Triphenylphosphine-mediated reduction of electron-deficient propargyl ethers to the allylic ethers

Article abstract of DOI:10.1002/jccs.200100126

Semihydrogenation of α,β-unsaturated ynoates and -ynones bearing a γ-alkoxy group can be performed using triphenylphosphine and water. α,β-Unsaturated ynoates were reduced to a mixture of cis and trans α,β-unsaturated enoates, whereas, ynones were reduced to trans α,β-unsaturated enones as the only products.

Full text of DOI:10.1002/jccs.200100126

JournaloftheChineseChemicalSociety, 2001, 48, 869-876
869
Triphenylphosphine-Mediated Reduction of Electron-DeficientPropargyl
Ethers to the Al lyl ic Ethers
Ming-Shan Tsai (
), U. Narasimha Rao (
), Jeng-Rong Wang (
),
Chung-Hao Liang (
) and Ming-Chang P. Yeh* (
)
DepartmentofChemistry,NationalTaiwanNormalUniversity,Taipei117,Taiwan,R.O.C.
Semihydrogenation of , -unsaturatedynoatesand-ynonesbearinga -alkoxy group can be per formed
us ing triphenylphosphine and wa ter. , -Un sat u rated ynoates were re duced to a mix ture ofcis and trans
, -unsaturatedenoates,whereas,ynoneswerereducedtotrans , -unsaturatedenonesastheonlyproducts.
INTRODUCTION
Of the many methods avail able for re duc tion of al-
(cis -2a/trans-2a = 2.8/1) in 79% yield af ter aque ous quench-
ing and flash col umn chro ma tog ra phy on sil ica gel (en try 1,
Table1).Inanefforttoacceleratethisprocess,weconsidered
the use of a 2.0 mo lar equiv of triphenylphosphine. Thus, the
reactionof1a with triphenylphosphine (2.0 equiv) in to lu ene
at 5 C gen er ated within 2 h the cis-2a and trans-2a with the
similarcis/transratioandisolatedyield.Various , -unsatu-
rated ynoates1b-e were re duced tocis- andtrans , -unsatu-
rated enoates 2b-e us ing triphenylphosphine (2.0 equiv) un-
der the same re ac tion con di tions and the re sults are listed in
Ta ble 1 (en tries 2-5). Whereas, , -unsaturatedynones 1f-i
underwent a smooth re duc tion even at -78 C. The strong
elec tron-withdrawing acyl substituent fa cil i tates the re duc-
tion and the ynones 1f-i are re duced at -78 C to enones 2f-i
within 2 h in 47-79% yield (en tries 6-9, Ta ble 1). Only the
trans , -un sat u rated enone is iso lated in each case. The
com pat i bil ity of a phenyl (en try 7), an ole fin (en try 8) and a
diene(entry9)moiety, whichmaynotsurviveinsodium/am-
moniaortransitionmetalcatalyzedreductionreactions,high-
lights the vir tues of this semihydrogenation re ac tion. It must
be men tioned that an elec tron-withdrawing group such as an
es ter or a keto at tached to the tri ple bond is re quired for the
semihydrogenation using triphenyphosphine and water.
Phenylacetylenederivative3isrecoveredquantitativelyafter
treat ment with triphenylphosphine in refluxing to lu ene for 12
h(entry10, Table1).
kynes,catalytichydrogenationisoneofthemostconvenient.
Thecompletereductionofalkynestothealkanesiseasilyac-
com plished with hy dro gen over cat a lytic plat i num, pal la-
dium or Raney nickel.1 How ever, most use ful from a syn-
thetic point of view is the semihydrogenation2 of al kynes to
the Z-alkenesusingLindlar’scatalyst3 or to theE-alkenes us-
ingsodiumandliquidammonia.4 Moreover,thereductionof
propargyl al co hols to the transal lyl ic al co hols can also be
performed using lithium aluminum hydride.5 The above
known meth ods have fallen al most ex clu sively into the do-
main of met als or metal hy drides and of ten en coun tered se-
verereactionconditions.Therefore,aninexpensivereagent,
which may ex hibit a sim ple re ac tion con di tion for the semi-
hydrogenation of al kynes, will at tract much at ten tion. It was
previouslyreportedthatconjugatedynonesisomerizedtothe
dienones in the pres ence of a cat a lytic amount of triphenyl-
phosphine;6 how ever, the less elec tron-deficient ynoates, re-
quired the more nucleophilic tributylphosphine6 or higher
temperatures.7 The use of triphenylphosphine for the sim ple
functionalgroupstransformationasdescribedaboveencour-
ages us to fur ther in ves ti gate this re agent. Herein, we wish to
reportanewtypeofreactionmediatedbytriphenylphosphine
that provides a convenient reduction of , -unsaturated
propargyletherstothecorrespondingallylicethers.
SchemeIoutlinesapotentialmechanismforthereduc-
tion of the 4-alkoxy ynoates and -ynones in which the role of
triphenylphosphineisproposedasanucleophile.Conjugated
ad di tion of triphenylphosphine to the tri ple bond pro duced
thezwitterionicintermediate 4. Althoughalleneintermedi-
ates were pro posed in the isomerization of tri ple bonds to the
dienes us ing triphenylphosphine,6,7 allene 5 was not iso lated.
Thismayindicatethattheprotonexchangebetweenthevinyl
carbanionandtheallylichydrogen(togive6) was not fa vor-
able. It is as sumed that the elec tron re pul sion im posed by the
RESULTSANDDISCUSSION
The , -un sat u rated ynoates and -ynones bear ing a
-alkoxy group were eas ily pre pared start ing from propargyl
alcohol(seeexperimentalsection).Reactionoftheynoate1a
and triphenylphosphine (1.1 equiv) in to lu ene at 5 C af-
forded within 6 h a mix ture ofcis and transallylicalcohols2a

870 J. Chin. Chem. Soc., Vol. 48, No. 5, 2001
Tsai et al.
