X. Qi et al. / Journal of Catalysis 381 (2020) 215–221
217
Table 1
entry 5). The reactions delivered unsatisfactory yields of 2a with
alternative bidentate phosphine ligands such as DPPE, DPPB, Xant-
phos, DPPF, and BINAP (Table 1, entry 7). Specifically with DPPP,
the yield was significantly decreased when the ligand-to-metal
ratio was changed to 1:1 or 2:1, which implies that there might
be two different rhodium-phosphine complexes for decarbonyla-
tion and carbonylation respectively (Table 1, entries 8–9). The base
was also critical for the reaction as the target product was not
detected when organic base such as Et3N, DBU and DiPEA were
used (Table 1, entry 10). Intriguingly, compared to Na2CO3, carbon-
ates bearing other alkali metal cations displayed no or little reac-
tivity (Table 1, entry 11). Other sodium bases screened delivered
the furfuryl ester in lower yield (Table 1, entry 12). Furthermore,
4 Å MS turned out to be vital to increase the reaction efficiency
(Table 1, entry 13). Finally, when the reaction time extended to
30 h, the yield of product decreased (Table 1, entry 14).
With the optimized reaction conditions in hand, the substrates
scope of aryl iodides was investigated and shown in Table 2. Sub-
strates with functional groups such as methyl, ethyl, t-butyl, meth-
oxy, trifluoromethoxy, and 3,4-dimethyl group, gave the target
products in moderate to good yields (2b-2i). Halides groups includ-
ing fluoro, chloro, and 3-fluoro-4-methyl, furnished the corre-
sponding products in moderate yields (2k-2o). Examination of
electron-withdrawing substituents showed that slightly lower
yields were produced compared to electron-donating groups (2p,
2q). Heteroaryl groups such as 5-iodoindole, and 3-
iodothiophene could also successfully deliver the corresponding
products in 32% and 46% yields (2s, 2t). Moreover, biphenyl and
naphthalene substituents also gave the desired products in moder-
ate yields (2v, 2w).
Optimization of the reaction conditions.a
Entry Variation from the standard reaction conditions
Yield (%)
1
2
3
4
5
6
7
8
None
65 (64)
0
62
37, 21
0
0
Pd(OAc)2, Pd(dppp)Cl2, or [Ir(cod)Cl]2 as the catalyst
[Rh(cod)Cl]2 as the catalyst
Rh(nbd)2BF4 or [Rh(CO)2Cl]2 as the catalyst
Rh(PPh)3Cl as the catalyst
PPh3, PCy3, BuPAd2 instead of DPPP
DPPE, DPPB, Xanphos, DPPF, BINAP instead of DPPP 16, 0, 11, 46, 0
DPPP (6 mol%)
DPPP (12 mol%)
Et3N, DBU, DIPEA instead of Na2CO3
K2CO3, Li2CO3, Cs2CO3 instead of Na2CO3
NaHCO3, NaOH, Na3PO4 instead of Na2CO3
without 4 Å MS
38
58
0
0
56, 0, 21
55
58
9
10
11
12
13
14
extend the reaction time to 30 h
a
Reaction conditions: iodobenzene (1 mmol), HMF (1.2 mmol), Rh(cod)2BF4
(6 mol%), DPPP (9 mol%), Na2CO3 (1 mmol), 4 Å MS (150 mg), 2-methyltetrahydro-
furan (2.5 mL), 125 °C, 24 h. Yields were determined by GC with dodecane as an
internal standard. Yields of isolated products are given within parentheses.
DPPP = 1,3-bis(diphenylphosphino)propane;
ethane;
(diphenylphosphino)-9,9-dimethylxanthene; DPPF = 1,10-bis(diphenylphosphino)-
ferrocene; BuPAd2 = butyldi-1-adamantylphosphine; cod = 1,5-cyclooctadiene;
nbd = norbornadiene.
DPPE = 1,2-bis(diphenylphosphino)
Xanphos = 4,5-bis
DPPB = 1,4-bis(diphenylphosphino)butane;
ever, with monodentate phosphine ligands such as PPh3, PCy3 and
BuPAd2, HMF could hardly be converted, only furnishing biphenyl
as the main byproduct (Table 1, entry 6) [15]. This phenomena was
also observed when Rh(PPh3)3Cl was used as the catalyst (Table 1,
Subsequently, various alkyl iodides were examined as well
(Table 3). Gratifyingly, most of them were compatible with the
standard reaction conditions, and the corresponding products were
Table 2
Synthesis of furfuryl esters from aryl iodides.a
a
Reaction conditions: aryl iodides (1 mmol), HMF (1.2 mmol), Rh(cod)2BF4 (6 mol%), DPPP (9 mol%), Na2CO3 (1 mmol), 4 Å MS (150 mg), 2-
methyltetrahydrofuran (2.5 mL), 125 °C, 24 h, isolated yields. b135 °C. c115 °C.