Cyclization of 5-hexenyl radicals from nitroxyl radical additions to 4-pentenylketenes and from the acyloin reaction

Article abstract of DOI:10.1139/v03-076

Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a-1d (RCH=CHCH₂X-CH ₂CH=C=O: 1a R = H, X = CH₂; 1b R = Ph, X = CH ₂; 1c R = c-Pr, X = CH₂; 1d R = H, X = O), which were observed by IR at 2121, 2120, 2119, and 2126 cm^-1, respectively, as relatively long-lived species at room temperature in hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition products 4a-4d. On thermolysis, 4a-4d underwent reversible reformation of the radicals 3, which underwent cyclization forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclopentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-(CH₂)₄CO₂H (8b) from hydrogen transfer to C_β and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative 11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin condensation, the ester CH ₂=CH(CH₂)₃CO₂Et (12a) gave the acyloin 13a (76%) as the only observed product, while PhCH=CH(CH ₂)₃CO₂CH₃ (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclopentanol (15) from cyclization of the intermediate radical anion.

Full text of DOI:10.1139/v03-076

697
Cyclization of 5-hexenyl radicals from nitroxyl
radical additions to 4-pentenylketenes and from
the acyloin reaction
Huda Henry-Riyad and Thomas T. Tidwell
Abstract: Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a–1d (RCH=CHCH2X-
CH2CH=C=O: 1a R = H, X = CH2; 1b R = Ph, X = CH2; 1c R = c-Pr, X = CH2; 1d R = H, X = O), which were ob-
served by IR at 2121, 2120, 2119, and 2126 cm–1, respectively, as relatively long-lived species at room temperature in
hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming
carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition prod-
ucts 4a–4d. On thermolysis, 4a–4d underwent reversible reformation of the radicals 3, which underwent cyclization
forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclo-
pentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-
(CH2)4CO2H (8b) from hydrogen transfer to Cβ and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring
opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative
11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin
condensation, the ester CH2=CH(CH2)3CO2Et (12a) gave the acyloin 13a (76%) as the only observed product, while
PhCH=CH(CH2)3CO2CH3 (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclo-
pentanol (15) from cyclization of the intermediate radical anion.
Key words: ketenes, free radical cyclization, TEMPO, acyloin condensation.
Résumé : On a utilisé les réarrangements photochimiques de Wolff pour produire des 4-penténylcétènes substitués en
position 5 1a–1d (RCH=CHCH2XCH2CH=C=O : 1a R = H, X = CH2 ; 1b R = Ph, X = CH2 ; 1c R = c-Pr, X = CH2 ;
1d R = H, X = O). On a observé ces produits en IR à 2121, 2120, 2119 et 2126 cm–1 respectivement, comme étant
relativement des espèces à longue durée de vie dans des solvants hydrocarbonés à la température ambiante. Ces pro-
duits substitués réagissent avec le radical nitroxyle tétraméthylpipéridinoxyle (TEMPO, TO·) en formant des radicaux
5-hexényles portant un substituant carboxy 3, qui sont piégés par un deuxième radical nitroxyle pour donner des pro-
duits de diaddition 1,2 4a–4d. Par thermolyse, ces produits 4a–4d redonnent de façon réversible le radical 3 qui par
cyclisation forme les dérivés de l’acide cyclopentanecarboxylique 6 ou 11 comme produits majoritaires. Toutefois dans
le cas du composé 1b le dérivé cyclopentane se forme de façon réversible, et en prolongeant les temps de réaction le
seul produit obtenu est le : PhCH=CH(CH2)4CO2H (8b) résultant du transfert d’hydrogène sur Cβ et du clivage du
groupe TEMPO. L’ouverture du cycle du radical cyclopropylcarbinyle dans le radical cyclisé 5c obtenu à partir du
composé 1c conduit au dérivé 2-(4-N-tétraméthylpipéridinyloxybut-1-ényl)cyclopentane 11 comme produit majoritaire.
Dans un essai de cyclisation du radical 5-hexényle de l’anion radicalaire intermédiaire de la condensation acyloïne,
l’ester CH2=CH(CH2)3CO2Et (12a) donne l’acyloïne 13a (76%) comme seul produit observé, tandis que le composé
PhCH=CH(CH2)3CO2CH3 (12b) avec le Na dans le toluène donne 21% de l’ acyloïne 13b et 42% de 2-
benzylcyclopentanol (15) à partir de la cyclisation de l’anion radicalaire intermédiaire.
Mots clés : cétènes, radical libre, cyclisation, TEMPO, condensation acyloïne.
[Traduit par la Rédaction] Henry-Riyad and Tidwell 704
Introduction
diazo ketones 2 (eq. [1]) these reactions were found to pro-
ceed by radical attack at the carbonyl carbon forming enolic
radicals 3 which then were trapped by a second TEMPO
giving the 1,2-diaddition products 4 (eqs. [2] and [3]). Cycli-
zation of the intermediate 5-hexenyl radicals 3 forming cyclo-
pentylmethyl radicals 5 and capture as cyclopentanes 6 was
As part of our studies of the reactions of ketenes with
aminoxyl radicals (1), we have examined the reactivity of 4-
pentenylketenes 1a, 1b with TEMPO (TO·) (1a). For 1a
(R = H, X = CH2) and 1b (R = Ph, X = CH2) generated from
Received 8 January 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 18 June 2003.