Table 1. Triphenylphosphine-Mediated Reduction of Electron-Deficient Propargyl Ethers to the Allylic Ethers
Entry
1
Substrate
Product
Isolated Yield
79%
Cis/Trans ratio
2.8 : 1
EtO C C
C
2
OCO Et
2
EtO C
OCO Et
2
2
1a
EtO C C
2a
a
C
2
2
OCH Ar
OCH Ar
2
2
EtO C
2
2.0 : 1
75%
76%
1b
2b
2c
2d
a
i
3
BuO C C
C
2
i
OCH Ar
2
OCH Ar
BuO C
1.9 : 1
2
2
1c
EtO C C
C
4
5
2
OCH CO Et
2
2
OCH CO Et
EtO C
2
2
2
45%
1 : 1.2
1d
EtO C C
C
2
O(CH ) CN
2 2
EtO C
O(CH ) CN
52%
47%
79%
48%
2
1 : 3.3
2 2
1e
MeOC C
1f
2e
a
OCH Ar
2
C
6
trans only
OCH Ar
2
MeOC
2f
a
PhOC
C
C
OCH Ar
2
7
OCH Ar
trans only
trans only
2
PhOC
1g
2g
OCH Ar
O
2
a
C
C
8
OCH Ar
2
O
1h
2h
O
OCH Ar
2
C
C
a
9
OCH Ar
2
O
trans only
54%
0%
2i
1i
Ph C
C
10
OCO Et
Ph
OCO Et
2
2
3
a
Ar = 4-methoxyphenyl
ad ja cent lone pair elec trons of the ox y gen atom im peded the
formationoftheallyliccarbanion.Additionofwaterto4 gen-
eratedtheintermediate7. Re ac tion of7 with wa ter af forded
the , -un sat u rated enoate or enone 2aftereliminationof
triphenylphosphineoxide. Adeuteriumstudyfurtherproved
the pro posed re ac tion path. Thus, quench ing the re ac tion
mix ture ob tained from ad di tion of triphenylphosphine to1c
with D2O gen er ated the dideuteriated com pound 8 in 61%

Re duc tion of Propargyl Ethers to Al lyl ic Ethers
J. Chin. Chem. Soc., Vol. 48, No. 5, 2001 871
Scheme I
1. DDQ
OCH Ar
OH
2
2. H O
2
OH
H
(3)
EtO C
2
EtO C
2
(71%)
PPh
3
PPh
3
trans-2b
Ar = 4-methoxyphenyl
PPh
3
11
E
C C
X
OR
E
OR
OR
E
1
4
6
reactionconditions,trans-2b pro duced ethyl trans-4-hydroxy-
2-butenoate ( 11)10 in 71% yield (eq. 3).
H O
2
In summary, we have described a novel, practical
method for semihydrogenation of , -unsaturatedynoates
and -ynones bear ing a -alkoxygrouptothecorresponding
, -un sat u rated enoates and -enones. The fact that the semi-
hydrogenation of the car bon-carbon tri ple bonds pro ceeds
undermildreactionconditionsusingtriphenylphosphineand
wa ter of fers a new syn thetic method for this im por tant or-
ganictransformation.
OR
O
H
+
E
H
OH
2
H
H
5
H O
2
H
PPh
3
OR
not formed
Ph PO
3
E
OR
E
2
7
yield. The NMR study of 8 showedthedeuteriumincorpora-
tion(greaterthan97%)atbothvinylcarbonsandlessthan3%
ofthedeuteriumlabelingattheallyliccarbon(eq.1).
EXPERIMENTAL
1. PPh3
2. D2O
D
D
i
Allreactionswererununderanitrogenatmospherein
oven-driedglasswareunlessotherwiseindicated.Anhydrous
sol vents or re ac tion mix tures were trans ferred via an oven-
driedsyringeorcannula.Toluenewasdistilledfromcalcium
hydrideundernitrogen.Tetrahydrofuran(THF)wasdistilled
undernitrogenfromadeepbluesodiumbenzophenoneketyl
solution. Flash column chromatography, following the
method of Still,11 was car ried out with E. Merck 230-400
meshsilicagelusingtheindicatedsolvents.Analyticalthin-
layerchromatographywasperformedwithsilicagel60F254
plasticplatesof0.2-mmthickness.Theterm“concentration”
re fers to the re moval of sol vent with an as pi ra tor pump. The
term“undernitrogen”impliesthattheapparatuswasevacu-
ated (oil pump) and then filled with ni tro gen three times. Nu-
clear mag netic res o nance (NMR) spec tra were re corded at
200 and 400 MHz for 1H NMR and 50.2 and 100.4 MHz for
13CNMR,andVarianG-200(200MHz)spectrometers.Infra-
red (IR) spec tra were re corded with a JASCO IR-700 spec-
trom e ter. Mass spec tra were ac quired on a JEOL JMS-D 100
spec trom e ter at an ion iza tion po ten tial of 70 eV and are re-
ported as mass/charge (m/z) withpercentrelativeabundance.
High-resolution mass spec tra were ob tained with an AEI
MS-9 dou ble-focusing mass spec trom e ter and a JEOL JMS-
HX 110 spec trom e ter at the De part ment of Chem is try, Cen-
tralInstrumentCenter, Hsin-Chu, Taiwan. Elementalanaly-
seswereobtainedwithaPerkin-ElmerCHN-2400elemental
an a lyzer at the Microanalytical Ser vice Lab o ra tory of Na-
tionalTaiwanUniversity.
BuO2C C C
i
(1)
OCH2Ar
OCH2Ar
BuO2C
(61%)
8
1c
Ar = 4-methoxyphenyl
Based upon the re ac tion path sug gested in Scheme I,
both cis and trans 4-alkoxyenoates and -enones are formed
underthereactionconditions.However,the , -unsaturated
cis-enones readily convert to the , -unsaturated trans-
enones upon aque ous workup.2 Thus, only the trans-enones
are iso lated from re duc tion of , -unsaturatedynoneswith
triphenylphosphine(entries6-9,Table1).
The re sult ing , -unsaturatedenoatescis-2b and trans-
2bcanfurtherbemanipulatedasfollows.Treatmentofcis-2b
with DDQ (2.0 equiv) in CH2Cl2 at 30 C af forded within 4 h
ethyl cis-4-hydroxy-2-butenoate (9),8 which underwent
lactonizationuponpurificationonsilicageltoafford2(5H)-
furanone (10)9 in 68% over all yield (eq. 2). Un der the same
1. DDQ
2. H2O
OH
OCH Ar
2
EtO2C
EtO2C
cis-2b
9
Ar = 4-methoxyphenyl
silica gel separation
(68%)
(2)
O
O
10

872 J. Chin. Chem. Soc., Vol. 48, No. 5, 2001
Tsai et al.
