrogen atmosphere. Gas chromatography was per-
formed on HP-5 columns (30 m × 0.32 mm) with 1H, 13C, and
31P NMR spectra obtained at spectrometer frequencies of 300
or 400 MHz. All of the reported phosphonates are known
except for tert-butyl methyl methylphosphonate; their char-
acterization data are included for completeness.
1
to benzyl acetate). H NMR (300 MHz, CDCl3): δ 7.30 (br s,
5H), 4.98 (m, 2H), 3.57 (d, J P-H ) 11.1 Hz, 3H), 1.38 (d, J P-H
) 18.0 Hz, 3H) ppm; 13C{1H} NMR (75.5 MHz, CDCl3) δ 136.4
(d, J PC ) 7.6 Hz), 128.6, 128.4, 128.1, 67.1 (d, J PC ) 6.0 Hz),
52.1 (d, J PC ) 4.0 Hz), 10.8 (d, J P-C ) 143.7 Hz) ppm; 31P{1H}
NMR (121.5 MHz, CDCl3) δ 32.47 ppm; IR (neat) 1244.3 cm-1
(PdO).8a
Isop r op yl Meth yl Meth ylp h osp h on a te (iP r O)(CH3O)P -
(O)CH3. A biphasic reaction solution was prepared by com-
bining DMMP (100 mmol, 10.8 mL), isopropyl acetate (400
mmol, 46.8 mL), and 250 mL of hexanes in a 500 mL Schlenk
flask under nitrogen. A KOtBu solution (280 mg, 2.5 mmol, 5
mol % in 50 mL THF) was transferred via syringe into the
ester-containing flask, resulting in a cloudy single-phase
reaction mixture which was stirred for ∼30 s and then
quenched with 1 mL of brine. Under these conditions, IMMP
was produced as the major product (DMMP:IMMP:DIMP )
7:86:7). The reaction mixture was decanted away from the
salts, solvent and acetates were removed in vacuo, and the
product was purified by column chromatography (10% ethanol
in hexanes), giving 11.8 g of colorless oil in 78% yield. 1H NMR
(300 MHz, CDCl3) δ 4.57 (d septet, J P-H ) 7.8, J H-H ) 6.3 Hz,
1H), 3.47 (d, J P-H ) 11.1, 3H), 1.23 (d, J P-H ) 17.7, 3H), 1.07
(d, J H-H ) 6.3, 6H) ppm; 13C{1H} NMR (75.5 MHz, CDCl3) δ
70.1 (d, J P-C ) 6.4 Hz), 51.7 (d, J P-C ) 6.4 Hz), 23.8, 10.9 (d,
J P-C ) 145.6) ppm; 31P{1H} (121.5 MHz, CDCl3) δ 30.9 ppm;
IR (neat) 1243.5 cm-1 (PdO).6,8b
Diben zyl Meth ylp h osp h on a te (C6H5CH2O)2P (O)CH3.
DMMP (50 mmol, 1.08 mL) and benzyl acetate (250 mmol, 36
mL) were syringed into a 250 mL Schlenk flask that had
previously been flame-dried under a nitrogen purge. In a
separate 250 mL Schlenk flask was prepared a catalyst
solution from KOtBu (4 mmol, 450 mg), hexanes (175 mL), and
THF (25 mL). Aliquots of this catalyst solution (20 mL, 1 mol
%) were syringed into the phosphonate-bearing flask, stirred
for 5 min, and evacuated for 5 min to remove methyl acetate.