This paper is dedicated to Professor Don Arnold in recognition of his many achievements in chemistry.
H. Henry-Riyad and T.T. Tidwell.1 Department of Chemistry, University of Toronto, Toronto, ON M5S 3H6, Canada.
1Corresponding author (e-mail: ttidwell@chem.utoronto.ca).
Can. J. Chem. 81: 697–704 (2003)
doi: 10.1139/V03-076
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Can. J. Chem. Vol. 81, 2003
evidently too slow to compete with capture of 3 by TEMPO
at these concentrations. However, on thermolysis of 4a in
tert-butyl alcohol according to the protocol of Studer (2a)
cyclization forming 6a was successful, indicating that upon
equilibration of 3a and 4a cyclization to 5a was followed by
capture by TEMPO forming 6a as a cis–trans mixture
(eq. [3]).
gave no detectable cyclized product, but instead the
carboxylic acid 8b was isolated (54%), along with TH
(14%). Experiments at shorter time intervals revealed that
8b was not the first formed product, but the cyclized ester
6b (mixture of stereoisomers) was present early in the reac-
tion, as well as the cyclized acid 7b (eq. [6]).
As a test of the source of carboxylic acids and TH in these
reactions, the thermolysis of the ester 9 of phenylacetic acid
and 2,2,6,6-tetramethylpiperidinol under Studer’s conditions
was examined. This reaction was found to give phenylacetic
acid (35%) and TH (30%) after 7 days at 130°C (eq. [7]).
The cyclopropyl group serves as a useful clock for investi-
However, when the 1, 2-bis(TEMPO) addition product 4b
from 5-phenyl-4-pentenylketene (1b) was heated as in
eq. [4], the corresponding cyclization product 6b was not
observed, and other reactions appeared to be taking place
(1a). Further investigations have now been carried out to
elucidate the behavior of 4b, and the reactivity of 5-
cyclopropyl-4-pentenylketene 1c as well as the 2-oxa-4-
pentenylketene analogue 1d have been studied, and the re-
sults are reported here.
The reactions of ketenes with TEMPO and the reactions
of these substrates are of interest because of current studies
of the reactions of TEMPO with free radicals and the chem-
istry of the adducts (2, 3), especially in living free radical
polymerization (4). Free radical rearrangements are also of
wide applicability in organic synthesis (5, 6). In other recent
studies designed to examine the formation and reaction of
TEMPO esters, we have reported the thermal reactivity of
Ph3CCO2T (1j) and the addition of TEMPO to the unreactive
ketenes CH2=C=O and PhMe2SiCH=C=O (1k).
gating the presence of free radicals and so the new 5-
cyclopropyl-substituted 4-pentenyl diazomethyl ketone 2c
was prepared as shown (eqs. [8] and [9]). Photolysis of 2c
gave the ketene 1c as identified by the IR absorption at
2119 cm–1 (eq. [10]), and addition of TEMPO to the pre-
formed ketene gave the 1,2-diaddition product 4c in 71%
yield (eq. [11]). Thermolysis of 4c resulted in the formation
of the cyclized ester 11 (mixture of stereoisomers) in 65%
yield, along with TH in 15% yield (eq. [11]).
Results
The thermolysis reaction of the bis(TEMPO) adduct 4a
(1a) from 1a in tert-butyl alcohol by the protocol of Studer
(2a) was reexamined, and, in addition to the cyclized
TEMPO ester 6a (70%), tetramethylpiperidine (TH, 8%)
was also identified (eq. [5]). The presence of carboxylic acid
absorption in the IR was also detected in the crude product,
but the acid was not isolated.
Heating the bis(TEMPO) adduct 4b (1a) of 5-phenyl-4-
pentenylketene 1b at 130°C for 18 h in tert-butyl alcohol
© 2003 NRC Canada

Henry-Riyad and Tidwell
699
The incorporation of hetero atoms in 5-hexenyl radical
chains is a method to enhance their propensity for cycli-
zation to cyclopentylmethyl radicals (4), and so the ketene
precursor 2-oxa-4-pentenyl diazomethyl ketone 2d was pre-
pared from 3-oxa-5-hexenoic acid (7h) by conversion to the
acyl chloride and reaction with diazomethane. Photolysis of
2d in pentane at room temperature gave the ketene 1d, as
identified by its ketenyl IR absorption at 2126 cm–1
(eq. [12]), and upon reaction with TEMPO this gave the
product 4d of 1,2-addition of two molecules of TEMPO to
the ketenyl moiety (eq. [13]). Thermolysis of 4d in tert-
butanol at 130°C gave the cyclized product 6d (cis–trans
mixture) in 67% yield (eq. [13]).
