A new facile synthesis of tertiary dithioesters

Article abstract of DOI:10.1021/jo026162q

Thermal decomposition of tertiary azo compounds in the presence of a triphenylmethyl dithioester results in the formation of the corresponding tertiary dithioesters. This procedure is especially useful for the synthesis of tertiary phosphoryldithioformate

Full text of DOI:10.1021/jo026162q

readily obtained by reacting the appropriate sodium
dithioester with the pertinent primary or secondary alkyl
bromide (reaction 1), the preparation of the tertiary
dithioformates is less straightforward.
A New F a cile Syn th esis of Ter tia r y
Dith ioester s
Angelo Alberti,† Massimo Benaglia,*,†
Michele Laus,‡ and Katia Sparnacci‡
Istituto per la Sintesi Organica e la Fotoreattivita`,
ISOF-CNR, Area della Ricerca, Via P. Gobetti 101,
I-40129 Bologna, Italy, and Dipartimento di Scienze e
Tecnologie Avanzate, Corso Borsalino 54, INSTM,
UdR Alessandria, I-15100 Alessandria, Italy
Actually, two different routes leading to these
derivatives have been reported recently: the first con-
sists of the reaction of a bis(thiocarbonyl)disulfide
[RC(S)SSC(S)R] with an azo compound R′NdNR′, where
R′ is a tertiary alkyl group (reaction 2),8,9 while the second
involves the acid-catalyzed reaction of dithiocarboxylic
acids with an appropriate olefin (reaction 3).3
benaglia@area.bo.cnr.it
Received J uly 9, 2002
Abstr a ct: Thermal decomposition of tertiary azo com-
pounds in the presence of a triphenylmethyl dithioester
results in the formation of the corresponding tertiary
dithioesters. This procedure is especially useful for the
synthesis of tertiary phosphoryldithioformates, but also
represents an easy synthetic methodology of general ap-
plicability.
Dithioesters [RC(S)SR′] have been known for a long
time and their preparation and reactivity have been
widely investigated.1 More recently these compounds
attracted the attention of polymer chemists for their
ability to control radical polymerization: indeed the
RAFT (Reversible Addition Fragmentation chain Trans-
fer) radical polymerization of such monomers as styrene
and methacrylates is based on the use of these com-
pounds as transfer agents.2-4 In this respect, the behavior
of dithioesters is reminiscent of that of xanthates and
dithiocarbamates that also undergo radical addition-
fragmentation5 and have been used in controlled radical
polymerization.6 In order for the dithioesters to play such
a role efficiently, the R′ residues present in their mol-
ecules must be amenable to undergoing easy radical
displacement by the growing polymer radical, and there-
fore it must be an intrinsically resonance-stabilized
radical (benzyl, allyl, ...), a tertiary radical (tert-butyl,
2-cyanopropyl, ...), or a combination of the two (cumyl,
...).7 While primary and secondary dithioformates are
In the past few years we have studied the reactivity of
organic free radicals toward dithioformates bearing a
dialkoxyphosphoryl group bound to the thiocarbonyl
carbon,10-14 and following the results on the reaction of
benzyl diethoxyphosphoryl- and diethoxythiophos-
phoryldithioformates, we successfully exploited these two
derivatives as RAFT agents in the radical polymerization
of styrene.4 The results prompted us to investigate the
“RAFT efficiency” of other members of these families
where benzyl is replaced by a tertiary group. The
syntheses of these compounds through the easy and
inexpensive one-pot process used for the benzyl deriva-
tives (Scheme 1)11 were not considered worth trying due
to the inefficiency of nucleophilic substitution of tertiary
halides.
On the other hand, the two synthetic routes outlined
in reactions 2 and 3 also could not be used. In the former
case this was due to the impossibility of synthesizing the
necessary starting compounds. Indeed, while the required
disulfides RC(S)SSC(S)R can be readily synthesized when
* Author to whom correspondence should be addressed. Fax:
+39.051.6398349.
† ISOF-CNR.
‡ Dipartimento di Scienze e Tecnologie Avanzate.
(1) Duus, F. In Comprehensive Organic Chemistry; Barton, D., Ollis,
W. D., J ones, D. N. Eds.; Pergamon Press: Oxford, UK, 1979.
(2) Chiefari, J .; Chong, Y. K.; Ercole, F.; Krstina, J .; J effery, J .; Le,
T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.;
Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559. Mayadunne,
R. T. A.; Rizzardo, E.; Chiefari, J .; Krstina, J .; Moad, G.; Postma, A.;
Thang, S. H. Macromolecules 2000, 33, 243 and references therein.
