Rhodium-catalyzed 1,4-addition of lithium 2-furyltriolborates to unsaturated ketones and esters for enantioselective synthesis of γ-oxo-carboxylic acids by oxidation of the furyl ring with ozone

Article abstract of DOI:10.1002/asia.201000589

Rhodium-catalyzed 1,4-addition of lithium 5-methyl-2-furyltriolborate ([ArB(OCH₂)₃CCH₃]Li, Ar=5-methyl-2-furyl) to unsaturated ketones to give β-furyl ketones was followed by ozonolysis of the furyl ring for enantioselecti

Full text of DOI:10.1002/asia.201000589

FULL PAPERS
DOI: 10.1002/asia.201000589
Rhodium-Catalyzed 1,4-Addition of Lithium 2-Furyltriolborates to
Unsaturated Ketones and Esters for Enantioselective Synthesis of g-Oxo-
Carboxylic Acids By Oxidation of the Furyl Ring with Ozone
Xiao-Qiang Yu, Tomohiko Shirai, Yasunori Yamamoto,* and Norio Miyaura[a]
Abstract: Rhodium-catalyzed 1,4-addi-
tion of lithium 5-methyl-2-furyltriolbo-
nylphosphino)-1,1’-binaphthyl (binap)
or 2,3-bis(diphenylphosphino)butane
(chiraphos) gave high yields and high
308C in a basic dioxane/water solution.
The corresponding reaction of unsatu-
rated esters, such as methyl crotonate,
had strong resistance under analogous
conditions, but the 1,4-adduct was ob-
tained in 70% yield and with 94% ee
when more electron-deficient phenyl
crotonate was used as the substrate.
rate ([ArB
N
methyl-2-furyl) to unsaturated ketones
to give b-furyl ketones was followed by
ozonolysis of the furyl ring for enantio-
selective synthesis of g-oxo-carboxylic
acids. [RhACHTUNGTRENNUNG(nbd)2]BF4 (nbd=2,5-norbor-
nadiene) chelated with 2,2’-bis(diphe-
selectivities in a range of 91–99% ee at
Keywords: 1,4-addition
·
asym-
metric synthesis · carboxylic acids ·
ketones · ozonolysis
Introduction
g-Oxo-carboxylic acids (3) are fragments that have been
used for the synthesis of various peptides, therapeutic
agents, and bioactive natural products.[1] A simple access to
such chiral carboxylic acids possessing a carbonyl group at
the g-carbon atom is enantioselective 1,4-addition of nucleo-
philes equivalent to a hydroxycarbonyl group (2 [Eq. (1)]).
Masked nucleophiles for such unavailable HO(O=)CÀ
anions are cyanide ions (2a),[2–4] carbanions stabilized by ad-
jacent sulfur atoms (2b),[5] 2-oxazole[6] or 2-imidazole[7]
anions (2c), and 2-furyl anions (2d).[8] Among these tradi-
tional synthons, there have been extensive studies on cata-
lyzed enantioselective cyanation of unsaturated carbonyl
compounds,[3,4] but there has been little use of other chiral
protocols.[9]
RuCl3/NaIO4 (Scheme 1). Furyl rings are excellent synthons
of the hydroxycarbonyl group that allow various syntheses
of amino acids, pyrrolidine carboxylic acids, and g-keto
esters.[8] However, attempts at arylation of enones with het-
eroarylboronic acids, such as 2-furylboronic acids, were un-
À
À
successful because of competitive C B bond cleavage of C
B bonds with water relative to 1,4-addition to unsaturated
carbonyl compounds.[11] The instability of 2-heteroarylboron-
ic acids is known to cause readily protodeboronation in
aqueous media.[11b] This is attributable to the high coordina-
tion ability of heteroatoms to catalysts and slow transmeta-
lation and insertion of electron-deficient heteroaryl rings.
Thus, we recently developed tetracoordinated ate-complexes
of boronic esters, namely organotriolborate salts, for metal-
catalyzed reactions in nonaqueous media.[12] 1,4-Additions
As part of our program to develop catalyzed reactions of
organoboronic acids with rhodium or palladium catalysts,[10]
we wish to report enantioselective arylation of enones with
2-furyltriolborates to give b-furyl ketones and their conver-
sions into caraboxylic acids by oxidation with ozone or
[a] Dr. X.-Q. Yu, T. Shirai, Dr. Y. Yamamoto, Prof. Dr. N. Miyaura
Division of Chemical Process Engineering
Graduate School of Engineering
of pyridyl- and thiophenylACTHNURTGNEU(GN triol)borates to unsaturated car-
Hokkaido University
N13, W8, Sapporo 060-8628 (Japan)
Fax : (+81)11-706-6560
bonyl compounds resulted in high yields and high enantiose-
lectivities, up to 97% ee in the presence of rhodium cata-
lysts.[13] To our delight, furyl analogues (5) were found to
E-mail: yasuyama@eng.hokudai.ac.jp
932
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 932 – 937

Results and Discussion
Synthesis of 2-furyltriolborates
The azeotropic removal of water from a stoichiometric mix-
ture of organoboronic acids and 1,1,1-tris(hydroxymethyl)-
ethane (triol) or alkylation of BACHTNUGRTENUNG(OiPr)3 with aryllithiums fol-
lowed by ester exchange with triol gives triolborates. The
latter procedure is convenient for the synthesis of lithium
salts of 2-furylborates (5a–d) [Eq. (2)]. 5-Methyl-2-furylbor-
onate (5b) was obtained in quantitative yield as an air-
stable white solid.