Discussion
As already reported (1a), the formation of the cyclized
product 6a (eq. [4]) is in accord with the mechanism in
which the initially formed product 4a of 1,2-diaddition of
TEMPO reforms the radical 3a upon heating, and this under-
goes cyclization leading to 6a, which is stable to ring open-
ing. The formation of carboxylic acids and TH as observed
from 4a–4c and from PhCH2CO2T (9) under these condi-
tions is however unusual, and this reaction is under further
investigation.
2-Oxa-4-pentenylketene (1d) reacted similarly to 1a with
TEMPO (eq. [12]), and formed the cyclized product 6d upon
thermolysis in an analogous manner (eq. [13]). However, no
improved efficiency of cyclization was observed compared
to the carbon analogue 1a.
The initial 1,2-diaddition of TEMPO to 5-phenyl-
pentenylketene 1b (eqs. [2] and [3]) was also reported previ-
ously (1a). Upon heating this is also found to form the
cyclized product 6b at short reaction time, analogously to
the previously observed formation of 6a (eq. [4]). However,
6b is reactive under these conditions, and is gradually con-
verted to 8b, evidently by reforming the intermediate radical
5b which reopens to 3b, which abstracts hydrogen and also
undergoes loss of the TEMPO group as found for
PhCH2CO2T (eqs. [16] and [17]).
The acyloin condensation (8) is a reaction proposed to in-
volve radical anion intermediates formed by electron transfer
from sodium to esters, but we are unaware of examples of
radical cyclization under these conditions. As a further test
of the cyclization of 5-hexenyl radicals, the acyloin conden-
sations of ethyl 5-hexenoate (12a) (7j) and methyl 6-phenyl-
5-hexenoate (12b) (7b, 7i) were investigated. Reaction of
12a with sodium in toluene gave the acyloin 13a in 76%
yield as the only isolated product (eq. [14]), and for further
characterization this was oxidized to the diketone 14a
(45%). Similar reaction of 12b gave the cyclized product
cis-2-benzylcyclopentane 15 (42%) along with the acyloin
13b (21%) (eq. [15]). Oxidation of 13b formed the corre-
sponding α-diketone 14b (52%). The stereochemistry of 15
was assigned by comparison with the reported spectra (7j).
The formation of 11 (eq. [11]) in the reaction of TEMPO
with 5-cyclopropyl-4-pentenylketene (1c) indicates that radi-
cal 3c is formed by TEMPO dissociation from 4c, and then
undergoes cyclization to 5c (eq. [18]). Ring opening of 5c
gives 16 which is captured by TEMPO forming 11
(eq. [19]).
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Can. J. Chem. Vol. 81, 2003
1 to 2 mL THF cooled in an ice water bath, of a hexane solu-
tion of n-butyllithium (1.0 equiv) via syringe, followed by
stirring the mixture at room temperature for 15–30 min prior
to use (7d).
(4-Carboxybutyl)triphenylphosphonium bromide (7c, 7f, 7g)
was prepared by addition of Ph3P (5.06 g, 19.3 mmol) to a
solution of 5-bromovaleric acid (3 g, 16.6 mmol) in aceto-
nitrile (7.5 mL). The resulting mixture was stirred at 80°C
under reflux for 24 h, concentrated, and the residue was
washed with benzene, hexane, and ether and dried giving (4-
carboxybutyl)triphenylphosphonium bromide (6.75 g, 92%)
as a white solid. H NMR (400 MHz, CDCl3) δ: 1.70 (m, 2,
CH2CH2CH2), 1.91 (m, 2, CHCH2CH2), 2.90 (t, 2, CH2CO,
J = 6.9 Hz), 3.68 (m, 1, Ph3PCH), 7.73–7.78 (m, 15, Ar).
The possibility of 5-hexenyl radical cyclization during the
acyloin condensation does not appear to have been previ-
ously examined, but acyloin reactions of linoleic and oleic
esters gave the normal acyloin products, and did not undergo
the potential radical cyclization which would form 10-
membered rings (8a). In this study, ethyl 5-hexenoate (12a),
which could form a five-membered ring by radical cycli-
zation, gave the normal acyloin product (eq. [14]). However,
when the double bond is activated with a phenyl substituent
cyclization does occur with the formation of 15 from 12b
(eq. [15]). Evidently the intermediate radical anion 17 from
single electron transfer to 12b (eq. [20]) undergoes competi-
tive acyloin condensation, forming 13b, and cyclization
leading to 15 via 18 (eq. [21]). Related radical cyclizations
of radical anions from ketones are known (5b). The scope
and mechanism of this interesting reaction are under further
study.
1
Thermolysis of 4a
The bis-TEMPO adduct 4a (20 mg, 0.047 mmol) in de-
gassed t-BuOH (4 mL) was heated 24 h in a sealed ampoule
at 130°C, and GC analysis indicated the presence of 2,2,6,6-
tetramethylpiperidine (8 ± 1%). The solvent was removed
under reduced pressure and chromatography (CHCl3–
MeOH, 9:1) gave a product containing carboxylic acid based
on the IR spectrum (CDCl3) 3516, 1745, 1700 cm–1. Base
extraction and rechromatography (CHCl3–MeOH, 9:1) af-
forded 6a (14 mg, 70%, E:Z (45:55)) (1a). The carboxylic
acid product was not recovered from the aqueous layer.