(3) Barner-Kowollik, C.; Quinn, J . F.; Nguyen, T. L. U.; Heuts, J .
P. A.; Davis, T. P. Macromolecules 2001, 34, 7849.
(8) Bouhadir, G.; Legrand, N.; Quiclet-Sire, B.; Zard, S. Z. Tetra-
hedron Lett. 1999, 277.
(9) Thang, S. H.; Chong, Y. K.; Mayadunne, R. T. A.; Moad, G.;
Rizzardo, E. Tetrahedron Lett. 1999, 2435.
(10) Levillain, J .; Masson, S.; Hudson, A.; Alberti, A. J . Am. Chem.
Soc. 1993, 115, 8444.
(4) Laus, M.; Sparnacci, K.; Alberti, A.; Benaglia, M.; Macciantelli,
D. Macromolecules 2001, 34, 7629 and references therein.
(5) Zard, S. Z. Angew. Chem., Int. Ed. Engl. 1997, 36, 672.
(6) Otsu, T.; Yoshida, M. Makromol. Chem., Rapid Commun. 1982,
3, 127.
(7) Rizzardo, E.; Chiefari, J .; Chong, Y. K.; Ercole, F.; Krstina, J .;
J effery, J .; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C.
L.; Moad, G.; Thang, S. H. Macromol. Symp. 1999, 143, 291. Maya-
dunne, R. T. A.; Goto, A.; Sato, K.; Tsujii, Y.; Fukuda, T.; Moad, G.;
Rizzardo, E.; Thang, S. H. Macromolecules 2001, 34, 402.
(11) Alberti, A.; Benaglia, M.; Della Bona, M. A.; Macciantelli, D.;
Heuze´, B.; Masson, S.; Hudson, A. J . Chem. Soc., Perkin Trans. 2 1996,
1057.
(12) Alberti, A.; Benaglia, M.; Bonora, M.; Borzatta, V.; Hudson, A.;
Macciantelli, D.; Masson, S. Polym. Degrad. Stab. 1998, 62, 559.
(13) Alberti, A.; Benaglia, M.; Hapiot, P.; Hudson, A.; Le Coustomer,
G.; Macciantelli, D.; Masson, S. J . Chem. Soc., Perkin Trans. 2 2000,
1908.
(14) Alberti, A.; Benaglia, M.; Macciantelli, D.; Hudson, A.; Masson,
S. Magn. Reson. Chem. 2002, 40, 387.
10.1021/jo026162q CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/10/2002
J . Org. Chem. 2002, 67, 7911-7914
7911

TABLE 1. P r od u cts a n d Yield s of th e Th er m a l Rea ction
betw een Dith ioester s RC(S)SR′′ a n d Azocom p ou n d s
R′NdNR′
SCHEME 1
SCHEME 2
a
b
Toluene, reflux, 3 h. Ethyl acetate, reflux, 15 h.
•
displacement of the triphenylmethyl moiety by other R′
radicals.
SCHEME 3
We are not able to tell whether in the homolytic
displacement the release of the triphenylmethyl fragment
•
is synchronous to the addition of the tertiary R′ radical
or if a two-step process is involved where radical adduct
X is initially formed, but we wish to emphasize that we
have never been able to detect by EPR any adduct X
either in the present study concerning tertiary radicals
or in the previous study9 involving the addition of other
primary and secondary radicals to compound 1. The
driving force of this reaction stems from the stability of
triphenylmethyl radical, which makes its homolytic
displacement by the incoming •R′ very easy. On this basis,
the reaction is expected to occur also when replacing the
triphenylmethyl fragment with other readily displaceable
R′′ groups, although with a conversion related to the
stability of the individual leaving radical •R′′. The relative
stability of alkyl radicals formed by the S-R′′ bond
dissociation can be related to differences in the bond
dissociation energies BDE[R′′-H], the key argument being
that owing to the formation of H• as a common product
the energy required to break an individual bond reflects
the relative stability of the alkyl radical formed in each
case. Available BDE values for toluene (88 kcal mol-1),15
R is an alkyl, an aryl, an amino, an alkoxy, or a thioalkyl
residue, under no circumstances could we obtain the
analogous derivatives where R is a phosphorus-centered
group. The alternative route involving the reaction of
dithiocarboxylic acids with an appropriate olefin3 was
also unfeasible, because it likewise proved impossible to
prepare the starting dialkoxyphosphoryldithioformic acid.
