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K. Sekine et al.
Letter
Synlett
lectivity toward the Z-isomers (entry 2). Moreover, the sil-
ver catalyst is assumed to promote a different reaction
pathway, for example, by acting as a Lewis acid to an elec-
tron-withdrawing group.7 In other words, for substrates
1a–n and 1q, which were transformed into the correspond-
ing (Z)-oxazolidinones with a high selectivity, the silver cat-
alyst plays a crucial role as a π-Lewis acid in efficiently pro-
moting the cyclization through anti-addition and produc-
ing the corresponding oxazolidinones with a high Z-
selectivity.
In summary, the highly Z-selective oxazolidinone syn-
theses from propargylic alcohols containing internal
alkynes and phenyl isocyanate were achieved by the combi-
nation of AgOAc and DMAP. The catalytic system was ap-
plied to propargylic alcohols bearing alkyl-substituted
alkynes. Considering the results with or without an elec-
tron-withdrawing group on the aromatics, it was found that
the silver catalyst effectively activated the C–C triple bond
as a -Lewis acid to produce the corresponding oxazolidi-
nones with high Z-selectivities.
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Supporting Information
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(6) (4Z)-4-Benzylidene-5,5-dimethyl-3-phenyl-1,3-oxazolidin-
2-one; Typical Procedure
Supporting information for this article is available online at
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References and Notes
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A mixture of AgOAc (6.7 mg, 10 mol%) and DMAP (14.7 mg, 30
mol%) in 1,2-Cl2C6H4 (0.5 mL) was stirred for 15 min under N2, A
solution of the propargylic alcohol 1a (64.1 mg, 0.4 mmol) in
1,2-Cl2C6H4 (0.75 mL) was added, followed by a solution of
PhNCO (65 μL, 1.5 equiv) in 1,2-Cl2C6H4 (0.75 mL), and the
mixture was stirred at 40 °C for 9 h. The reaction was quenched
with H2O, and the mixture was extracted with EtOAc (3 ×). The
organic layers were combined, washed with brine, and dried
(Na2SO4). The E/Z ratio was measured by GC analysis of the
crude mixture. The solvent was then removed under reduced
pressure, and the residue was purified by column chromatogra-
phy (silica gel, hexane–EtOAc) to give oxazolidinone 3a as color-
less solid; yield: 105.4 mg (94%); 1H NMR (400 MHz, CDCl3):
δ = 1.73 (s, 6 H), 5.63 (s, 1 H), 6.66 (d, J = 7.3 Hz, 2 H), 6.82–6.92
(m, 3 H), 6.98–7.06 (m, 5 H).
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(7) It is also possible that isomerization of the vinylsilver interme-
diate produced the (E)-oxazolidinone, but the detail remains
unclear.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2447–2450