Reaction conditions: Initially, we chose 2-cyclohexenone
(4b) to optimize chiral ligands and substituents on the furyl
rings of lithium 2-furyltriolborates (5) (Table 1). The reac-
tion was carried out in dioxane/H2O (16:1) at 308C for
Table 1. Reaction conditions.[a]
Entry
5
Chiral ligand
9
Yield [%][b]
ee [%][c]
1
2
3
4
5
6
7
8
5a
5b
5b
5b
5b
5b
5b
5c
5d
6
(S)-binap
(S)-binap
(S)-tol-binap
ACHTUNGTREN(NGNU S,S)-chiraphos
(R)-Me-bipam
(R)-N-Me-bipam
(R)-difluorphos
(S)-binap
(S)-binap
(S)-binap
9ba
9bb
9bb
9bb
9bb
9bb
9bb
9bc
9bd
9bb
9bb
9bb
61
82
60
87
60
39
78
52
43
0
95
98
98
93
96
71
98
94
93
–
Scheme 1. Asymmetric synthesis of g-oxo-carboxylic acids by 1,4-addition
of lithium 2-furanyltriolborate to a,b-unsaturated carbonyl compounds.
9
10
11
12
7
8
(S)-binap
(S)-binap
trace
0
–
–
have much more resistance to protonolysis than thiophenyl-
or pyridylborates to arylate cyclic and acyclic enones (4).
The reaction took place smoothly at 308C when a catalytic
amount of K2CO3 (10%) was used in aqueous dioxane.
[a] A mixture of 2-cyclohexenone (4b, 0.5 mmol), lithium 2-furyl triolbo-
rates (5, 1.25 mmol), and K2CO3 (0.1 mmol) was stirred at 308C for 20 h
in the presence of [RhACHTUNGRTNEUNG(nbd)2]BF4 (3 mol%) and chiral ligand (3.3 mol%)
in dioxane/H2O (16:1, 3.2:0.2 mL). [b] Isolated yields of 9 determined by
chromatography. [c] Enantiomeric excess determined by chiral stationary
columns.
Abstract in Japanese:
20 hours in the presence of K2CO3 (10 mol%) and 5–8
(2.5 equiv). The catalyst was prepared in situ by mixing [Rh-
AHCTUNTGRENGUN(N nbd)2]BF4 (3 mol%; nbd=2,5-norbornadiene and (S)-binap
(3.3 mol%). Although the reaction occured at 958C under
conditions analogous to those for pyridylborates in dry diox-
ane,[13] the presence of a base and water was advantageous
for lowering the reaction temperature and improving the
enantioselectivities. [RhACHTNUTRGNE(UNG nbd)2]BF4 and binap (2,2’-bis(di-
phenylphosphino)-1,1’-binaphthyl; Table 1, entry 2) or di-
fluorphos (5,5’-bis(diphenylphosphino)-2,2,2’,2’-tetrafluoro-
4,4’-bi-1,3-benzodioxole; entry 7) were found to be the best
Chem. Asian J. 2011, 6, 932 – 937
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
933

Y. Yamamoto et al.
FULL PAPERS
combination for 2-cyclohexenone among the representative
chiral ligands previously used for such addition reactions,
such as tol-binap,[14] Me-bipam (bidentate phosphoramidite)
and N-Me-bipam.[12,15] On the other hand, substituents on
the furyl ring (R3) affected both the yields and enantioselec-
tivities. The best selectivity for the binap catalyst was ob-
tained with 5-methylfurylborate (5b) (entry 2), whereas me-
thoxyfuryl (5c), benzofuryl (5d), and an unsubstituted one
(5a) resulted in lower selectivities than to that of 5b. Fu-
thermore, no desired product was obtained with boronic
acid (6), pinacol ester derivative (7), and potassium trifluor-
oborate (8).[16]
at increasing the chemical yield were unsuccessful. The furyl
rings thus synthesized are excellent synthons of a carboxylic
acid group in various syntheses of carboxylic acids.[8] Ozone
is used for the oxidation of the furyl rings because a combi-
nation of RuCl3 and NaIO4 resulted in a complex mixture of
several produts. Thus, ozonolysis of 9ab–cb in methanol
smoothly occurred at À788C to yield 3-keto-cycloalkanecar-
boxylic acids (10a–c) in 75–87% yields (entries 1–4). Analo-
gously, acyclic compounds 9db–9gb gave the corresponding
chiral carboxylic acids 10d–g in high yields without produc-
ing a byproduct and with no racemization of their stereo-
chemistry (entries 2–6, 8, and 9).