StartingMaterials
20.32 mmol, 72%) as a col or less oil: IR (CH2Cl2) 3047, 2994,
1
Thefollowingstartingmaterialswerepreparedaccord-
ing to lit er a ture pro ce dures: ethyl 4-carbethoxy methoxy-
but-2-ynoate (1d),12 ethyl 4-(2-cyanoethoxy)but-2-ynoate
(1e)12 and 5-(4-methoxybenzyloxy)pent-3-yn-2-one (1f).13
2984, 2236, 1711, 1613, 1586, 1512, 1466, 1367 cm-1; H
NMR (200 MHz, CDCl3) 7.28 (d, J = 8.4 Hz, 2H), 6.89 (d, J
= 8.6 Hz, 2H), 4.55 (s, 2H), 4.20-4.30 (m, 4H), 3.81 (s, 3H),
1.33 (t, J = 7.2 Hz, 3H); 13C NMR (50.2 MHz, CDCl3)
159.51, 153.04, 129.74, 128.69, 113.78, 83.16, 78.02, 71.49,
61.92, 56.15, 55.03, 13.73; MS (EI) m/z (rel in ten sity) 248
(M+, 78), 201 (18), 175 (26), 147 (27), 137 (43), 136 (42), 135
(78), 121 (100), 120 (65); HRMS (EI) m/z calcd for C 14H16O4
248.1049, found 248.1051.
Ethyl 4-ethoxycarbonyloxybut-2-ynoate (1a)
A mix ture of propargyl al co hol (0.48 g, 8.50 mmol) and
n-BuLi (12.5 mL, 18.70 mmol) in 20 mL of THF was stirred
at -78 C for 0.5 h un der ni tro gen. The re ac tion mix ture was
quenched with 1.77 mL (18.70 mmol) of ethyl chloroformate
at -78 C. The re ac tion mix ture was stirred at -78 C for 30
min and 5 C for 2 h be fore be ing di luted with a mix ture of
iso-Butyl 4-(4-methoxybenzyloxy)but-2-ynoate (1c)
A mix ture of 3-(4-Methoxybenzyloxy)propyne (1.5 g,
ethylacetateandhexanes(1/5,50mL).Theresultantsolution 8.52 mmol) and n-BuLi (1.6 M in hex anes, 5.9 mL, 9.44
was washed with wa ter (100 mL 3) and brine (100 mL 3), mmol) in 20.0 mL of THF at -78 C under ni tro gen was
driedoveranhydrousmagnesiumsulfate,andconcentratedto quenched with t-butyl chloroformate (1.29 g, 9.44 mmol) to
give the crude mix ture. The crude mix ture was pu ri fied via
flashcolumnchromatography(silicagel, 5%ethylacetate/
hex anes) to give 1a (1.32 g, 6.53 mmol, 77%) as a col or less
oil: IR (CH2Cl2) 2991, 2982, 2251, 1712, 1620 cm-1; 1H NMR
(400 MHz, CDCl3) 4.85 (s, 2H), 4.27 (m, 4H), 1.33 (t, J =
7.3 Hz, 3H), 1.32 (t, J = 7.3 Hz, 3H); 13C NMR (100.4 MHz,
CDCl3) 154.1, 152.6, 80.0, 78.4, 64.7, 62.1, 54.2, 14.0,
13.8; MS (EI) m/z (rel in ten sity) 201 (M++1, 1), 155 (100),
127 (16), 111 (16), 108 (27), 101 (14), 84 (30), 67 (10);
HRMS (EI) m/z calcd for C9H13O5 (M++1) 201.0764, found
201.0762.
give 1c (2.25 g, 8.18 mmol, 96%) as a colorless oil: IR
(CH2Cl2) 3060, 2966, 2876, 2239, 1698, 1613, 1586, 1513,
1469, 1419 cm-1; 1H NMR (200 MHz, CDCl3) 7.25 (d, J =
8.6 Hz, 2H), 6.85 (d, J = 8.8 Hz, 2H), 4.51 (s, 2H), 4.21 (s,
2H), 3.95 (d,J = 6.6 Hz, 2H), 3.75 (s, 3H), 2.01-1.82 (m, 1H),
0.96 (s, 3H), 0.92 (s, 3H); 13C NMR (50.2 MHz, CDCl3)
159.37, 152.97, 129.57, 128.58, 113.61, 83.13, 76.34, 71.63,
71.36, 56.02, 54.80, 27.21, 18.56; MS (EI) m/z (relintensity)
276 (M+, 25), 219 (14), 190 (18), 175 (41), 146 (28), 137 (30),
136 (41), 135 (82), 121 (100), 120 (58). Anal. Calcd for
C16H20O4: C, 69.54; H, 7.30. Found: C, 69.50; H, 7.03.