triphenylmethane (81.1 kcal mol-1),16 and fluorene (79.8
kcal mol-1
)
indicate that the benzyl radical is signifi-
16
In the course of our studies on the addition of free
radicals to phosphoryl- and thiophosphoryldithiofor-
mates,11 we found that the reaction of Y• radicals with
triphenylmethyl diethoxyphosphoryldithioformate 1 led
to the EPR detection of the Ph3C• radical itself along with
the Y-adduct 3, implying the in situ formation of the
corresponding Y-dithioformate 2 (see Scheme 2). Prompted
by this finding we exploited this reaction as a synthetic
strategy leading to tertiary phosphoryldithioformates. We
report here that refluxing for 3 h a deaerated toluene
solution of compound 1 and an excess of AIBN leads to
the formation of 2-cyanoprop-2-yl diethoxyphosphoryl-
dithioformate 2a (yield 80% after chromatographic sepa-
ration). In a similar fashion, the use of other azo
compounds containing different tertiary alkyl residues
also leads to the formation of the corresponding diethoxy-
phosphoryldithioformates 2b-d , most likely through the
process outlined in Scheme 3 and involving homolytic
cantly less stable than the triphenylmethyl radical, which
in turn should be slightly less stable than the fluoren-
9-yl radical. We thus reacted AIBN with 9-fluorenyl
diethoxyphosphoryldithioformate 4 and with benzyl di-
ethoxyphosphoryldithioformate 5. In the former case the
reaction resulted again in the formation of the dithioester
2a , although in a lower conversion than in the case of 1
(see Table 1), while in the latter no displacement took
place and the starting compound 5 was recovered un-
reacted.
This last result may be associated with the lower
stability of the benzyl radical than the triphenylmethyl
radical, yet the conversion yield of the reaction involving
the fluoren-9-yl derivative 4 would be expected to be at
(15) Zhang, X.-M.; Bruno, J . W.; Enyinnaya, E. J . Org. Chem. 1998,
63, 4671.
(16) Zhang, X.-M.; Bordwell, G. G. J . Org. Chem. 1992, 57, 4163.
7912 J . Org. Chem., Vol. 67, No. 22, 2002

polymers at 60 °C after further addition of AIBN and the
corresponding monomer led to their complete conversion
with a molar mass distribution centered at higher molar
mass values, thus substantiating their “living” nature.
In conclusion, we believe that the reaction described
in Scheme 3 may represent a new useful tool in the hands
of synthetic chemists for the preparation of tertiary
dithioformates in general, and especially of tertiary
R-phosphorus-substituted derivatives.
Exp er im en ta l Section
All solvents were distilled and dried. Styrene (99%) and
methyl methacrylate (99%) were also distilled under vacuum just
before use. NMR spectra were recorded on either a 400-MHz or
on a 200-MHz spectrometer while mass spectra were obtained
by means of a high-resolution spectrometer.
F IGURE 1. SEC curves of poly(methyl methacrylate) (a) and
poly(styrene) (b) samples obtained using compound 2a as
RAFT agent.
Syn th etic P r oced u r es. (a ) Tr ip h en ylm eth yl d ieth oxy-
p h osp h or yld ith iofor m a te (1). A solution of diethyl phosphite
(2.99 g, 21.7 mmol) in THF (5 mL) was added dropwise to a
suspension of NaH (0.528 g, 22 mmol) in anhydrous THF (20
mL). After being refluxed for 5 min the solution was cooled to
-78 °C and CS2 (8.39 g, 110 mmol) was added. The solution was
allowed to warm to room temperature and stirring was continued
for 2 h. After the solution was cooled in an ice bath, Ph3CBr
(7.11 g, 22 mmol) was added and stirring was continued for 3 h
at room temperature. After CH2Cl2 (100 mL) was added the
solution was filtered, the solvent removed under reduced pres-
sure, and the residue quickly chromatographed (SiO2/ethyl
ether). Compound 1 was obtained as blue-violet crystals, mp 82
°C (8.12 g, yield 81%). 1H NMR (400 MHz) (CDCl3) δppm 1.315
(td, J 1,2 ) 7.6 Hz, J HP ) 0.76 Hz, 6H), 4.098-4.251 (m, 4H), 7.253
(s, 15H). 13C NMR (100 MHz) (CDCl3) δppm 17.85 (d, J CP ) 6.1
Hz), 28.186 (s), 65.818 (d, J CP ) 6.9 Hz), 128.614 (s), 128.894
(s), 131.351 (s), 225.351 (d, J CP ) 168.35 Hz).31P NMR (85 MHz)
(CDCl3) δppm from H3PO4-H2O 30%, -5.759. MS, m/z M+ absent,
243, 165.