Scope and limitations: Lithium 5-methyl-2-furanyltriolbo-
rate (5b) was smoothly added to five-, six-, and seven-mem-
bered unsaturated ketones in good yields and with excellent
enantiomeric excess under the optimized conditions
(Table 2, entries 1–4). A difluorphos complex resulted in
Conclusions
We have demonstrated a two-step synthesis of chiral g-oxo-
carboxylic acids and high efficiency of lithium triolborates
for enantioselective 1,4-addition
of furyl groups to a,b-unsatu-
Table 2. Synthesis of chiral g-keto-carboxylic acids (7) by an asymmetric 1,4-addition/oxidation sequence.[a]
rated carbonyl compounds with
chiral rhodium catalysts. As g-
oxo-carboxylic acids are versa-
tile synthetic intermediates for
further transformations, the
methodology should have great
potential in organic synthesis,
particularly in the context of
stereoselective synthesis of bio-
logically active target molecules
in natural product and pharma-
Entry
4
Chiral ligand
9
Yield [%][b]
ee [%][c]
10
Yield [%][b]
ee [%][d]
1
4a
4a
4b
4c
4d
4e
4 f
4 f
4g
4h
4i
(S)-binap
(R)-difluorphos
(S)-binap
(S)-binap
(S)-binap
(S)-binap
(S)-binap
(S,S)-chiraphos
(S)-binap
(S)-binap
9ab
9ab
9bb
9cb
9 db
9eb
9 fb
9 fb
9gb
9hb
9ib
92
71
82
65
90
79
35
83
86
70
51
91
95
95
95
99
99
96
91
92
94
82
10a
10a
10b
10c
10d
10e
–
10 f
10g
–
85
85
87
83
91
85
–
91
88
–
n.d.
95 (R)
93 (S)
94
97
99
2[e]
3
4
5
6
7
–
8[f]
9
90 (S)
91
–
10
11[g]
A
–
–
–
[a] A mixture of unsaturated carbonyl compound (4, 0.5 mmol), lithium 5-methyl-2-furyl triolborates (5b, ceutical research areas.
1.25 mmol), K2CO3 (0.1 mmol), [Rh(nbd)2]BF4 (3 mol%), and chiral ligand (3.3 mol%) in dioxane/H2O (16:1,
AHCTUNGTRENNUNG
3.2:0.2 mL) was stirred at 308C for 20 h to prepare 9. Ozone was then bubbled for 30 min into a solution of 9
in MeOH at À788C to give 10. [b] Isolated yields determined by chromatography. [c] The enantiomeric excess
was determined by chiral stationary columns. [d] The enantiomeric excess was determined by chiral stationary
columns or chiral GC after esterification of carboxylic acids. The letter within the parentheses indicates the ab-
Experimental Section
General: IR spectra were recorded on
solute configuration of the chiral center within the product. [e] [Rh
ACHTUNGTERN(NUNG nbd)2]BF4/difluorphos (5:5.5 mol%) was
a
Thermo Nicolet AVATAR 320
used at 508C. [f] [Rh(nbd)2]BF4/chiraphos (5:5.5 mol%) was used at 508C. [g] The reaction was carried out in
ACHTUNGTRENNUNG
FTIR. Wavelength of maximum ab-
dioxane at 1008C for 20 h. n.d.=Not determined.
sorbance is quoted in cmÀ1
spectra were recorded on
.
1H NMR
JEOL
a
JNM-400II (400 MHz) in CDCl3 (dH =
7.25 ppm) with tetramethylsilane as an internal standard. Chemical shifts
are reported in parts per million (ppm) and signals are expressed as sin-
glet (s), doublet (d), triplet (t), quartet (q), multiplet (m), and broad (br).
13C NMR spectra were recorded on a JEOL JNM-400II (100 MHz) in
CDCl3 (dC =77.0 ppm) with tetramethylsilane as an internal standard.