Ethyl 4-(4-methoxybenzyloxy)but-2-ynoate (1b)
4-(4-Methoxybenzyloxy)-1-phenylbut-2-yn-1-one (1g)
Amixtureof3 -(4-Methoxybenzyloxy)propyne (1.00 g,
5.68 mmol) and n-BuLi (1.6 M in hex anes, 4.3 mL, 6.82
mmol) in 20.0 mL of THF at -78 C under ni tro gen was
quenched with benzoyl chlo ride (0.88 g, 6.25 mmol) to give
1g (1.30 g, 4.81 mmol, 82%) as a col or less oil: IR (CH2Cl2)
3060, 3008, 2988, 2959, 2912, 2866, 2228, 2060, 1723, 1582,
A mix ture of propargyl al co hol (5.0 g, 89.28 mmol) and
so dium hy dride (3.9 g, 60% in min eral oil, 97.50 mmol) in 30
mL of THF was stirred at 5 C for 0.5 h un der ni tro gen. The
re ac tion mix ture was quenched with 4-methoxybenzyl bro-
mide (17.95 g, 89.28 mmol) and stirred at 25 C for 8 h. The
re ac tion mix ture was di luted with hex ane fol lowed by the
usual workup to give the crude mix ture. The crude mix ture
waspurifiedviaflashcolumnchromatography(silicagel,5%
ethyl ac e tate/hex anes) to give 3-(4-Methoxybenzyloxy)pro-
pyne (12.60 g, 71.59 mmol, 80%). To a mix ture of 3-(4-
Methoxybenzyloxy)propyne (5.0 g, 28.41 mmol) andn-BuLi
(1.6 M in hex anes, 18.7 mL, 29.92 mmol) in 25 mL of THF at
-78 C un der ni tro gen was added ethyl chloroformate (3.24 g,
29.83 mmol). The re ac tion mix ture was stirred at -78 C for
30 min and 5 C for 2 h and was di luted with a mix ture of
ethyl ac e tate and hex anes (1/1, 100 mL). The re sul tant so lu-
tion was washed with wa ter (100 mL 3) and brine (100 mL
3), dried over an hy drous mag ne sium sul fate, and con cen-
trated to give the crude mix ture. Flash col umn chro ma tog ra-
phy (sil ica gel, 8% ethyl ac e tate/hex anes) to give 1b (5.04 g,
1
1465, 1422, 1349, 1275, 1268, 1243, 1001 cm-1; H NMR
(200 MHz, CDCl3) 8.14 (d, J = 7.0 Hz, 2H), 7.63-7.46 (m,
3H), 7.32 (d, J = 8.4 Hz, 2H), 6.91 (d,J = 8.4 Hz, 2H), 4.64 (s,
2H), 4.43 (s, 2H), 3.81 (s, 3H);13C NMR (50.2 MHz, CDCl3)
177.50, 159.69, 136.46, 134.29, 129.89, 129.63, 128.86,
128.65, 113.99, 90.29, 84.13, 71.86, 56.72, 55.18; MS (EI)
m/z (relintensity) 280 (M+, 8), 250 (3), 222 (2), 175 (2), 144
(81), 137 (48), 121 (100), 105 (59), 77 (66), 54 (18). Anal.
Calcd for C18H16O3: C, 77.12; H, 5.75. Found: C, 76.71; H,
5.57.
(E)-1-(4-Methoxybenzyloxy)hept-5-en-2-yn-4-one (1h)
Amixtureof3 -(4-Methoxybenzyloxy)propyne (1.00 g,
5.68 mmol) and n-BuLi (1.6 M in hex anes, 4.30 mL, 6.82

Re duc tion of Propargyl Ethers to Al lyl ic Ethers
J. Chin. Chem. Soc., Vol. 48, No. 5, 2001 873
mmol) in 15.0 mL of THF at -78 C un der ni tro gen was
quenched with trans-crotonyl chlo ride (0.65 g, 6.25 mmol) to
give 1h (0.95 g, 3.89 mmol, 69%) as a colorless oil: IR
(CH2Cl2) 3068, 2988, 2866, 2216, 1646, 1628, 1586, 1465,
Ethyl 4-ethoxycarbonyloxybut-2-enoate (2a)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.1 g, 8.0 mmol) to 1a (0.8 g, 4.0 mmol) at 5 C
waspurifiedviaflashcolumnchromatography(silicagel,5%
ethyl ac e tate/hex anes) to give cis-2a (0.47 g, 2.33 mmol,
58%) and trans-2a (0.17 g, 0.84 mmol, 21%) as col or less
oils.
1
1441, 1376, 1350, 1303, 1270, 1252, 1034 cm-1; H NMR
(200 MHz, CDCl3) 7.28 (d, J = 8.4 Hz, 2H), 7.24-7.09 (m,
1H), 6.89 (d, J = 8.2 Hz, 2H), 6.19 (d, J = 15.6 Hz, 1H), 4.56
(s, 2H), 4.31 (s, 2H), 3.79 (s, 3H), 1.97 (dd, J = 7.0, 1.6 Hz,
3H); 13C NMR (50.2 MHz, CDCl3) 177.81, 159.61, 150.18,
133.56, 129.80, 128.84, 113.92, 88.08, 83.46, 71.72, 56.58,
55.17, 18.30; MS (EI) m/z (relintensity) 244 (M+, 5), 213 (1),
186 (5), 171 (5), 145 (10), 137 (59), 121 (100), 108 (84), 91
(12), 77 (30), 69 (23), 66 (5). Anal. Calcd for C15H16O3: C,
73.75; H, 6.60. Found: C, 73.45; H, 6.80.
Cis-isomer
IR (CH2Cl2) 3052, 3047, 2992, 2982, 1747, 1715, 1656,
1
1390, 1373, 1342 cm-1; H NMR (200 MHz, CDCl3) 6.25
(dt, J = 11.8, 5.0 Hz, 1H), 5.83 (dt,J = 11.8, 2.4 Hz, 1H), 5.19
(dd, J = 2.2 Hz, 2H), 4.23-4.09 (m, 4H), 1.31-1.15 (m, 6H);
13C NMR (50.2 MHz, CDCl3) 165.59, 154.91, 144.12,
120.69, 65.67, 64.06, 60.33, 14.04, 13.98; MS (EI) m/z (rel
intensity)202(M+, 41), 200 (17), 199 (100), 198 (44), 183
(30), 149 (32). Anal. Calcd for C9H14O5: C, 53.46; H, 6.98.
Found: C, 53.63; H, 6.81.
(5E,7E)-1-(4-Methoxybenzyloxy)nona-5,7-dien-2-yn-4-one
(1i)
Amixtureof3 -(4-Methoxybenzyloxy)propyne (2.32 g,
13.19 mmol) and n-BuLi (1.6 M in hex anes, 9.90 mL, 15.83
mmol) in 20.0 mL of THF at -78 C un der ni tro gen was
quenched with trans-sorbic acid chloride (2.07 g, 15.83
mmol) to give 1i (2.15 g, 7.95 mmol, 61%) as a col or less oil:
IR (CH2Cl2) 3069, 3047, 2989, 2840, 2211, 1624, 1587,
Trans-isomer
IR (CH2Cl2) 3054, 2990, 2985, 1748, 1715, 1635, 1446,
1
1425, 1372, 1340, 1288 cm -1 ; H NMR (200 MHz, CDCl3)
6.93 (dt, J = 15.8, 4.6 Hz, 1H), 6.06 (dt, J = 15.8, 1.8 Hz, 1H),
4.78 (dd, J = 2.0 Hz, 2H), 4.28-4.15 (m, 4H), 1.42-1.25 (m,
6H); 13C NMR (50.2 MHz, CDCl3) 154.76, 140.50, 122.59,
65.59, 64.41, 60.58, 14.13, 14.10; MS (EI)m/z (relintensity)
202 (M+, 5), 200 (12), 189 (24), 157 (63), 129 (61), 128 (37),
127 (100), 101 (82), 100 (36), 99 (96), 86 (58), 73 (48). Anal.