Thermolysis of N-2,2,6,6-tetramethylpiperidinyl 2-(N-
2,2,6,6-tetramethyl piperidinyloxy)-7-phenyl-5-
heptenoate (4b)
The bis-TEMPO adduct 4b (20 mg, 0.040 mmol) under
nitrogen in degassed t-BuOH (4 mL) was sealed in an am-
poule and heated 18 h at 132–135°C in a refluxing xylene
bath. Gas chromatography showed the presence of TH (14 ±
2%). The solvent was removed under reduced pressure and
chromatography (CHCl3–MeOH, 9:1) gave the known (7b)
uncyclized acid 8b PhCH=CH(CH2)4CO2H (54%). IR
In summary, radical cyclization of the 5-hexenyl radicals
3 resulting from TEMPO addition to 4-pentenylketenes 1
does not compete with the addition of a second TEMPO
forming the 1,2-diaddition products 4. However, upon heat-
ing under the conditions of Studer (2a) the products 4 re-
versibly reform 3, which cyclize to cyclopentylmethyl
radicals 5 which are captured by TEMPO for 1a and 1d, and
for 1b are in equilibrium with 3b, which eventually reacts by
hydrogen abstraction. The cyclopropyl derivative 5c under-
goes cyclopropylcarbinyl radical ring opening forming 11
after addition of TEMPO. Degradation of TEMPO esters to
carboxylic acids and TH is noted, and is under further study.
5-Hexenyl radical cyclization is observed in the radical ion
intermediate of the acyloin condensation when the double
bond is activated with a phenyl substituent.
1
(CDCl3) (cm–1): 1703, 3518. H NMR (400 MHz, CDCl3) δ:
1.54–1.83 (m, 4, CH2CH2CO2H), 2.23 (m, 2, CHCH2CH2),
2.42 (m, 2, CH2CH2CO2H), 5.66 (m, 1, cis-PhCH=CH), 6.18
(m, 1, trans-PhCH=CH), 6.37 (m, 1, PhCH=CH),), 7.33 (m,
5, Ar). 13C NMR (100 MHz, CDCl3) δ: 24.5, 28.9, 32.8,
33.9, 126.2, 127.1, 128.7, 128.8, 128.9, 129.6, 130.4, 130.5,
131.3, 132.5, 137.6, 137.9, 178.8 (CO). EI-MS (m/z): 204
(M+), 186, 157, 144, 130, 117, 104, 91, 77, 65. HR-EI-MS
(m/z) calcd. for C13H16O2: 204.1143; found: 204.1150.
Heating of 4b with shorter reaction times gave N-2,2,6,6-
tetramethyl-piperidinyl 2-(phenyl-N-2,2,6,6-tetramethylpiperi-
dinyloxymethyl)cyclo pentanecarboxylate (6b) which was
1
purified by chromatography (CH2Cl2). H NMR (500 MHz,
Experimental
CDCl3) δ: 2.66–2.85 (m, 44), 3.25–3.28 (m, 1, CHCO2T),
4.76 (d, 1, CHPhOT, J = 6.8 Hz), 7.22–7.39 (m, 5, Ar). 13C
NMR (125 MHz, CDCl3) δ: 17.2, 17.3, 20.5, 20.6, 23.4,
24.8, 28.7, 29.1, 29.7, 31.1, 31.9, 32.1, 32.2, 32.3, 32.7,
39.0, 39.1, 39.2, 39.25, 45.7, 47.3, 59.8, 60.1, 87.7
CH(OT)Ph, 126.0, 127.2, 127.5, 128.5, 128.9, 131.0, 137.7,
140.9, 175.5 (CO). EI-MS (m/z): 499 (M+), 326, 187, 157,
140, 117, 91, 69, 55. HR-EI-MS (m/z) calcd. for
C31H51N2O3: 499.3907; found: 499.3900. IR (CDCl3) (cm–1):
1751. Further chromatography (EtOAc–MeOH, 3:7) gave 2-
(phenyl-N-2,2,6,6-tetramethylpiperidinyloxymethyl)cyclo-
Chromatography was carried out on silica gel. Solutions
for reactions of TEMPO products were degassed and kept
under argon or nitrogen. Gas chromatography (GC) was car-
ried out with a flame ionization detector and a Simplicity 5
column (poly-5% diphenylsiloxane – 95% dimethylsiloxane).
The disubstituted alkenes studied were cis–trans isomers
that were not separated but the NMR spectra were assigned
from the mixtures.