Chemical shifts are reported in parts per million (ppm). HPLC analysis
was directly performed on a chiral stationary phase column, Chiralcel
OD-H, AD, AD-H, OJ-H, and OB-H purchased from Diacel. GC analy-
sis was performed on HITACHI G-7000 on a Varian Chirasil DEX CB
column and ASTEC CHIRALDEX G-TA column. HRMS spectra were
recorded on JEOL JMS AX-500 or JEOL JMS-SX102A mass spectrome-
ters at the Center for Instrumental Analysis, Hokkaido University. Opti-
cal rotations were measured on a HORIBA SEPA-300 digital polarime-
higher selectivites than the binap complex for cyclopente-
none (entry 2). High yields and high selectivities were also
obtained for an acyclic ketone posessing a primary and sec-
ondary alkyl substituent at the b-carbon (4d, 4e, entries 5
and 6), whereas a 2,3-bis(diphenylphosphino)butane (chira-
phos) complex resulted in better yields than those of binap
for 4-phenyl-2-butanone (4 f, entries 7 and 8). Such high effi-
ciency of a chiraphos ligand for ketone and ester substrates
containing an aryl group at the b-carbon atom has been
demonstrated in the palladium- and rhodium-catalyzed 1,4-
addition of arylboronic acids.[17,18] The addition to typical un-
saturated esters, such as methyl crotonate, was very slow,
but electron-deficient phenyl crotonate (4h) gave the 1,4-
adduct in 70% yield with 94% ee (entry 10).[16d] Again, ary-
lation of coumarin (4i) failed with the binap catalyst, but
82% ee was achieved when (S,S)-chiraphos was used as the
chiral auxiliary at 1008C (entry 11). However, all attempts
ter. Kanto Chemical silica gel (60, particle size 0.063–0.210 mm) was used
[19]
for flash column chromatography. [Rh
ACHTUGNTREN(NUNG nbd)2]BF4, was prepared by the
literature procedure. [RhOHACTHNUGTRNEUN(G cod)]2 (cod=1,5-cyclooctadiene) was com-
mercially available from Aldrich. 1,4-Dioxane was purchased from Wako.
Lithium 5-methyl-2-furanyl triolborate (5b): Lithium 5-methyl-2-furanyl
triolborate (5b) was prepared by the literature procedure.[12] tBuLi
(100 mmol) in pentane was added to a stirred solution of 2-methylfuran
934
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Chem. Asian J. 2011, 6, 932 – 937

Rhodium-Catalyzed 1,4-Addition of Lithium 2-Furyltriolborates
(100 mmol) in tetrahydrofuran (THF; 300 mL) at À788C. The resulting
mixture was stirred for 2 h at À408C, and then a solution of triisopropyl
borate (110 mmol) was added. The mixture was stirred for 1 h at À788C
and then allowed to warm to room temperature. A solution of 1,1,1-
tris(hydroxymethyl)ethane (100 mmol) in THF (150 mL) was then added
and the resulting mixture was stirred for 5 h. Concentration to dryness
under reduced pressure gave 5b (82%).
13.4 ppm; IR (neat): n˜ =2925, 1710, 1577, 1503, 795 cmÀ1; [a]D20 =À3.5
(c=1.00 in CHCl3); HPLC (OJ-H, 25% iPrOH in hexane, 0.5 mLminÀ1
,
254 nm): tminor =8.1, tmajor =9.5 min; 99% ee; HRMS (EI): m/z: calcd for
C12H18O2: 194.1307 [M]+; found 194.1300.
4-(5-Methyl-2-furanyl)-4-phenyl-2-butanone (9 fb): 1H NMR (400 MHz,
CDCl3): d=7.21–7.31ACTHNUTRGNEUNG(m, 5H), 5.85 (d, J=2.9 Hz, 1H), 5.83 (d, J=
3.4 Hz, 1H), 4.53 (t, J=7.3 Hz, 1H), 3.20 (dd, J=16.6, 7.3 Hz, 1H), 2.97
(dd, J=16.6, 7.3 Hz, 1H), 2.22 (s, 3H), 2.09 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=206.4, 154.6, 151.1, 141.9, 128.5, 127.7, 126.8,
106.3, 105.9, 48.6, 40.3, 30.4, 13.5 ppm; IR (neat): n˜ =2935, 1700, 1558,
1501, 1471, 796 cmÀ1; [a]D20 =À11.3 (c=1.00 in CHCl3); HPLC (OD-H,
Typical procedure for rhodium-catalyzed asymmetric conjugate additions
of lithium 2-furyl triolborates to a,b-unsaturated carbonyl compounds:
Lithium
2-furyl
triolborate
(5a;
1.25 mmol),
[RhACTHUNGTERNNU(G nbd)2]BF4
(0.015 mmol), and (S)-binap (0.0165 mmol) or (S,S)-chiraphos
(0.0165 mmol) were added to a 10 mL flask containing a magnetic stir-
ring bar, a septum inlet, and a reflux condenser. The flask was flashed
with argon and charged with 1,4-dioxane/H2O (3.2:0.2 mL), and then the
mixture was stirred for 30 min at room temperature. After addition of an
unsaturated carbonyl compound (0.5 mmol), the mixture was stirred for
16–20 h at 308C. The reaction was quenched with NH4Cl (sat.) for 0.5 h.
The product was extracted with ethyl acetate (3ꢁ5 mL), washed with
brine, and dried over anhydrous MgSO4. The desired product was puri-
fied by column chromatography on silica gel.
10% EtOH in hexane, 0.5 mLminÀ1
, 254 nm): tmajor =11.7, tminor =
12.9 min; 91% ee; HRMS (EI): m/z: calcd for C15H16O2: 228.1150 [M]+;
found 228.1149.