Calcd for C9H14O5: C, 53.46; H, 6.98. Found: C, 53.51; H,
7.05.
1
1514, 1420, 1300, 1243, 1082 cm-1; H NMR (200 MHz,
CDCl3) 7.41 (ddd, J = 15.4, 10.0, 2.8 Hz, 1H), 7.30 (d, J =
8.8 Hz, 2H), 6.89 (d, J = 8.8 Hz, 2H), 6.30 (m, 2H), 6.14 (d, J
= 14.8 Hz, 1H), 4.58 (s, 2H), 4.34 (s, 2H), 3.80 (s, 3H), 1.90
(d, J = 5.0 Hz, 3H); 13C NMR (50.2 MHz, CDCl3) 178.00,
159.64, 149.24, 142.71, 130.09, 129.85, 129.51, 128.91,
113.95, 87.93, 83.83, 71.69, 56.67, 55.20, 18.86; MS (EI)m/z
(relintensity) 269 (M+, 1), 258 (11), 227 (5), 213 (4), 199
(12), 175 (5), 145 (18), 137 (34), 135 (42), 121 (100), 109 (9),
77 (8), 66 (3); HRMS (EI) m/z calcd for C17H18O3 270.1256,
found 270.1254.
Ethyl 4-(4-methoxybenzyloxy)but-2-enoate (2b)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.09 g, 8.00 mmol) to1b (1.00 g, 4.00 mmol) at 5
Cwaspurifiedviaflashcolumnchromatography(silicagel,
5% ethyl ac e tate/hex anes) to give cis -2b (0.50 g, 2.00 mmol,
50%) and trans-2b (0.25 g, 1.00 mmol, 25%) as col or less
oils.
General procedure for semihydrogenation of
4-alkoxyynoates and -ynones us ing triphenylphosphine
and wa ter
A mix ture of 4-alkoxyynoates or -ynones, triphenyl-
phosphine (2.0 mo lar equiv) in 20 mL of to lu ene was stirred
at 5 C (-78 C for ynones) for 2 h un der ni tro gen. The re ac-
tion mix ture was then quenched with 5 mL of wa ter at 5 C
and was di luted with a mix ture of ethyl ac e tate and hex anes
(1/5, 50 mL). The re sul tant so lu tion was washed with wa ter
(100 mL 3) and brine (100 mL 3), dried over an hy drous
mag ne sium sul fate, and con cen trated to give the crude mix-
ture.
Cis-isomer
IR (CH2Cl2) 3055, 2984, 2961, 1714, 1651, 1613, 1514,
1465, 1444, 1417, 1384 cm-1; 1H NMR (200 MHz, CDCl3)
7.26 (d, J = 8.6 Hz, 2H), 6.86 (d, J = 8.6 Hz, 2H), 6.40 (dt, J =
11.6, 4.8 Hz, 1H), 5.79 (dt,J = 11.8, 2.4 Hz, 1H), 4.61 (q, J =
2.4 Hz, 2H), 4.45 (s, 2H), 4.13 (q, J = 7.0 Hz, 2H), 3.74 (s,
3H), 1.26 (t, J = 7.0 Hz, 3H); 13C NMR (50.2 MHz, CDCl3)
165.73, 159.14, 148.19, 129.86, 129.18, 119.21, 113.58,

874 J. Chin. Chem. Soc., Vol. 48, No. 5, 2001
Tsai et al.
72.21, 67.85, 59.80, 54.12, 13.84; MS (EI) m/z (relintensity)
250 (M+, 1), 138 (39), 137 (68), 136 (100), 121 (92), 120 (57);
HRMS (EI) m/z calcd for C14H19O4 (M++1) 251.1205, found
251.1280.
(42), 35 (22), 121 (100), 120 (53); HRMS (EI) m/z calcd for
C16H22O4 278.1518, found 278.1514.
Ethyl 4-ethoxycarbonylmethoxybut-2-enoate (2d)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.46 g, 0.94 mmol) to1d (0.10 g, 0.47 mmol) at 5
Cwaspurifiedviaflashcolumnchromatography(silicagel,
5% ethyl ac e tate/hex anes) to give cis -2d (0.02 g, 0.09 mmol,
20%) and trans-2d (0.03 g, 0.12 mmol, 25%) as col or less
oils.