Lithium hexamethyldisilazide was prepared, by addition to
a solution of 1,1,1,3,3,3-hexamethyldisilazane (1.04 equiv) in
© 2003 NRC Canada

Henry-Riyad and Tidwell
701
pentane carboxylic acid (7b). IR (CDCl3) (cm–1): 3513,
1701. H NMR (500 MHz, CDCl3) δ: 1.06–2.38 (m, 24),
mer), 1.48–1.53 (m, 1, Z-isomer), 1.73 (distorted q, 2,
CH2CH2CH2), 2.00–2.35 (m, 4), 4.80 (dd, 1, J = 10.6,
6.3 Hz, c-PrHCH=CH, Z-isomer), 4.98 (dd, 1, J = 12.3,
8.2 Hz, c-PrHCH=CH, E-isomer), 5.23 (s, 1, COCHN2),
5.28 (dt, 1, J = 10.4, 9.9 Hz, CH=CHCH2, Z-isomer), 5.45
(dt, 1, J = 13.2, 6.4 Hz, CH=CHCH2, E-isomer). 13C NMR
(100 MHz, CDCl3) δ: 7.2, 10.0, 13.9, 25.4, 27.2, 32.2, 126.9
(CH=CHCH2), 135.3 (c-PrCH=CH), 195.2 (CO). EI-MS
m/z: 179 (MH+), 149 (M+ – N2), 135, 121, 107, 91. HR-EI-
MS m/z calcd. for C10H14N2O: 179.1186; found: 179.1184.
1
2.78–2.80 (m, 1, CHCHOTPh), 2.98–3.02 (m, 1, CHCO2H),
4.80 (d, 1, CHOTPh) J = 8.9 Hz), 7.23–7.36 (m, 5, Ar). 13C
NMR (125 MHz, CDCl3) δ: 17.4, 21.5, 22.9, 25.4, 30.3,
31.8, 38.5, 40.0, 46.9, 47.7, 53.7, 61.2, 88.8 (CHOTPh),
126.5, 127.6, 128.0, 128.6, 129.1, 130.1, 130.4, 139.7, 178.9
(CO). EI-MS (m/z): 360 (M+), 293, 239, 203, 185, 157, 142,
125, 91, 69, 55. HR-EI-MS (m/z) calcd. for C22H34NO3:
360.2534; found: 360.2539.
6-Cyclopropyl-5-hexenoic acid (10)
5-Cyclopropyl-4-pentenylketene (1c) and reaction with
TEMPO
4-Carboxy-n-butyltriphenylphosphonium bromide (5 g,
11.3 mmol) in THF (15 mL) was treated with lithium
hexamethyldisilazide (23.7 mmol) in THF (4 mL) at 25°C
with stirring. After 15 min, cyclopropanecarboxaldehyde
(0.79 g, 11.3 mmol) in THF (5 mL) was added at 25°C, rap-
idly decolorizing the red-orange mixture. After 15 min, wa-
ter (25 mL) and ether (25 mL) were added. The organic
phase was rinsed with 20 mL of water. The combined aque-
ous solution was washed with EtOAc (25 mL), acidified
with 10% HCl, and extracted with EtOAc. The united
EtOAc extracts were rinsed with H2O, dried with Na2SO4,
and concentrated. Kugelrohr distillation gave 10 (1.12 g,
1-Diazo-7-cyclopropyl-6-hepten-2-one (2c, 100 mg,
0.56 mmol) in pentane (75 mL) was photolyzed for 30 min
with 250-nm light to give ketene 1c (IR: 2119 cm–1).
TEMPO (183 mg, 1.18 mmol, 2.1 equiv) was added to the
preformed ketene and the solution was left stirring at room
temperature for 24 h. Chromatography with CH2Cl2 gave 4c
(191 mg, 0.40 mmol, 71%) E/Z isomers (50:50). IR (CDCl3)
1
(cm–1): 1770. H NMR (400 MHz, CDCl3) δ: 0.28–0.31 (m,
2), 0.62–0.65 (m, 2, E-isomer), 0.68–0.72 (m, 2, Z-isomer),
1.08–2.20 (m, 43), 4.48 (distorted t, 1, CH2CHOT), 4.75 (dd,
1, J = 10.2, 7.3 Hz, c-PrHCH=CH, Z-isomer), 4.92 (dd, 1,
J = 9.4, 8.2 Hz, CH=CHCH2, E-isomer), 5.31 (dt, 1, c-
PrHCH=CH, Z-isomer), 5.45 (dt, 1, J = 13.9, 7.5 Hz,
CH=CHCH2, E-isomer). 13C NMR (100 MHz, CDCl3) δ:
6.6, 7.1, 9.8, 13.7, 17.2, 17.4, 20.8, 20.9, 24.7, 24.9, 27.8,
32.1, 32.3, 32.4, 32.6, 34.8, 39.5, 40.7, 60.2, 60.5, 83.7
(CHOT), 127.6, 127.7 (CH=CHCH2), 134.6, 134.7 (c-
PrCH=CH), 171.9 (CO2T). EI-MS m/z: 464 (MH+), 448
(M+ – CH3), 322 (M+ – T), 306, 278, 182, 156 (TO+), 140
(T+), 126, 83, 55. HR-EI-MS m/z calcd. for MH+
C28H51N2O3: 463.3869; found: 463.3899.