3-(5-Methyl-2-furanyl)-1-phenyl-1-butanone (9gb): 1H NMR (400 MHz,
CDCl3): d=7.94–7.97 (m, 2H), 7.53–7.57 (m,1H), 7.45 (t, J=7.8 Hz, 2H),
5.88 (d, J=2.9 Hz, 1H), 5.83 (d, J=2.9 Hz, 1H), 3.50–3.54 (m, 1H), 3.40
(dd, J=16.6, 4.3 Hz, 1H), 3.05 (dd, J=16.6, 8.8 Hz, 1H), 2.23 (s, 3H),
1.30 ppm (d, J=6.88 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=198.8,
157.4, 150.4, 137.1, 133.0, 128.5, 128.1, 105.7, 104.4, 44.4, 29.3, 18.9,
The spectra of compounds 9ba,[11d–e,20] 9bb,[21] 9bd,[11e,20] 9ab,[11e,21,22]
9cb,[21] 10a,[23] 10b,[9a,23h,24] 10c,[25] 10d,[26] 10 f,[27] and 10g[1c–d,9b,28] were
identical to those reported in the literature.
13.5 ppm; IR (neat): n˜ =2930, 1703, 1560, 1508, 1455, 798 cmÀ1; [a]D20
=
À18.6 (c=1.00 in CHCl3); HPLC (IA, 0.2% iPrOH in hexane,
0.5 mLminÀ1, 254 nm): tminor =25.7, tmajor =29.6 min; 92% ee; HRMS (EI):
m/z: calcd for C15H16O2: 228.1150 [M]+; found 228.1148.
3-(5-Methyl-2-furanyl)cyclopentanone (9ab):[11e,21,22] 1H NMR (400 MHz,
CDCl3): d=5.91 (d, J=2.8 Hz, 1H), 5.85 (d, J=2.8 Hz, 1H), 3.45–3.41
(m, 1H), 2.56 (dd, J=18.3, 7.5 Hz, 1H), 2.42–2.30 (m, 3H), 2.27–2.23 (m,
1H), 2.25 (s, 3H), 2.13–2.05 ppm (m, 1H); 13C NMR (100 MHz, CDCl3):
Phenyl 3-(5-methyl-2-furanyl) butanoate (9hb): 1H NMR (400 MHz,
CDCl3): d=7.34–7.38 (m, 2H), 7.21 (t, J=7.3 Hz, 1H), 7.03–7.06 (m,
2H), 5.94 (d, J=2.7 Hz, 1H), 5.87 (d, J=1.8 Hz, 1H), 3.39–3.48 (m, 1H),
2.93 (dd, J=15.1, 6.8 Hz, 1H), 2.69 (dd, J=15.1, 7.8 Hz, 1H), 2.26 (s,
3H), 1.37 ppm (d, J=7.3 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=
170.8, 156.5, 150.9, 150.8, 129.5, 125.9, 121.7, 105.9, 104.9, 40.8, 30.4, 19.0,
13.7 ppm; IR (neat): n˜ =2975, 1733, 1501, 800 cmÀ1; [a]D20 =À40.1 (c=1.00
d=218.3, 154.8, 151.2, 105.9, 105.3, 43.8, 37.9, 35.6, 28.7, 13.6 ppm; [a]D21
+27.3 (c=4.00 in CHCl3); 95% ee.
=
3-(5-Methyl-2-furanyl)cyclohexanone (9bb):[21] 1H NMR (400 MHz,
CDCl3): d=5.87 (d, J=2.9 Hz, 1H), 5.84 (d, J=2.9 Hz, 1H), 3.12–3.09
(m, 1H), 2.68–2.62 (m, 1H), 2.53–2.47 (m, 1H), 2.41–2.26 (m, 2H), 2.24
(s, 3H), 2.15–2.11 (m, 1H), 2.05–1.99 (m, 1H), 1.85–1.75 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=210.6, 155.5, 150.9, 105.9, 105.1, 45.9,
41.4, 37.8, 30.1, 245, 13.6 ppm; [a]1D9 =+39.1 (c=4.00 in CHCl3); 95% ee.
in CHCl3); HPLC (OD-H, 0.5% iPrOH in hexane, 0.5 mLminÀ1
,
254 nm): tmajor =18.3, tminor =20.0 min; 94% ee; HRMS (EI): m/z: calcd
for C15H16O3: 244.1099 [M]+; found 244.1097.