Trans-isomer
IR (CH2Cl2) 3049, 2987, 2961, 2939, 1715, 1663, 1613,
1
1586, 1514, 1465, 1368, 1305 cm-1; H NMR (200 MHz,
CDCl3) 7.25 (d, J = 8.2 Hz, 2H), 6.97 (dd, J = 15.6, 4.4 Hz,
1H), 6.87 (d, J = 8.2 Hz, 2H), 6.11 (dt, J = 15.6, 2.2 Hz, 1H),
4.47 (s, 2H), 4.23-4.10 (m, 4H), 3.77 (s, 3H), 1.27 (t, J = 7.0
Hz, 3H); 13C NMR (50.2 MHz, CDCl3) 166.17, 159.29,
144.73, 129.71, 129.16, 121.24, 113.73, 72.24, 68.14, 60.10,
55.00, 13.98; MS (EI) m/z (rel in ten sity) 250 (M+, 25), 221
(15), 161 (26), 137 (22), 136 (50), 121 (98), 120 (97), 98 (62),
90 (81), 89 (100). Anal. Calcd for C14H18O4: C, 67.18; H,
7.25. Found: C, 66.85; H, 6.92.
Cis-isomer
IR (CH2Cl2) 2993, 2978, 1751, 1714, 1651 cm-1; 1H
NMR (400 MHz, CDCl3) 6.42 (dt, J = 11.7, 5.6 Hz, 1H),
5.85 (d, J = 11.7 Hz, 1H), 4.69 (d, J = 5.6 Hz, 2H), 4.22 (q,J =
7.3 Hz, 2H), 4.16 (q, J = 7.3 Hz, 2H), 4.11 (s, 2H), 1.30 (t, J =
7.3 Hz, 3H), 1.27 (t, J = 7.3 Hz, 3H); 13C NMR (100.4 MHz,
CDCl3) 170.1, 165.9, 147.0, 119.9, 69.6, 60.2, 14.2; MS
(EI) m/z (rel in ten sity) 217 (M++1, 8), 170 (100), 143 (36),
129 (16), 113 (24), 101 (8), 83 (18); HRMS (EI)m/z calcd for
C10H16O5 216.1234, found 216.1000.
iso-Butyl 4-(4-methoxybenzyloxy)but-2-enoate (2c)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.85 g, 10.86 mmol) to1c (1.50 g, 5.43 mmol) at 5
Cwaspurifiedviaflashcolumnchromatography(silicagel,
5%ethylacetate/hexanes)togive cis-2c (0.76 g, 2.73 mmol,
50%) andtrans-2c (0.39g, 1.41mmol, 26%)ascolorlessoils.
Trans-isomer
1
IR (CH2Cl2) 2989, 1751, 1718, 1664 cm-1; H NMR
(400 MHz, CDCl3) 6.95 (dt,J = 15.6, 4.5 Hz, 1H), 6.10 (d,J
= 16.1 Hz, 1H), 4.27 (d, J = 4.5 Hz, 2H), 4.25 (q, J = 7.3 Hz,
2H), 4.21 (q,J = 7.3 Hz, 2H), 4.17 (s, 2H), 1.31 (t, J = 7.3 Hz,
3H), 1.27 (t, J = 7.3 Hz, 3H); 13C NMR (100.4 MHz, CDCl3)
169.9, 166.0, 142.0, 122.0, 69.9, 67.9, 61.0, 60.4, 14.2; MS
(EI) m/z (rel in ten sity) 217 (M++1, 18), 170 (100), 143 (42),
129 (10), 113 (6), 101 (6), 83 (12); HRMS (EI) m/z calcd for
C10H16O5 216.1234, found 216.0664.
Cis-isomer
IR (CH2Cl2) 3065, 3057, 2964, 1712, 1613, 1514, 1469,
1443, 1424, 1417 cm-1; 1H NMR (200 MHz, CDCl3) 7.25 (d,
J = 8.8 Hz, 2H), 6.86 (d, J = 12.1 Hz, 2H), 6.41 (dt, J = 11.8,
4.8 Hz, 1H), 5.81 (dt, J = 11.6, 2.6 Hz, 1H), 4.60 (q, J = 2.4
Hz, 2H), 4.45 (s, 2H), 3.87 (d, J = 6.6 Hz, 2H), 3.74 (s, 3H),
1.95-1.85 (m, 1H), 0.94 (s, 3H), 0.90 (s, 3H); 13C NMR (50.2
MHz, CDCl3) 165.76, 159.11, 148.13, 129.95, 129.80,
129.15, 119.15, 113.70, 113.53, 70.01, 67.87, 54.74, 27.33,
18.72; MS (EI) m/z (rel in ten sity) 278 (M+, 2), 227 (25), 217
(11), 162 (10), 137 (58), 136 (42), 121 (100), 120 (98). Anal.
Calcd for C16H22O4: C, 69.04; H, 7.97. Found: C, 69.07; H,
7.60.
Ethyl 4-(2-cyanoethoxy)but-2-enoate (2e)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (0.38 g, 1.44 mmol) to 1e (0.13 g, 0.72 mmol) at 5
Cwaspurifiedviaflashcolumnchromatography(silicagel,
5% ethyl ac e tate/hex anes) to give cis-2e (0.02 g, 0.11 mmol,
14%) andtrans-2e (0.05g, 0.28mmol, 38%)ascolorlessoils.
Trans-isomer
IR (CH2Cl2) 3052, 3048, 2965, 1715, 1613, 1514, 1468,
1424, 1304, 1286 cm-1; 1H NMR (200 MHz, CDCl3) 7.25 (d,
J = 8.8 Hz, 2H), 6.96 (dt, J = 15.8, 4.4 Hz, 1H), 6.88 (d, J =
11.8 Hz, 2H), 6.12 (dt, J = 15.8, 2.0 Hz, 1H), 4.46 (s, 2H),
4.11 (q,J = 2.0 Hz, 2H), 3.92 (d, J = 6.6 Hz, 2H), 3.76 (s, 3H),
1.97-1.87 (m, 1H), 0.95 (s, 3H), 0.91 (s, 3H); 13C NMR (50.2
MHz, CDCl3) 166.12, 159.22, 144.18, 129.60, 129.12,
121.07, 113.64. 72.21, 70.17, 68.08, 54.88, 27.46, 18.77; MS
(EI) m/z (rel in ten sity) 278 (M+, 5), 221 (21), 137 (60), 136
Cis-isomer
IR (CH2Cl2) 2989, 2879, 2254, 1712, 1651, 1631 cm-1;
1H NMR (400 MHz, CDCl3) 6.34 (dt, J = 11.7, 5.9 Hz, 1 )
5.86 (d, J = 11.7 Hz, 1H), 4.64 (d, J = 5.9 Hz, 2H), 4.16 (q,J =
7.3 Hz, 2H), 3.70 (t, J = 5.9 Hz, 2H), 2.63 (t,J = 7.3 Hz, 2H),
1.29 (t, J = 7.3 Hz, 3H); 13C NMR (100.4 MHz, CDCl3)
165.9, 146.8, 120.1, 117.6, 69.0, 65.1, 60.3, 18.8, 14.2; MS
(EI) m/z (rel in ten sity) 183 (M+, 5), 154 (8), 137 (100), 129
(20), 110 (8), 83 (48); HRMS (EI) m/z calcd for C9H13NO3

Re duc tion of Propargyl Ethers to Al lyl ic Ethers
183.2066, found 183.0891.