1
64%) (E/Z isomers, 1:1). H NMR (400 MHz, CDCl3) δ:
0.30–0.32 (m, 2), 0.63–0.67 (m, 2, E-isomer), 0.69–0.73 (m,
2, Z-isomer), 1.49–1.58 (m, 1), 1.65–2.41 (m, 6), 4.80 (dd,
1, J = 10.6, 9.8 Hz, c-PrHCH=CH, Z-isomer), 5.02 (dd, 1,
J = 15.2, 8.2 Hz, c-PrHCH=CH, E-isomer), 5.30 (dt, 1, J =
10.6, 6.2 Hz, CH=CHCH2, Z-isomer), 5.45 (dt, 1, J = 15.2,
6.4 Hz, CH=CHCH2, E-isomer).
6-Cyclopropyl-5-hexenoyl chloride
Oxalyl chloride (1.05 g, 8 mmol) was added dropwise to a
stirred solution of 6-cyclopropyl-5-hexenoic acid (10, 0.76 g,
4 mmol) in CCl4 (10 mL) and stirred for 2 h. The solvent
was removed in vaccuo to give 6-cyclopropyl-5-hexenoyl
chloride as a dark brown oil (1.20 g, 92%) containing E/Z
Thermolysis of 4c
The bis-TEMPO adduct 4c (50 mg, 0.108 mmol) in de-
gassed t-BuOH (5 mL) was heated in a sealed ampoule at
130°C for 18 h. GC analysis indicated the presence of
2,2,6,6-tetramethylpiperidine (15 ± 2%). Concentration and
chromatography (CHCl3–MeOH, 9:1) afforded the cyclized
ester 11 containing carboxylic acid. IR (CDCl3) (cm–1):
3512, 1740, 1702. Base extraction and chromatography
(CH2Cl2–MeOH, 9:1) afforded ester 11 (32 mg,
0.069 mmol, 65%). IR (CDCl3) (cm–1): 1750. 1H NMR
(500 MHz, CDCl3) δ: 1.08–2.00 (m, 42), 2.22 (dt, 2,
CH2CH2OT), 2.51 (m, 1, Z-CHCO2T), 2.79 (m, 1, E-
CHCO2T), 3.71–3.74 (t, 2, J= 6.71 Hz, CH2OT), 5.43–5.48
(m, 1, c-PnCH=CH), 5.52–5.56 (m, 1, c-PnCH=CH). 13C
NMR (125 MHz, CDCl3) δ: 17.4, 20.4, 20.8, 24.2, 24.8,
25.0. 30.0, 30.4, 31.5, 32.2, 33.3, 33.6, 39.8, 47.7, 50.4,
56.0, 76.5 (CH2OT), 127.5 (CH=CHCH2), 133.9 (c-
PnCH=CH), 180.6 (CO2T). EI-MS m/z: 463 (MH+), 447
(M+ – CH3), 306 (M+ – OT), 278 (M+ – CO2T), 182, 156
(TO), 140 (T), 126, 109, 93, 83, 69, 55. HR-EI-MS m/z
calcd. for C28H50N2O3: 462.3816; found: 462.3821.
1
(50:50), used subsequently without further purification. H
NMR (400 MHz, CDCl3) δ: 0.31–0.32 (m, 2), 0.71–0.73 (m,
2, E-isomer), 0.74–0.79 (m, 2, Z-isomer), 1.52–1.6 (m, 1),
1.90 (distorted q, 2, CH2CH2CH2), 2.32 (dt, 2, CHCH2CH2),
3.05 (t, 2, J = 7.2 Hz, CH2COCl), 4.84 (dd, 1, J = 10.5,
8.4 Hz, c-PrHCH, Z-isomer), 5.20 (dd, 1, J = 13.2, 7.7 Hz,
c-PrHCH=CH, E-isomer), 5.35 (dt, 1, J = 9.4, 7.5 Hz,
CH=CHCH2, Z-isomer), 5.50 (dt, 1, J = 11.4, 8.5 Hz,
CH=CHCH2, E-isomer).