4-(5-Methyl-2-furanyl)-3,4-dihydro-2-chromenone
(9ib):
1H NMR
3-(5-Methoxy-2-furanyl)cyclohexanone (9bc): 1H NMR (400 MHz,
CDCl3): d=5.86 (d, J=1.0 Hz, 1H), 5.12 (d, J=1.0 Hz, 1H), 3.05–3.12
(m, 1H), 2.60–2.65 (m, 1H), 2.46–2.52 (m, 1H), 2.33–2.39 (m, 2H), 2.09–
2.12 (m, 1H), 1.98–2.03 (m, 1H), 1.71–1.86 ppm (m, 2H); 13C NMR
(100 MHz, CDCl3): d=210.5, 146.8, 115.3, 105.5, 79.2, 57.6, 45.4, 41.2,
(400 MHz, CDCl3): d=7.08–7.30 (m,4H), 5.89 (d, J=2.9 Hz, 1H), 5.86
(d, J=2.9 Hz, 1H), 4.33 (t, J=6.4 Hz, 1H), 3.18 (dd, J=6.4, 16.1 Hz,
1H), 2.99 (dd, J=5.9, 16.1 Hz, 1H), 2.24 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=167.4, 152.4, 151.4, 150.8, 129.0, 128.2, 124.6,
123.5, 117.2, 107.7, 106.2, 34.8, 34.0, 13.5 ppm; IR (neat): n˜ =2978, 1726,
1493, 1328, 1106, 830 cmÀ1; [a]D20 =À1.9 (c=1.00 in CHCl3); HPLC (OJ-
37.4, 29.8, 24.2 ppm; IR (neat): n˜ =2928, 1713, 1579, 1508, 1456, 798 cmÀ1
;
H, 0.5% iPrOH in hexane, 0.5 mLminÀ1, 230 nm): tmajor =15.9, tminor
=
[a]2D0 =À29.6 (c=1.00 in CHCl3); HPLC (AD-H, 1% iPrOH in hexane,
0.5 mLminÀ1, 230 nm): tminor =21.5, tmajor =24.1 min; 94% ee; HRMS (EI):
m/z: calcd for C12H15NO2: 194.0943 [M]+; found 194.0951.
18.4 min; 82% ee; HRMS (EI): m/z: calcd for C14H12O3: 228.0786 [M]+;
found 228.0790.
3-(5-Methyl-2-furanyl)cycloheptanone (9cb):[21] 1H NMR (CDCl3): d=
5.84 (d, J=3 Hz, 1H), 5.82 (d, J=3 Hz, 1H), 3.03–2.97 (m, 1H), 2.82–
2.76 (m, 2H), 2.53 (dd, J=7.7, 4.5 Hz, 2H), 2.27–2.17 (m, 1H), 2.23 (s,
3H), 2.01–1.88 (m, 2H), 1.73–1.50 ppm (m, 3H); 13C NMR (CDCl3): d=
213.4, 156.5, 150.7, 105.8, 104.5, 48.3, 44.1, 35.8, 35.7, 28.7, 24.2, 13.6 ppm;
[a]2D0 =À23.2 (c=4.8 in CHCl3); 95% ee; HRMS (EI): m/z: calcd for
C12H16O2: 192.1150 [M]+; found 192.1148.
4-(5-Methyl-2-furanyl)-2-nonanone (9db): 1H NMR (400 MHz, CDCl3):
d=5.85 (d, J=2.9 Hz, 1H), 5.12 (d, J=1.0 Hz, 1H), 3.14–3.20 (m, 1H),
2.75 (dd, J=16.1, 7.3 Hz, 1H), 2.61 (dd, J=16.1, 6.8 Hz, 1H), 2.23 (s,
3H), 2.08 (s, 3H), 1.47–1.59 (m, 2H), 1.21–1.26 (m ,6H), 0.85 ppm (t, J=
6.88 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=207.8, 155.7, 150.46,
105.7, 105.6, 48.1, 34.6, 33.9, 31.6, 30.4, 26.8, 22.5, 14.0, 13.5 ppm; IR
(neat): n˜ =2930, 1709, 1580, 1499, 1453, 799 cmÀ1; [a]D20 =À28.9 (c=1.00
in CHCl3); HPLC (AS-H, 10% iPrOH in hexane, 0.5 mLminÀ1, 254 nm):
Typical procedure for ozonolysis: The present furylation product (9) was
dissolved in methanol and the solution was cooled to À788C. Ozone gas
was passed through the solution. After 30 min, the reaction was stopped
and oxygen was passed through the mixture to remove the excess ozone.
The reaction mixture was allowed to warm to RT and then stirred for
10 min. The mixture was eluted with Et2O until the product could no
longer be detected (TLC). The filtrate was then concentrated in vacuo
and the residue dissolved in NaOH (1m, 5 mL) and washed with Et2O
(25 mL). The aqueous phase was acidified with HCl (2n) and extracted
with ethyl acetate (5ꢁ5 mL). The combined organic layers were dried
(MgSO4) and concentrated.
(R)-3-Oxocyclopentanecarboxylic acid (10a):[23] Yield: 85%; 1H NMR
(400 MHz, CDCl3): d=10.46 (brs, 1H), 3.18 (m, 1H), 2.58–2.16 ppm (m,
6H); 13C NMR (100 MHz, CDCl3): d=216.8, 180.3, 40.9, 40.8, 37.3,
26.4 ppm.
1
t
major =8.8, tminor =9.3 min; 99% ee; HRMS (EI): m/z: calcd for C14H22O2:
(S)-3-Oxocyclohexanecarboxylic acid (10b):[9a,23h,24] Yield: 87%; H NMR
222.1620 [M]+; found 222.1618.