(b) F lu or en -9-yl Dieth oxyp h osp h or yld ith iofor m a te (4).
A solution of diethyl phosphite (2.99 g, 21.7 mmol) in THF (5
mL) was added dropwise to a suspension of NaH (0.528 g, 22
mmol) in anhydrous THF (20 mL). After being refluxed for 5
min the solution was cooled to -78 °C and CS2 (8.39 g, 110
mmol) was added. The solution was allowed to warm to room
temperature and stirring continued for 2 h. 9-Bromofluorene
(5.39 g, 22 mmol) was added and stirring was continued for
another 3 h. The solvent was removed under reduced pressure,
ethyl ether was added to the residue, the insoluble salts were
filtered off, and the solution was flash chromatographed (elu-
ent: ethyl ether). Red crystals, mp 35 °C (5.40 g, yield 65%); 1H
NMR (400 MHz) (CDCl3) δppm 1.412 (t, J 1,2 ) 7.2 Hz, 6H), 4.342
(m, 4H), 6.642 (s, 1H), 7.283 (dd, J 1,2 ) J 1,2 ) 7.4 Hz, 2H), 7.422
(dd, J 1,2 ) J 1,2 ) 7.4 Hz, 2H), 7.476 (d, J 1,2 ) 7.4 Hz, 2H), 7.743
(d, J 1,2 ) 7.4 Hz, 2H); 13C NMR (100 MHz) (CDCl3) δppm 16.501
(d, J C,P ) 5.9 Hz), 51.178 (d, J C,P ) 3.2 Hz), 64.995 (d, J C,P ) 7.3
Hz), 120.103 (s), 125.015 (s), 127.581 (s), 128.784 (s), 141.067
(s), 141.317 (s), 228.392 (d, J C,P ) 173.2 Hz); 31P NMR (85 MHz)
(CDCl3) δppm from H3PO4/H2O 30%, -4.256; MS, m/z 378 (M+),
197, 182, 165; High-resolution MS calcd for [C18H19O3PS2]+
378.0513, found 378.0511.
least the same as that of the reaction of 1. While the
lower conversion observed with 4 seems to be in conflict
with the BDE[R-H] values, it has been recently pointed
out17 that the utmost care should be exerted when
relating radical stabilities to BDE[R-X] values, and that
this particular method leads to erroneous results in those
cases when X is not a hydrogen atom, unless additional
parameters are considered, such as the electronegativity
difference between the atoms or groups involved in the
bond to be broken. This would appear to be the case in
our reaction, that in fact involves cleavage of a carbon-
sulfur bond, which might account for the lower than
expected conversion observed for the reaction of AIBN
with the fluoren-9-yl diethoxyphosphoryldithioformate.
We believe this reaction represents a unique synthetic
route to tertiary R-phosphorus-substituted dithioesters.
On the other hand, it also can be applied with success to
the synthesis of tertiary dithiobenzoates and possibly of
tertiary dithioesters in general, although in these cases
other convenient routes to the reaction products are
available.3,8,9,18 As an example of this general applicabil-
ity, we have synthesized compound 7 by refluxing tri-
phenylmethyl dithiobenzoate 6 and AIBN in ethyl acetate
(see Table 1).
We also believe that the synthetic process outlined in
Scheme 3, although reminiscent of that described ear-
lier,8,9 is particularly relevant in that it provides an easy
and possibly unique access to a variety of tertiary
R-phosphorus-substituted dithioformates, which are valu-
able RAFT transfer agents in controlled radical poly-
merization processes. As an example, we have used
2-cyanoprop-2-yl diethoxyphosphoryldithioformate (2a ) to
control the AIBN-initiated polymerizations of styrene and
methyl methacrylate. Figure 1 shows the SEC curves of
the poly(styrene) and poly(methyl methacrylate) samples
we obtained by heating at 60 °C for 8 h a mixture of
monomer/2a /AIBN in a molar ratio of 935/1/0.185 for the
former and 630/1/0.526 for the latter case.