1-Diazo-7-cyclopropyl-6-hepten-2-one (2c)
6-Cyclopropyl-5-hexenoyl chloride (1.20 g, 7.0 mmol) in
ether (5 mL) was added dropwise over a period of 0.5 h to a
stirring cooled solution of 0.018 mol of diazomethane (3
equiv) in ether (60 mL) which the solution was stirred at
0°C for 2 h. Excess diazomethane was removed by evacuat-
ing with a water aspirator through an empty Erlenmeyer
flask and quenched in acetic acid, and the solution was con-
centrated. Chromatography (EtOAc–hexane, 3:7) gave 2c
(0.92 g, 5.2 mmol, 74%) as a yellow oil containing E/Z iso-
Allyloxyacetyl chloride
mers (47:53). IR (pentane) (cm–1): 2102, 1662. H NMR
(400 MHz, CDCl3) δ: 0.29–0.32 (m, 2), 0.63–0.66 (m, 2, E-
isomer), 0.69–0.74 (m, 2, Z-isomer), 1.32–1.34 (m, 1, E-iso-
Oxalyl chloride (3.99 g, 2.7 mL, 0.03 mol) was added
dropwise to a stirred solution of allyloxyacetic acid (7 h,
1.75 g, 0.015 mol) in dichloromethane (20 mL) followed by
1
© 2003 NRC Canada

702
Can. J. Chem. Vol. 81, 2003
stirring at room temperature for 2 h. The solvent was re-
moved in vacuo to give allyloxyacetyl chloride as a yellow
oil (1.85 g, 0.0137 mol, 92%) used subsequently without
further purification. H NMR (400 MHz, CDCl3) δ: 4.12–
4.23 (m, 4, CH2OCH2COCl), 5.26–5.39 (m, 2, CH2=CH),
5.85–5.98 (m, 1, CH2=CH).
ter 15 min, water and ether were added, the organic phase
was rinsed with water (20 mL) and the combined aqueous
solution was washed with EtOAc (25 mL), acidified with
10% HCl, and extracted with EtOAc. The united EtOAc ex-
tracts were rinsed with H2O, dried with Na2SO4, and con-
centrated. Kugelrohr distillation gave 6-phenyl-5-hexenoic
1
1
acid (0.68 g, 80%) containing trans/cis isomers (87:13). H
NMR (400 MHz, CDCl3) trans-isomer δ: 1.70–2.56 (m, 6),
6.15 (m, 1, PhCH=CH), 6.45 (m, 1, PhCH=CH), 7.20 (m, 5,
Ar), 10.65 (br s, 1, CO2H); cis-isomer δ: 1.70–2.56 (m, 6),
5.60 (m, 1, PhCH=CH), 6.45 (m, 1, PhCH=CH), 7.20 (m, 5,
Ar), 10.65 (br s, 1, CO2H).
1-Diazo-4-oxa-6-hexen-2-one (2d)
Allyloxyacetyl chloride (1 g, 7 mmol) was dissolved in
ether (5 mL) and added dropwise over 0.5 h to a stirring
cooled solution of of diazomethane (0.018 mol, 2.5 equiv) in
ether (100 mL), and the solution was stirred cold for 2 h.
The excess diazomethane was removed by evacuating with a
water aspirator pump and quenched into acetic acid. Con-
centration and chromatography (EtOAc–hexane, 1:3) gave
2d (0.71 g, 5.1 mmol, 69%) as a yellow oil. IR (pentane)
6-Phenyl-5-hexenoyl chloride (7b)
Oxalyl chloride (1.05 g, 8 mmol) was added dropwise to a
stirred solution of 6-phenyl-5-hexenoic acid (0.76 g,
4.0 mmol) in CCl4 (10 mL) followed by stirring at room
temperature for 2 h. The solvent was removed in vaccuo to
give 6-phenyl-5-hexenoyl chloride as a yellow oil (0.81 g,
3.9 mmol, 97%) containing E/Z isomers (85:15), used subse-
1
(cm–1): 2107, 1661. H NMR (400 MHz, CDCl3) δ: 3.95–
4.04 (m, 4, CH2OCH2COCHN2). 5.17–5.37 (m, 2,
CH2=CH), 5.73 (s, 1, COCHN2), 5.79–5.92 (m, 1,
CH2=CH). 13C NMR (100 MHz, CDCl3) δ: 53.3, 57.3, 67.2,
76.4, 118.1 (CH=CHCH2), 133.7 (CH=CH), 193.9 (CO). EI-
MS m/z: 141 (MH+), 84, 69, 55. HR-EI-MS m/z calcd. for
MH+ C6H9N2O2: 141.0657; found: 141.0664.
1
quently without further purification. H NMR (400 MHz,
CDCl3) δ: 1.89 (distorted q, 2, CH2CH2CH2), 2.29 (dt, 2,
CHCH2CH2), 2.95 (t, 2, J = 6.8 Hz, CH2COCl), 6.16 (m, 1,
PhCH=CH, Z-isomer), 5.61 (m, 1, PhCH=CH, E-isomer),
6.41 (m, 1, PhCH=CH, E and Z isomers), 7.31–7.36 (m, 5H,
Ar).
(2-Oxa-4-pentenyl)ketene (1d) and reaction with
TEMPO
1-Diazo-3-allyloxy-2-propanone (2d, 250 mg, 1.8 mmol)
in 75 mL of pentane was photolyzed for 60 min with 250-
nm light to give the corresponding ketene (IR: 2126 cm–1).