(400 MHZ, CDCl3): d=9.23 (brs, 1H), 2.91–2.84 (m, 1H), 2.58–2.56 (m,
2H), 2.44–2.37 (m, 2H), 2.36–2.06 (m, 2H), 1.94–1.72 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=209.4, 179.4, 42.8, 42.6, 40.8, 27.4,
24.3 ppm; the absolute configuration was determined by comparing the
optical rotation to the reported value.
3-Oxocycloheptanecarboxylic acid (10c):[25] Yield: 83%; 1H NMR
(400 MHz, CDCl3): d=9.31 (brs, 1H), 2.91–2.84 (m, 1H), 2.59–1.76 ppm
5-Methyl-4-(5-methyl-2-furanyl)-2-hexanone (9eb): 1H NMR (400 MHz,
CDCl3): d=5.84 (d, J=2.9 Hz, 1H), 5.81 (d, J=2.9 Hz, 1H), 3.07 (tt, J=
10.8, 5.6 Hz, 1H)), 2.79 (dd, J=16.1, 7.2 Hz, 1H), 2.62 (dd, J=16.1,
5.3 Hz, 1H), 2.23 (s, 3H), 2.07 (s, 3H), 1.83–1.92 (m, 1H), 0.88 (d, J=
6.8 Hz, 1H), 0.82 ppm (d, J=6.8 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d=207.9, 154.5, 150.2, 106.5, 105.6, 44.7, 40.8, 31.6, 30.2, 20.2, 19.5,
Chem. Asian J. 2011, 6, 932 – 937
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
935

Y. Yamamoto et al.
FULL PAPERS
(m, 10H); 13C NMR (100 MHz, CDCl3): d=209.9, 179.4, 42.8, 42.6, 40.7,
32.7, 27.4, 24.2 ppm.
0.92 (d, J=6.80 Hz, 3H), 0.90 ppm (d, J=6.80 Hz, 3H); 13C NMR
(100 MHz, CDCl3): d=207.4, 175.3, 51.6, 46.3, 42.0, 30.2, 30.0, 20.2,
19.7 ppm; [a]2D3 =+21.2 (c=0.5 in CHCl3); HPLC (IB, 10% iPrOH in
2-(2-Oxopropyl)heptanoic acid (10d):[26] Yield: 91%; 1H NMR
(400 MHz, CDCl3): d=10.8 (brs, 1H), 2.83–2.81 (m, 2H), 2.49–2.44 (m,
1H), 2.10 (s, 3H), 1.59–1.40 (m, 2H), 1.30–1.22 (m, 6H), 0.81 ppm (t, J=
6.83 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=207.0, 181.4, 44.5, 39.9,
31.5, 31.4, 29.8, 26.5, 22.3, 13.9 ppm.
2-Isopropyl-4-oxopentanoic acid (10e): Yield: 85%; 1H NMR (400 MHz,
CDCl3): d=2.90–2.80 (m, 2H), 2.46 (s, 1H), 2.42 (s, 1H), 2.11 (s, 3H),
2.09–2.03 (m, 1H), 0.97 (d, J=6.83 Hz, 3H), 0.94 ppm (d, J=6.83 Hz,
3H); 13C NMR (100 MHz, CDCl3): d=207.3, 180.4, 46.0, 41.2, 30.0, 29.6,
20.2, 19.3 ppm.
4-Oxo-2-phenylpentanoic acid (10 f):[27] Yield: 91%; the spectra of the
compound were identical to those reported in the literature.
2-Methyl-4-oxo-4-phenylbutanoic acid (10g):[1c–d, 9b,28] Yield: 88%;
1H NMR (400 MHz, CDCl3): d=7.97 (m, 2H), 7.95–7.44 (m, 3H), 3.47
(dd, J=17.5, 7.81 Hz, 1H), 3.18–3.13 (m, 1H), 3.05 (dd, J=17.5, 5.4 Hz,
1H), 1.32 ppm (d, J=7.31 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=
197.8, 182.2, 136.4, 133.3, 130.1, 128.6, 128.04, 128.0, 41.6, 34.8, 17.0 ppm.
hexane, 0.5 mLminÀ1
, 254 nm): tminor =7.2, tmajor =8.6 min; 99% ee;
HRMS (EI): m/z: calcd for C8H13O3: 157.08647 [MÀCH3]; found
157.08655.
Methyl 4-oxo-2-phenylpentanoate:[27] Yield: 78%; 1H NMR(400 MHz,
CDCl3): d=7.34–7.25 (m, 5H), 4.11 (dd, J=4.08, 10.4 Hz, 1H), 3.66 (s,
3H), 3.40 (dd, J=10.4, 18.1 Hz, 1H), 2.72 (dd, J=4.08, 18.1 Hz, 1H),
2.18 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=206.35, 173.84,
138.18, 128.97, 127.80, 127.62, 52.42, 47.19, 46.17, 30.06 ppm; [a]D19
=
+137.8 (c=3.6 in CHCl3); HPLC (OJ, 2% iPrOH in hexane, flow=
1.0 mLminÀ1, 254 nm): tmajor =35.8, tminor =39.8 min; 90% ee; HRMS (EI):
m/z: calcd for C12H14O3: 206.09429 [M]+; found 206.09415.
