B. Gabriele et al. / Tetrahedron Letters 50 (2009) 7330–7332
7331
Table 1
HI. Complex I may then undergo intramolecular nucleophilic dis-
placement by the second hydroxyl group, with formation of 2a
and elimination of Pd(0) and HI. Alternatively, intermediate I
may convert into palladacycle derivative II with elimination of
HI. Reductive elimination eventually leads to the final product
and Pd(0). In any case, Pd(0) is then reoxidized to PdI2 according
to the mechanism we demonstrated several years ago,18 involving
initial oxidation of HI by O2 to give I2 followed by oxidative addi-
tion of the latter to Pd(0).
In conclusion, we have developed the first general method for
the catalytic direct oxidative carbonylation of both 1,2- and 1,3-
diols, to give the corresponding cyclic carbonates in good to excel-
lent yields (66–94%) and high catalytic efficiencies (up to ca.
190 mol of product per mol of palladium). The present phosgene-
free, atom-economical approach for the preparation of cyclic car-
bonates thus represents a valuable alternative to the currently
known methods for their production.
Synthesis of 5-membered and 6-membered cyclic carbonates 2a–f by PdI2/KI-
catalyzed oxidative carbonylation 1,2- and 1,3-diols 1a–fa
R2
R2
R1
R1
n
Pd cat
H2O
O H n
+ CO + (1/2) O2
O
O
OH
1a-f
O
2a-f
Entry
n
R1
R2
1
1: PdI2
molar
ratio
Time Conversion
2
Yield
of
(h)
of 1 (%)b
2 (%)c
1
2
3
4
5
6
7
0
0
0
1
1
1
1
H
H
H
H
H
H
H
1a 200
1b 200
1c 200
1d 200
1d 100
1e 100
15
15
15
15
15
24
24
100
100
100
80
100
100
100
2a 84
Et
Ph
H
H
Me
H
2b 94
2c 94
2d 42
2d 74
2e 66
Me 1f
100
2f
68
a
All reactions were carried out in DMA (substrate concentration = 0.5 mmol of 1/
mL of DMA, 4 mmol scale based on 1) at 100 °C under 20 atm of a 4:1 mixture of
Acknowledgments
CO-air in the presence of PdI2 in conjunction with 10 equiv of KI.
b
Determined by GLC.
Isolated yield based on starting 1.
c
This work was supported by the Ministero dell’Università e del-
la Ricerca (MIUR, Rome, Italy) (Progetto di Ricerca d’Interesse Naz-
ionale PRIN 2006031888).
cyclic carbonates 2b–c with isolated yields higher than 90% (Ta-
ble 1, entries 2 and 3).11,13
References and notes
Our method could also be successfully applied to the first direct
catalytic oxidative carbonylation of 1,3-diols, such as 1,3-propane-
diol 1d (n = 1, R1 = R2 = H), 1,3-butanediol 1e (n = 1, R1 = Me,
R2 = H), and 2-methylpropane-1,3-diol 1f (n = 1, R1 = H, R2 = Me)
to give the corresponding [1,3]dioxan-2-ones 2d–f in good yields
(Table 1, entries 4–7). As expected in view of their higher confor-
mational mobility, 1,3-diols turned out to be less reactive with re-
spect to 1,2-diols: thus, the reaction of 1d, carried out under the
same conditions as previously employed for 1,2-diols 1a–c (Table 1,
entries 1–3), led to a substrate conversion of 80%, with an isolated
yield of [1,3]dioxan-2-one 2d of 42% (Table 1, entry 4). Better re-
sults were however obtained by working with a lower substrate-
to-catalyst molar ratio: with 1 mol % of PdI2, the substrate conver-
sion was quantitative after 15 h, and the yield of 2d increased to
74% (Table 1, entry 5). Under the same conditions, the reactions
of 1e and 1f were slightly slower: the substrate conversion reached
100% after 24 h, with isolated yields of the corresponding 6-mem-
bered cyclic carbonates 2e and 2f of 66% and 68%, respectively (Ta-
ble 1, entries 6 and 7).14–16
1. For reviews, see: (a) Clemens, J. H. Ind. Eng. Chem. Res. 2003, 42, 663–674; (b)
Parrish, J. P.; Salvatore, R. N.; Jung, K. W. Tetrahedron 2000, 56, 8207–8237.
2. For reviews, see: (a) Shaikh, A.-A. G.; Sivaram, S. Chem. Rev. 1996, 96, 951–976;
(b) Kas’yan, L. I.; Tarabara, I. N.; Kas’yan, A. O. Russ. J. Org. Chem. 2004, 40, 1227–
1257; (c) Sun, J.; Fujita, S.; Arai, M. J. Organomet. Chem. 2005, 690, 3490–3497;
(d) Darensbourg, D. J. Chem. Rev. 2007, 107, 2388–2410; (e) Sakakura, T.;
Kohno, K. Chem. Commun. 2009, 1312–1330.