Addition of catalyst aliquots (20 mL), followed by evacuation
of the volatiles, was repeated seven additional times until the
desired 98% conversion to product was achieved (confirmed
by 31P NMR). The salts were filtered from the ester mixture,
and the excess benzyl acetate was separated from the product
by distillation at 0.2 mmHg and 35 °C. The product was then
purified through a plug of silica gel eluted with 100% ethyl
acetate to give 12.9 g of colorless oil in 94% yield. 1H NMR
(300 MHz, CDCl3) δ 7.32 (s, 10 H), 4.99 (m, 4 H), 1.46 ppm (d,
J H-P ) 17.7 Hz, 3H); 13C{1H} NMR (75.5 MHz, CDCl3) δ 136.35
(d, J PC ) 7.6 Hz), 128.6, 128.4, 127.9, 67.08 (d, J PC ) 6.0 Hz),
11.7 (d, J P-C ) 145.0 Hz) ppm; 31P{1H} NMR (121.5 MHz,
CDCl3) δ 31.8 ppm; IR (neat) 1242.6 cm-1 (PdO).4
ter t-Bu t yl Met h yl Met h ylp h osp h on a t e ((CH3)3CO)-
(CH3O)P (O)CH3. A hexanes solution (100 mL) of DMMP (25
mmol, 2.7 mL) was prepared in a 150 mL three-necked flask
under nitrogen. Two pressure-equalizing addition funnels were
fitted to the reaction vessel to which were added tert-butyl
acetate (50 mmol, 6.74 mL) and a 10 mL THF solution of KOt-
Bu (140 mg, 5 mol %). The acetate and catalyst solutions were
each separately dripped into the reaction over ∼5 min. After
stirring for an additional 10 min, the reaction solution was a
deep golden yellow with small crystals forming on the flask
surface. 31P NMR analysis indicated a 49% conversion to
product. The solution was decanted, solvent and acetates were
removed in vacuo, and the product was purified by column
chromatography (30% acetone in hexanes), to give 2.0 g of pale
yellow oil in 48% overall yield (>97% purity). High concentra-
tions of tert-butyl acetate appear to inhibit catalysis; the slow
Diisop r op yl Meth ylp h osp h on a te (iP r O)2P (O)Me. Two
separate solutions of isopropyl acetate (400 mmol, 47 mL) in
hexanes (115 mL), and KOtBu (450 mg, 4 mmol, 8 mol %) in
THF (40 mL), were prepared in 250 and 50 mL Schlenk flasks,
respectively. The reaction was initiated by transferring via
syringe solutions of acetate (20 mL, ∼1 equiv) and catalyst (5
mL, 1 mol %) into a 250 mL Schlenk flask containing DMMP
(50 mmol, 5.4 mL). The reaction was stirred magnetically for
5 min, and the volatile components were removed in vacuo.
The acetate/catalyst addition and evacuation steps were
repeated seven additional times to reach a conversion of 94%
diisopropyl methylphosphonate and 6% isopropyl methyl me-
thylphosphonate (confirmed by 31P NMR). All volatile material
1
addition protocol alleviates this. H NMR (300 MHz, CDCl3):
(16) (a) J ackman, L. M.; Chen, X. J . Am. Chem. Soc. 1997, 119,
8681-8684. (b) J ackman, L. M.; Petrei, M. M.; Smith, B. D. J . J . Am.
Chem. Soc. 1991, 113, 3451-3458.
δ 3.57 (d, J P-H ) 10.4, 3H), 1.38 (s, 9H), 1.31 (d, J P-H ) 16.7
Hz, 3H) ppm; 13C{1H} NMR (100.6 MHz, CDCl3) δ 82.19 (d,
J P-C ) 8.6 Hz), 51.72 (d, J P-C ) 6.1 Hz), 30.35 (d, J P-C ) 3.6
(17) Since NaOMe is an insoluble sheetlike material, the catalyst
is most reasonably in a solubilized form: (a) Weiss, von E.; Alsdorf,
H. Z. Anorg. Chem. 1970, 372, 206-213. (b) Weiss, von E. Z. Anorg.
Allg. Chem. 1964, 332, 197-203.
(19) (a) Chakraborty, S. K.; Engel, R. Synth. Commun. 1991, 21,
1039-1046. (b) Meyrick, C. I.; Thompson, H. W. J . Chem. Soc. 1950,
225-229.
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.