Methyl 2-methyl-4-oxo-4-phenylbutanoate:[33] Yield: 78%; 1H NMR
(400 MHz, CDCl3): d=7.96–7.94 (m, 2H), 7.57–7.43 (m, 3H), 3.69 (s,
3H), 3.50–3.44 (m, 1H), 3.15–2.99 (m, 2H), 1.27 ppm (d, J=7.36 Hz,
3H); 13C NMR (100 MHz, CDCl3): d=198.1, 176.6, 136.7, 133.3, 128.7,
128.1, 52.0, 42.1, 34.9, 17.4 ppm; [a]2D2 =+19.4 (c=2.6 in CHCl3); HPLC
(AD-H, 10% iPrOH in hexane, 0.5 mLminÀ1
,
254 nm):
t
minor =13.9,
Esterification of carboxylic acids
t
major =14.8 min; 91% ee; HRMS (EI): m/z: calcd for C12H14O3: 206.09429
[M]+; found 206.09391.
Method A:[29] Acid was dissolved in methanol and Amberlyst-15 (10%
w/w) was added to the solution. The reaction mixture was refluxed for
5 h. The resin was filtered off thorugh a glass filter and extracted with
ethyl acetate, dried over MgSO4, and concentrated in vacuo. The residue
was purified by column chromatography on silica gel.
Acknowledgements
Methyl 3,3-dimethoxycyclohexanecarboxylate:[4c] Yield: 82%; 1H NMR
(400 MHz, CDCl3): d=3.65 (s, 3H), 3.19 (s, 3H), 3.13 (s, 3H), 2.45–2.54
(m, 1H), 2.20–2.25 (m, 1H), 1.90–2.00 (m, 2H), 1.66–1.72 (m, 1H), 1.21–
1.48 ppm (m, 4H); 13C NMR (100 MHz, CDCl3): d=175.9, 99.7, 51.7,
47.7, 47.5, 40.1, 35.1, 31.9, 28.3, 21.8 ppm; [a]2D3 =+11.8 (c=1.9 in
CHCl3); Chiral GC (DEX-CB, injector T=2008C, detector T=2508C,
This work was supported by a Grant-in-Aid for Science Research on Pri-
ority Areas (no. 18064001, Synergy of Elements) and the global COE
program (no. B01, Catalysis as the Basis for the Innovation in Materials
Science) from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
column T=1008C (isothermic), flow=0.5 mLminÀ1): tminor =15.5, tmajor
=
16.0 min; 93% ee; HRMS (EI): m/z: calcd for C10H18O4: 202.12051 [M]+;
found 202.12084.
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2H), 2.19–1.47 ppm (m, 6H); 13C NMR (100 MHz, CDCl3): d=212.2,
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T=1108C (isothermic), flow=1.5 mLminÀ1): tminor =10.1, tmajor =10.7 min;
94% ee; HRMS (EI): m/z: calcd for C9H14O3: 170.09429 [M]+; found
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Method B: Acid was dissolved in H2SO4/methanol and refluxed for 1 h.
The mixture was extracted with ethyl acetate. The combined organic
layers were washed with saturated aqueous NaHCO3, dried over MgSO4,
and concentrated in vacuo. The residue was purified by column chroma-
tography on silica gel.
Methyl 3-oxocyclopentanonecarboxylate:[23f,31] Yield: 82%; 1H NMR
(400 MHz, CDCl3): d=3.68 (s, 3H), 3.09 (quin., J=6.8 Hz, 1H), 2.50–
2.06 ppm (m, 6H); 13C NMR (100 MHz, CDCl3): d=216.65, 174.79,
52.22, 41.22, 40.83, 37.50, 26.63 ppm; [a]2D0 =+37.0 (c=3.5 in CHCl3);
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2508C, column T=1008C (isothermic), flow=1.0 mLminÀ1, tminor =14.7,
t
major =15.3 min, 95% ee; HRMS m/z: calcd for C7H10O3: 142.06299 [M]+;
found 142.06301.
Methyl 2-(2-oxopropyl)heptanoate: Yield: 70%; 1H NMR (400 MHz,
CDCl3): d=3.66 (s, 3H), 2.89–2.81 (m, 2H), 2.52–2.44 (m, 1H), 2.14 (s,
3H), 1.60–1.41 (m, 2H), 1.30–1.22 (m, 6H), 0.86 ppm (t, J=7.33 Hz,
3H); 13C NMR (100 MHz, CDCl3): d=207.02, 176.10, 51.81, 45.13, 40.08,
31.97, 31.64, 30.10, 26.75, 22.50, 14.05 ppm; [a]2D2 =+22.9 (c=3.6 in
CHCl3); HPLC (OB-H, 10% iPrOH in hexane, 0.5 mLminÀ1, 254 nm):
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1
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Received: August 19, 2010
Published online: January 4, 2011
Chem. Asian J. 2011, 6, 932 – 937
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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