3. For a recent review on the importance of the development of new atom-
economical processes, see: Trost, B. M. Acc. Chem. Res. 2002, 35, 695–705.
4. Tam, W. J. Org. Chem. 1986, 51, 2977–2981.
5. Recently, the stoichiometric formation of [1,3]dioxolan-2-one by basic
treatment of complex PdCl(PN)(CO2CH2CH2OH) [in its turn obtained by
carbonylation of PdCl2(PN), PN = 2-(b-diphenylphosphine)ethylpyridine] was
also described: Giannoccaro, P.; Cornacchia, D.; Doronzo, S.; Mesto, E.;
Quaranta, E.; Aresta, M. Organometallics 2006, 25, 2872–2879.
6. (a) Analysis of the patent literature revealed another example of formation of a
cyclic carbonate by sub-stoichiometric oxidative carbonylation of a diol: it
refers to the reaction of ethylene glycol, which was used as the reaction
solvent, in the presence of Co(OAc)2 as the catalyst and O2 as the oxidant (CO/
O2 = 20 atm:10 atm at 100 °C): Delledonne, D.; Rivetti, F.; Romano, U. Eur. Pat.
Appl. EP 463678A2, 1992.; The yield of the cyclic carbonate, based on starting
ethylene glycol, was only 2%, and the catalytic turnover was 1.7. It should also
be pointed out that a 2:1 mixture of CO–O2 at 100 °C is potentially explosive, as
the flammability range for CO in O2 is 16.7–93.5% at room temperature, and it
becomes even larger at higher temperatures, see: (b) Bartish, C. M.; Drissel, G.
M., 3rd ed.. In Kirk-Othmer Encyclopedia of Chemical Technology; Grayson, M.,
Eckroth, D., Bushey, G. J., Campbell, L., Klingsberg, A., van Nes, L., Eds.; Wiley-
Interscience: New York, 1978; Vol. 4, p 774.
7. (a) Gabriele, B.; Salerno, G.; Brindisi, D.; Costa, M.; Chiusoli, G. P. Org. Lett. 2000,
2, 625–627; (b) Gabriele, B.; Mancuso, R.; Salerno, G.; Costa, M. J. Org. Chem.
2003, 68, 601–604.
8. (a) Gabriele, B.; Mancuso, R.; Salerno, G.; Costa, M. Chem. Commun. 2003, 486–
487; (b) Gabriele, B.; Salerno, G.; Mancuso, R.; Costa, M. J. Org. Chem. 2004, 69,
4741–4750.
9. These conditions (16 atm of CO together with 5 total atm of air, considering
that the autoclave was loaded under 1 atm of air) corresponded to 76.2% of CO
in air and were outside the explosion limits for CO in air (ca. 16–70% at 18–
20 °C and atmospheric pressure, 14.8–71.4% at 100 °C and atmospheric
pressure. At higher total pressure, the range of flammability decreases: for
example, at 20 atm and 20 °C the limits are ca. 19 and 60%. See: Bartish, C. M.;
Drissel, G. M., 3rd ed.. In Kirk-Othmer Encyclopedia of Chemical Technology;
Grayson, M., Eckroth, D., Bushey, G. J., Campbell, L., Klingsberg, A., van Nes, L.,
Eds.; Wiley-Interscience: New York, 1978; Vol. 4, p 775.
10. Under Tam’s conditions, no catalytic conversion of 1a into 2a was observed:
the author reported that ‘Attempts to make the reaction with ethylene glycol
catalytic in palladium fail probably due to the interaction of ethylene glycol
with CuC12; no carbonate is formed’ (Ref. 4). As regards the oxidative
carbonylation of 1a carried out in the presence of Co(OAc)2, see note 6.
11. Typical carbonylation procedure for the synthesis of 5-membered cyclic
On the basis of what is already known on PdI2-catalyzed oxida-
tive carbonylation reactions,17 formation of 2a may be interpreted
as occurring as shown in Scheme 1 (anionic iodide ligands are
omitted for clarity). Thus, formation of the alkoxycarbonylpalladi-
um species I takes place through the reaction between the alco-
holic function of the substrate, CO, and PdI2, with elimination of
R2
R2
O H n
R1
R1
n
O
+ CO + PdI2
OH
PdI
HI
OH
O
1
I
[Pd(0)+HI]
HI
R2
R1
O
n
O
Pd
2
Pd(0)
O
II
PdI2 + H2O
Pd(0) + 2 HI + (1/2) O2
carbonates 2a–c:
a 250 mL stainless steel autoclave was charged in the
presence of air with PdI2 (7.0 mg, 1.94 ꢀ 10ꢁ2 mmol), KI (32.0 mg,
1.93 ꢀ 10ꢁ1 mmol) and a solution of 1a–c (3.88 mmol) in DMA (7.8 mL). The
Scheme 1. Mechanism of the PdI2-catalyzed oxidative carbonylation of diols 1 to
give cyclic carbonates 2. Anionic iodide ligands are omitted for clarity.