(c) Ben zyl Dieth oxyp h osp h or yld ith iofor m a te (5). A solu-
tion of diethyl phosphite (1.25 mL, 9.7 mmol) in THF (5 mL)
was added dropwise to a suspension of NaH (0.23 g, 9.7 mmol)
in anhydrous THF (10 mL). After being refluxed for 5 min the
solution was cooled to -78 °C and CS2 (2.9 mL, 48.1 mmol) was
added. The solution was allowed to warm to room temperature
and stirring continued for 2 h. Benzyl bromide (1.3 mL, 10.7
mmol) was added. After an additional hour hexane (30 mL) was
added, the solution filtered, the solvent evaporated, and the
residue quickly chromatographed (SiO2) using cyclohexane as
the first eluent to remove the impurities, then ethyl ether.
Compound 5 was obtained as a dark-red oil (2.3 g, 78% yield).
1H NMR (400 MHz) (CDCl3) δppm 1.36 (t, J 1,2 ) 7.6 Hz, 6H), 4.26
The resulting poly(styrene) sample, obtained in 3.4%
yield, had a number average molar mass Mn ) 9100 with
a polydispersity index Mw/Mn ) 1.33, whereas the poly-
(methyl methacrylate) sample, obtained in 44.0% yield,
showed Mn ) 38 200 with Mw/Mn ) 1.37. Heating of the
(17) Zavitsas, A. A. J . Chem. Edu. 2001, 78, 417.
(18) Le, T. P.; Moad, G.; Rizzardo, E.; Thang, S. H. PCT Interna-
tional Application WO 9801478 A1 980115, J an 25, 1998.
J . Org. Chem, Vol. 67, No. 22, 2002 7913

(m, 4H), 4.46 (s, 2H), 7.30 (s, 5H); 13C NMR (100 MHz) (CDCl3)
δppm 16.20 (d, J CP ) 6.34), 40.63 (d, J CP ) 2.72), 64.70 (d, J CP
6.94), 128.00 (s), 128.77 (s), 129.26 (s), 133.53 (s), 228.16 (d, J CP
) 174.54); 31P NMR (85 MHz) (CDCl3) δppm from H3PO4/H2O
30%, -4.57; MS m/z 304 (M+), 276, 248, 182, 121, 91.
J C,P ) 172.3 Hz); 31P NMR (85 MHz) (CDCl3) δppm from H3PO4/
H2O 30%, -7.233; MS, m/z 339 (M+), 280, 125, 109; high-
resolution MS calcd for [C11H18NO5PS2]+ 339.036405, found
339.036785.
)
(h ) 1-Cya n o-1-cycloh exyl Diet h oxyp h osp h or yld it h io-
for m a te (2d ). A carefully deaerated toluene solution (10 mL)
of 1 (0.2 g, 0.44 mmol) and azobis(2-cyanobutane) (0.12 g, 0.51
mmol) was refluxed for 3 h. The solvent was evaporated under
reduced pressure and the residue quickly chromatographed
(SiO2) using ethyl ether/toluene (30/70) as eluent. Compound 2d
was obtained as a purple-red oil (0.115 g, yield 82%). 1H NMR
(400 MHz) (CDCl3) δppm 1.362 (t, J 1,2 ) 7.2 Hz, 6H), 1.7-1.9 (m,
8H), 2.48-2.54 (m, 2H), 4.237 (m, 4H); 13C NMR (100 MHz)
(CDCl3) δppm 16.387 (d, J C,P ) 5.9 Hz), 22.719 (s), 25.906 (s),
34.372 (s), 48.373 (d, J C,P ) 5.5 Hz), 65.096 (d, J C,P ) 6.8 Hz),
117.065 (d, J C,P ) 1.3 Hz), 224.823 (d, J C,P ) 169.5 Hz); 31P NMR
(85 MHz) (CDCl3) δppm from H3PO4/H2O 30%, -6.831; MS, m/z
321 (M+), 245, 113, 138, 111; high-resolution MS calcd for
[C12H20NO3PS2]+ 321.062226, found 321.062369.