J. Chin. Chem. Soc., Vol. 48, No. 5, 2001 875
phosphine (0.64 g, 2.46 mmol) to 1h (0.30 g, 1.23 mmol) at
-78 Cwaspurifiedviaflashcolumnchromatography(silica
gel, 10% ethyl acetate/hexanes) to give 2h (0.15 g, 0.59
mmol, 48%) as a col or less oil: IR (CH2Cl2) 3069, 3060, 2988,
2938, 1669, 1642, 1615, 1514, 1465, 1360, 1262, 1253, 1245,
1035 cm-1; 1H NMR (200 MHz, CDCl3) 7.27 (d,J = 8.4 Hz,
2H), 7.03-6.83 (m, 4H), 6.61 (dt, J = 15.6, 1.8 Hz, 1H), 6.33
(dt, J = 15.6, 1.8 Hz, 1H), 4.50 (s, 2H), 4.17 (dd, J = 4.2, 0.8
Hz, 2H), 3.79 (s, 3H), 1.90 (dd, J= 6.8, 1.0 Hz, 3H); 13C NMR
Trans-isomer
IR (CH2Cl2) 2991, 2982, 2254, 1722, 1664, 1304 cm-1;
1H NMR (400 MHz, CDCl3) 6.94 (dt, J = 15.6, 4.3 Hz, 1 )
6.10 (d, J = 15.6 Hz, 1H), 4.21 (m, 4H), 3.71 (d, J = 8.9 Hz,
2H), 2.64 (t, J = 8.9 Hz, 2H), 1.29 (t, J = 7.3 Hz, 3H); 13
C
NMR (100.4 MHz, CDCl3) 166.0, 142.8, 122.0, 117.5, 69.8,
65.4, 60.5, 18.9, 14.2; MS (EI) m/z (rel in ten sity) 183 (M+,
100), 153 (6), 138 (100), 129 (10), 110 (22); HRMS (EI) m/z
calcd for C9H13NO3 183.2066, found 183.0890.
(50.2 MHz, CDCl3)
189.05, 159.36, 143.59, 142.56,
130.56, 129.76, 129.28, 127.42, 113.79, 72.39, 68.63, 55.09,
18.18; MS (EI) m/z (relintensity) 246 (M+, 1), 203 (5), 173
(1), 147 (2), 135 (11), 121 (100), 110 (58), 95 (26), 69 (5);
(E)-5-(4-Methoxybenzyloxy)pent-3-en-2-one (2f)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.39 g, 9.16 mmol) to 1f (1.00 g, 4.58 mmol) at
-78 Cwaspurifiedviaflashcolumnchromatography(silica
gel, 15% ethyl acetate/hexanes) to give 2f (0.47 g, 2.14
mmol, 47%)asacolorlessoil:IR(CH2Cl2) 3061, 2938, 1721,
HRMS (EI) m/z calcd for C H18O3 246.1256, found
246.1255.
15
(2E,5E,7E)-1-(4-Methoxybenzyloxy)nona-2,5,7-trien-4-one
(2i)
1
1678, 1633, 1613, 1514, 1422, 1360 cm-1; H NMR (200
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (2.52 g, 9.62 mmol) to 1i (1.30 g, 4.81 mmol) at
-78 Cwaspurifiedviaflashcolumnchromatography(silica
gel, 5% ethyl ac e tate/hex anes) to give2i (0.71 g, 2.60 mmol,
54%) as a col or less oil: IR (CH2Cl2) 3066, 3060, 3047, 2986,
2960, 2840, 1664, 1640, 1614, 1514, 1465, 1444, 1378, 1288,
1275, 1174, 1034, 1001 cm-1; 1H NMR (200 MHz, CDCl3)
7.29 (d, J = 8.4 Hz, 2H), 7.25-7.18 (m, 1H), 6.89 (d, J = 8.8
Hz, 2H), 6.90 (dt,J = 15.8, 4.2 Hz, 1H), 6.62 (dt,J = 15.8, 1.8
Hz, 1H), 6.33-6.18 (m, 3H), 4.51 (s, 2H), 4.19 (dd,J = 4.2, 2.0
Hz, 2H), 3.80 (s, 3H), 1.86 (d, J= 4.8 Hz, 3H);13C NMR (50.2
MHz, CDCl3) 189.31, 159.37, 143.93, 142.24, 140.66,
130.45, 129.79, 129.31, 127.98, 126.51, 113.82, 72.40,
68.67, 55.11, 18.63; MS (EI) m/z (relintensity) 273 (M+-1, 2),
260 (1), 176 (2), 147 (2), 136 (62), 121 (100), 108 (10), 67
(2); HRMS (EI) m/z calcd for C17H20O3 272.1412, found
272.1411.
MHz, CDCl3) 7.26 (d, J = 8.6 Hz, 2H), 6.88 (d, J = 8.8 Hz,
2H), 6.78 (dt, J = 16.0, 2.2 Hz, 1H), 6.31 (dt, J = 16.0, 1.8 Hz,
1H), 4.48 (s, 2H), 4.15 (dd, J = 1.8 Hz, 2H), 3.78 (s, 3H), 3.24
(s, 3H); 13C NMR (50.2 MHz, CDCl3) 198.01, 159.28,
143.07, 130.13, 129.56, 129.19, 113.70, 72.34, 68.26, 54.97,
26.90; MS (EI) m/z (rel in ten sity) 220 (M+, 5), 152 (9), 138
(21), 137 (93), 136 (21), 121 (100), 109 (22), 84 (24). Anal.
Calcd for C13H16O3: C, 70.89; H, 7.32. Found: C, 70.52; H,
7.29.
