amines 2 through the concatenation of two catalytic cycles,
both promoted by PdI2, corresponding to oxidative ami-
nocarbonylation of the triple bond followed by cyclocarbo-
nylation (Scheme 1). To our knowledge, this is the first
500), in DME as the solvent at 100 °C and under 20 atm of
a 4:1 mixture of CO/air.
As reported in Table 1, excellent yields of 5-(carbamoyl-
methylene)oxazolidin-2-ones 3 (84-98% by GLC, 80-95%
isolated, entries 1-8) were obtained under these conditions
using cyclic secondary amines, such as morpholine 2a or
piperidine 2b, as nucleophiles, starting from variously
substituted 2-ynylamines (eq 1).6
Scheme 1. Sequential Catalysis Leading to 2-Oxazolidinones 3
Interestingly, the substrate conversion rate and product
yields were only slightly lower when the substrate to catalyst
ratio was raised to 300, as exemplified by the results reported
in entry 9 (to be compared with entry 1).
The reaction was slower using less nucleophilic acyclic
secondary amines, such as diethylamine 2c.7 Thus, the
reaction of 1a with 2c, carried out with a 1a/PdI2 molar ratio
of 50 rather than 100, led, after 24 h, to the corresponding
oxazolidinone 3ac in 67% isolated yield at 75% substrate
conversion (entry 10). Substrate conversion and product
isolated yield reached 100% and 79%, respectively, after 48
h (entry 11 and eq 1). Similar results were obtained starting
from 1b (entry 12 and eq 1).
Formation of the oxazolidinone derivative 3 can be
example of a sequential catalysis leading to 2-oxazolidinone
derivatives starting from acyclic precursors.4,5
Our method consists of the reaction of R,R-disubstituted
2-ynylamines 1 with CO, O2, and dialkylamines 2 in the
presence of catalytic amounts of PdI2 in conjunction with
KI and H2O (PdI2/KI/1/2/H2O molar ratio ) 1:10:100:500:
rationalized as shown in Scheme 2 (anionic iodide ligands
(5) For recent reviews on sequential catalysis, see: (a) Wasilke, J.-C.;
Obrey, S. J.; Baker, R. T.; Bazan, G. C. Chem. ReV. 2005, 105, 1001-
1020. (b) Lee, J. M.; Na, J.; Han, H.; Chang, S. Chem. Soc. ReV. 2004, 33,
302-312. (c) Fogg, D. E.; dos Santos, E. N. Coord. Chem. ReV. 2004,
248, 2365-2379. See also: (d) Multimetallic Catalysis in Organic Synthesis;
Shibasaki, M., Yamamoto, Y., Eds.; Wiley-VCH: Weinheim, 2004; pp 46-
48. For another recently reported example of sequential catalysis involving
PdI2, see: (e) Gabriele, B.; Mancuso, R.; Salerno, G.; Costa, M. AdV. Synth.
Catal. 2006, 348, 1101-1109. (f) Gabriele, B.; Mancuso, R.; Salerno, G.;
Veltri, L. Chem. Commun. 2005, 271-273.
(6) In a typical experiment, a 250 mL stainless steel autoclave was
charged with PdI2 (15.0 mg, 4.2 × 10-2 mmol), KI (70.0 mg, 0.42 mmol),
and a solution of 1 (4.2 mmol) and the amine 2 (21.0 mmol) in DME (8.4
mL). Water (380 mL, 21.1 mmol) was then added, and the autoclave was
sealed. While the mixture was stirred, the autoclave was charged with CO
(16 atm) and air (up to 20 atm), and then heated at 100 °C with stirring for
the required time. After cooling, the autoclave was degassed and opened.
The solvent was evaporated, and the products were purified by column
chromatography on neutral alumina using suitable hexane-AcOEt mixtures
as eluent (see the Supporting Information for further details).
(4) We have recently reported the synthesis of 4,4-dialkyl-5-[(methoxy-
carbonyl)methylene]oxazolidin-2-ones by Pd-catalyzed sequential oxidative
carboxylation-methoxycarbonylation of R,R-dialkyl substituted 2-ynyl-
amines: (a) Bacchi, A.; Chiusoli, G. P.; Costa, M.; Gabriele, B.; Righi, C.;
Salerno, G. Chem. Commun. 1997, 1209-1210. (b) Chiusoli, G. P.; Costa,
M.; Gabriele, B.; Salerno, G. J. Mol. Catal. A: Chem. 1999, 143, 297-
310. In that reaction, carbon dioxide was incorporated into the cycle, while
carbon monoxide was incorporated into the (methoxycarbonyl)methylene
moiety, so the process was completely different from that described in the
present work, in which both the carbonyl groups present in the final product
derive from carbon monoxide. The direct formation of 5-methylene-2-
oxazolidinones by carboxylation of 2-ynylamines has also been reported;
see, for example: (c) Costa, M.; Chiusoli, G. P.; Taffurelli, D.; Dalmonego,
G. J. Chem. Soc., Perkin Trans. 1 1998, 1541-1546. (d) Maggi, R.;
Bertolotti, C.; Orlandini, E.; Oro, C.; Sartori, G.; Selva, M. Tetrahedron
Lett. 2007, 48, 2131-2134.
(7) Primary amines afforded the corresponding symmetrical ureas,
according to a reactivity that we have already reported: Gabriele, B.;
Salerno, G.; Mancuso, R.; Costa, M. J. Org. Chem. 2004, 69, 4741-4750.
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Org. Lett., Vol. 9, No. 17, 2007