(i) 2-Cya n op r op -2-yl Dith ioben zoa te (7). A carefully de-
aerated ethyl acetate solution (10 mL) of 6 (0.2 g, 0.51 mmol)
and azobis(2-cyanobutane) (0.095 g, 0.58 mmol) was refluxed for
15 h. The solvent was evaporated under reduced pressure and
the residue quickly chromatographed (SiO2) using ethyl ether
as eluent. Compound 6 was obtained as a purple oil (0.078 g,
yield 70%). 1H NMR (400 MHz) (CDCl3) δppm 1.923 (s, 6H), 7.31-
7.64 (m, 3H), 7.87-7.98 (m, 2H); 13C NMR (100 MHz) (CDCl3)
δppm 26.234, 41.540, 119.785, 126.435, 128.365, 132.782, 144.267,
223.005; MS, m/z 221 (M+), 153, 121,77.
P olym er iza tion Stu d ies. Polymerizations of styrene and
methyl methacrylate in the presence of 2a as transfer agent were
carried out as described below. Average molar masses were
determined by SEC of THF solutions by means of a chromato-
graph equipped with refractive index and ultraviolet detectors,
using a PLgel MIXED-D column calibrated with polystyrene
standard samples.
(a ) RAF T Styr en e P olym er iza tion . A solution of styrene
(5.0 mL, 43.3 mmol), AIBN (1.4 mg, 8.6 µmol), and 2a (13.1 mg,
46.6 µmol) was placed in a polymerization ampule and degassed
by freeze and thaw cycles. The ampule was then sealed under
nitrogen. The polymerization was performed at 60 °C for 8 h.
The reaction mixture was diluted with CH2Cl2 and precipitated
into methanol, and the resulting polymer was washed with
methanol, purified by precipitation from CH2Cl2 into methanol,
then dried on silica gel in vacuo for several hours. Conversion
of styrene was 3.4% (estimated by weighting the obtained
polymer).
(d ) Tr ip h en ylm eth yl Dith ioben zoa te (6). A THF solution
(20 mL) of bromobenzene (1.34 mL, 12.7 mmol) was added
dropwise to a mixture of Mg (0.31 g, 12.8 mg atom) and a crystal
of I2 in THF (100 mL). After 3 h the reaction was cooled at 0 °C
and CS2 (0.988 g, 13 mmol) was added. When the addition was
over, the solution was allowed to reach room temperature.
Stirring was continued for ca. 2 h, then a solution of BrCPh3
(4.10 g, 12.7 mmol) in THF (15 mL) was added dropwise. After
another 3 h of stirring, CH2Cl2 (150 mL) was added, the solution
filtered, the solvent removed under reduced pressure, and the
residue quickly chromatographed (eluent hexane/CH2Cl2 80/20).
Compound 6 was obtained as a purple solid, mp 44 °C (5.02 g,
yield 80%). 1H NMR (400 MHz) (CDCl3) δppm 7.372 (m, 12H),
7.536 (d, J 1,2 ) 8 Hz, 6H), 8.018 (d, J 1,2 ) 8 Hz, 2H);13C NMR
(100 MHz) (CDCl3) δppm 74.979, 126.697, 127.021, 127.476,
127.937, 130.143, 131.546, 141.632, 145.779, 224.231; MS, m/z
396 (M+, weak), 243, 165.
(e) 2-Cya n op r op -2-yl Dieth oxyp h osp h or yld ith iofor m a te
(2a ). A carefully deaerated toluene (50 mL) solution of 1 (4.56
g, 10 mmol) and AIBN (3.52 g, 21.5 mmol) was refluxed for 3 h.
The solvent was evaporated under reduced pressure and the
residue quickly chromatographed (SiO2) using as eluent CH2Cl2/
ethyl ether/toluene (45/45/10). Compound 2a was obtained as a
deep red oil (2.25 g, yield 80%). Replacing compound 1 with
compound 4 (3.78 g, 10 mmol) lowered the yield to 54%. 1H NMR
(400 MHz) (CDCl3) δppm 1.369 (t, J 1,2 ) 7 Hz, 6H), 1.861 (s, 6H),
4.246 (m, 4H); 13C NMR (100 MHz) (CDCl3) δppm 16.387 (d, J C,P
) 5.9 Hz), 26.055 (s), 41.674 (d, J C,P ) 5.5 Hz), 65.147 (d, J C,P
)
6.9 Hz), 118.361 (s), 225.55 (d, J C,P ) 170 Hz); 31P NMR (85 MHz)
(CDCl3) δppm from H3PO4/H2O 30%, -6.791; MS, m/z 281 (M+),
213, 109, 91; high-resolution MS calcd for [C9H16NO3PS2]+
281.030926, found 281.031074.