(E)-4-(4-Methoxybenzyloxy)-1-phenylbut-2-en-1-one (2g)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (5.20 g, 19.87 mmol) to 1g (2.79 g, 9.94 mmol) at
-78 Cwaspurifiedviaflashcolumnchromatography(silica
gel,5%ethylacetate/hexanes)togive2g (2.22 g, 7.87 mmol,
79%): IR (CH2Cl2) 3070, 3047, 3007, 2986, 2959, 1674,
1613, 1580, 1448, 1360, 1327, 1271, 1252, 1209, 1114 cm-1;
1H NMR (200 MHz, CDCl3) 7.95 (d, J = 7.0 Hz, 2H),
7.57-7.43 (m, 3H), 7.31 (d, J= 8.4 Hz, 2H), 7.11 (dt, J = 14.0,
3.8 Hz, 2H), 6.91 (d, J = 8.8 Hz, 2H), 4.56 (s, 2H), 4.26 (dd, J
= 3.8, 1.6 Hz, 2H), 3.82 (s, 3H);13C NMR (50.2 MHz, CDCl3)
190.43, 159.45, 144.62, 137.71, 132.82, 129.82, 129.38,
128.62, 128.56, 124.93, 113.90, 72.56, 68.81, 55.17; MS (EI)
m/z (relintensity) 282 (M+, 1), 276 (2), 253 (2), 223 (1), 199
(1), 174 (3), 160 (5), 146 (40), 135 (17), 121 (100), 105 (33),
91 (7), 77 (18), 51 (4); HRMS (EI) m/z calcd for C18H18O3
282.1256, found 282.1258.
iso-Butyl 4-(4-methoxybenzyloxy)-2,3-dideuterobut-2-
enoate (8)
The crude mix ture ob tained from ad di tion of triphenyl-
phosphine (0.26 g, 1.0 mmol) to 1c (0.27 g, 1.0 mmol) fol-
lowed by quench ing the re ac tion mix ture with 0.6 mL of D2O
waspurifiedviaflashcolumnchromatography(silicagel,5%
ethylacetate/hexanes)togivecis-8 (0.11 g, 0.39 mmol, 39%)
and trans-8(0.06 g, 0.21 mmol, 22%) as col or less oils.
Cis-isomer
1H NMR (200 MHz, CDCl3) 7.27 (d, J = 8.8 Hz, 2H),
6.88 (d, J = 8.6 Hz, 2H), 4.61 (s, 2H), 4.48 (s, 2H), 3.89 (d,J =
6.6 Hz, 2H), 3.80 (s, 3H), 1.94-1.83 (m, 1H), 0.93 (d, J = 6.8
(2E,5E)-1-(4-Methoxybenzyloxy)hepta-2,5-dien-4-one (2h)
The crude mix ture ob tained from ad di tion of triphenyl-

876 J. Chin. Chem. Soc., Vol. 48, No. 5, 2001
Tsai et al.
Hz, 6H); 13C NMR (50.2 MHz, CDCl3) 166.05, 159.28,
148.05, 129.95, 129.37, 113.75, 72.42, 70.25, 67.96, 55.05,
27.51, 18.91.
Key Words
Triphenylphosphine; Propargyl ether;
Semihydrogenation; , -Unsaturated ynoate;
, -Unsaturated ynone; , -Unsaturated enoate;
, -Unsaturated enone.
Trans-isomer
1H NMR (200 MHz, CDCl3) 7.28 (d, J = 8.6 Hz, 2H),
6.85 (d, J = 8.6 Hz, 2H), 4.49 (s, 2H), 4.17 (s, 2H), 3.93 (d, J =
6.6 Hz, 2H), 3.81 (s, 3H), 2.00-1.81 (m, 1H), 0.94 (d, J = 6.8
Hz, 6H); 13C NMR (50.2 MHz, CDCl3) 166.39, 159.40,
144.29, 129.78, 129.31, 121.36, 113.85, 72.42, 70.40, 68.18,
55.15, 27.65, 18.95.
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2(5H)-Furanone (10)9
A mix ture ofcis-2b (0.3 g, 1.20 mmol), DDQ (0.54 g,
2.40 mmol), and wa ter (1.0 mL) in 17.0 mL of di chloro-
methane was stirred at 25 Cfor4hundernitrogen.Thereac-
tion mix ture was di luted with di chloro methane (50.0 mL)
andfilteredthroughcelite.Theresultantsolutionwaswashed
with wa ter (100 mL 3) and brine (100 mL 3), dried over
anhydrousmagnesiumsulfate, andconcentratedtogivethe
crude mix ture. The 1H NMR spec tral data of the crude mix-
turewasidentifiedasenonoate 9.8 The crude mix ture was pu-
rifiedviaflashcolumnchromatography(silicagel,30%ethyl
acetate/hexanes)togive 10 (68.0 mg, 0.81 mmol, 68%) as a
colorlessoil:1H NMR (200 MHz, D 2O) 7.78 (dt,J = 5.4, 1.0
Hz, 1H), 6.13-6.12 (m, 1H), 4.96-4.94 (m, 2H); 13C NMR
(50.2 MHz, CDCl3) 173.90, 153.30, 121.11, 72.12.
6. Guo, C.; Lu, X. J. Chem. Soc., Perkin Trans. 1 1993,
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Ethyl (E)-4-hydroxy-2-butenoate (11)10
Thecrudemixtureobtainedfromreaction(asdescribed
above for 9) of trans-2b (0.30 g, 1.20 mmol), DDQ (0.55 g,
2.42 mmol), and wa ter (1.0 mL) was pu ri fied via flash col-
umnchromatography(silicagel,20%ethylacetate/hexanes)
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Lett. 1982, 23, 889.
1
to give 11 (0.11 g, 0.85 mmol, 71%) as a col or less oil. H
NMR (200 MHz, CDCl3) 7.03 (dt, J = 15.8, 4.0 Hz, 1H),
6.09 (dt, J = 15.4, 2.0 Hz, 1H), 4.35 (dd, J = 4.0, 2.0 Hz, 2H),
4.19 (q, J = 7.2 Hz, 2H), 1.29 (t, J = 7.2 Hz, 3H); 13C NMR
(50.2 MHz, CDCl3) 166.80, 147.37, 119.83, 61.42, 60.39,
13.95.
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ACKNOWLEDGMENTS
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The au thors grate fully ac knowl edge the Na tional Sci-
ence Coun cil of the Re pub lic of China (NSC-89-2113- M-
003-020)forfinancialsupport.
13. Mar shall, J. A.; Rob in son, E. D.; Zapata, A. J. Org.
Chem. 1989, 54, 5854.
Received March 26, 2001.