(f) 2-Cya n obu t-2-yl Dieth oxyp h osp h or yld ith iofor m a te
(2b). A carefully deaerated ethyl acetate solution (10 mL) of 1
(0.2 g, 0.44 mmol) and azobis(2-cyanobutane) (0.1 g, 0.50 mmol)
was refluxed for 15 h. The solvent was evaporated under reduced
pressure and the residue quickly chromatographed (SiO2) using
ethyl ether as eluent. Compound 2b was obtained as a deep red
1
oil (0.112 g, yield 87%). H NMR (400 MHz) (CDCl3) δppm 1.172
(t, J 1,2 ) 7.2 Hz, 3H), 1.360 (t, J 1,2 ) 6.8 Hz, 6H), 1.824 (s, 3H),
2.017 (m, 1H), 2.181 (m, 1H), 4.236 (m, 4H); 13C NMR (100 MHz)
(CDCl3) δppm 9.183 (s), 16.378 (d, J C,P ) 5.9 Hz), 23.024 (s), 31.989
(s), 47.227 (d, J C,P ) 5.9 Hz), 61.117 (d, J C,P ) 7.1 Hz), 61.135
(d, J C,P ) 7.1 Hz), 171.413 (s), 225.294 (d, J C,P ) 170 Hz); 31P
NMR (85 MHz) (CDCl3) δppm from H3PO4/H2O 30%, -6.786; MS,
m/z 295 (M+), 280, 138, 109, 91; high-resolution MS calcd for
[C10H18NO3PS2]+ 295.046576, found 295.046709.
(b) RAF T Meth yl Meth a cr yla te P olym er iza tion . A solu-
tion of methyl methacrylate (3.7 mL, 34.7 mmol), AIBN (5.0 mg,
30.4 µmol), and 2a (15.6 mg, 55.6 µmol) in benzene (1.3 mL)
was placed in a polymerization ampule and degassed by freeze
and thaw cycles. The ampule was then sealed under nitrogen.
The polymerization was performed at 60 °C for 8 h. The reaction
mixture was diluted with CH2Cl2 and precipitated into methanol,
and the resulting polymer was washed with methanol, purified
by precipitation from CH2Cl2 into methanol, and dried on silica
gel in vacuo for several hours. Conversion of methyl methacry-
late was 44.0% (estimated by weighting the obtained polymer).
(g) 4-Car boxy-2-cyan obu t-2-yl Dieth oxyph osph or yldith io-
for m a te (2c). A carefully deaerated ethyl acetate solution (30
mL) of 1 (0.5 g, 1.1 mmol) and 4,4′-azobis(4-cyanovaleric acid)
(0.35 g, 1.26 mmol) was refluxed for 15 h. The solvent was
evaporated under reduced pressure and the residue chromato-
graphed on a reverse-phase RP18 using water/ACN (60/40) as
eluent. Compound 2c was obtained as a deep red oil (0.317 g,
1
Su p p or tin g In for m a tion Ava ila ble: 1H, 13C, and 31P
NMR spectra of compounds 1, 2a -d , 4, and 6. This material
is available free of charge via the Internet at http://pubs.acs.org.
yield 85%). H NMR (400 MHz) (CDCl3) δppm 1.325 (t, J 1,2 ) 7.2
Hz, 6H), 1.827 (s, 3H), 2.25-2.78 (m, 4H), 4.237 (m, 4H), 7.43
(br s, 1H); 13C NMR (100 MHz) (CDCl3) δppm 1.370 (d, J C,P ) 5.9
Hz), 23.636 (s), 29.406 (s), 32.988 (s), 45.642 (d, J C,P ) 5.9 Hz),
65.485 (d, J C,P ) 6.9 Hz), 116.867 (s), 174.829 (s), 224.814 (d,
J O026162Q
7914 J . Org. Chem., Vol. 67, No. 22, 2002