TEMPO (585 mg, 3.8 mmol, 2.1 equiv) was added to the
preformed ketene and the solution was stirred at room tem-
Methyl 6-phenylhex-5-enoate (12b) (7i)
To a stirred mixture of methanol (0.2 mL, 4.9 mmol) and
triethylamine (0.62 mL, 4.9 mmol) in CH2Cl2 (30 mL) at
0°C was added of 6-phenyl-5-hexenoyl chloride (1 g,
4.9 mmol). The reaction mixture was stirred for 20 min then
2 M HCl (10 mL) was added. The organic layer was washed
with NaHCO3 and brine, dried, and concentrated. Chroma-
tography (CH2Cl2) yielded 12b, (0.90 g, 4.4 mmol, 90%) as
a yellow oil (E/Z isomers, 93:7). 1H NMR (400 MHz,
perature for
6 h. Concentration and chromatography
(CH2Cl2) gave the bis-adduct 4d (562 mg, 1.32 mmol, 73%).
1
IR (CDCl3) (cm–1): 1773. H NMR (400 MHz, CDCl3) δ:
1.22–1.82 (m, 36), 3.94–4.05 (m, 2, OCH2CHOT), 4.11 (d,
2, J = 4.2 Hz, CH2=CHCH2O), 4.68 (t, 1, J = 5.5 Hz,
CHOT), 5.15–5.31 (m, 2, CH2=CH), 5.83–5.94 (m, 1,
CH2=CH). 13C NMR (100 MHz, CDCl3) δ: 17.4, 17.5, 20.6,
20.8, 21.0, 21.1, 32.4, 34.0, 34.4, 39.6, 39.7, 40.8, 60.5,
60.7, 70.1, 72.8, 83.6 (CHOT), 117.7 (CH2=CH), 135.0
(CH2=CH), 170.5 (CO2T). EI-MS m/z: 410 (MH+ – CH3),
308, 285 (M+ – T), 268 (M+ – TO), 240 (M+ – CO2T), 156
(TO+), 140 (T), 126, 83, 69, 58. ES-MS m/z 425 (MH+), 447
(MNa+), 463 (MK+).
The bis-TEMPO adduct 4d (100 mg, 0.23 mmol) in de-
gassed t-BuOH (5 mL) was heated for 5 h at 135°C in a
refluxing xylene bath. After concentration chromatography
(CHCl3–MeOH, 9:1) gave the cyclized product 6d (67 mg,
0.16 mmol, 67%). IR (CDCl3) (cm–1): 1756. 1H NMR
(500 MHz, CDCl3) δ: 1.04–1.70 (m, 36), 2.74–2.97 (m, 2),
3.72–4.10 (m, 6, CH2). 13C NMR (125 MHz, CDCl3) δ: 17.3,
17.5, 20.2, 20.3, 20.4, 20.9, 23.0, 30.0, 32.2, 32.4, 32.5,
33.4, 33.5, 39.3, 39.4, 39.9, 41.5, 43.2, 46.1, 59.9, 60.2,
60.3, 74.9 (CH2OT), 172.9 (CO2T). EI-MS m/z: 341, 311,
270, 216, 156, 142, 126, 83, 69. ES-MS m/z: 447 (MNa+),
463 (MK+).
CDCl ) trans-12b : 1.82–1.88 (q, 2, CH CH CH ), 2.25–
δ
3
2
2
2.32 (dt, 2, CHCH2CH2), 2.37–2.42 (t, 2, J = 4.29 Hz, 2,
CH2CO2CH3), 3.69 (s, 3, E-OCH3), 3.94 (s, 3, Z-OCH3),
6.22 (m, 1, PhCH=CH), 6.39 (m, 1, PhCH=CH), 7.31–7.36
(m, 5, Ar).
Acyloin reaction of 12a
Sodium metal (0.64 g, 28 mmol) and toluene (100 mL)
were refluxed for 1 h with vigorous stirring, and ethyl hex-5-
enoate (7j) (12a, 0.20 g, 20 mmol) in toluene (10 mL) was
added dropwise over 20 min, and stirred a further 2 h. The
solution was cooled and MeOH (15 mL) was added, the
mixture was poured into water–EtOAc and acidified with
10% HCl, extracted with EtOAc, washed with water and
NaHCO3, dried, and concentrated. Chromatography (hexane–
EtOAc, 7:3) gave 13a (7-hydroxydodeca-1,11-diene-6-one,
2.08 g, 76%). IR (CDCl3) (cm–1): 1707, 3519. 1H NMR
(400 MHz, CDCl3) δ: 1.61–1.82 (m, 6, CH2CH2CH2 and
CHOHCH2), 2.04–2.18 (m, 4 C=CHCH2), 2.40 (t, 2, J =
7.4 Hz, CH2CO), 4.96–5.09 (m, 4, CH2=C), 5.75–5.85 (m, 2
CH2=CH). 13C NMR (100 MHz, CDCl3) δ: 23.0, 23.9, 33.2,
33.5, 33.9, 38.9, 77.6 (CHOH), 115.1, 115.8, 137.7, 138.5,
180.1 (CO). EI-MS m/z: 196 (M+), 182, 169, 167, 149, 125,
107, 99, 97, 81, 69, 55. HR-EI-MS m/z calcd. for C6H9O:
97.0656; found: 97.0653.
6-Phenyl-5-hexenoic acid (7b)
4-Carboxybutyltriphenylphosphonium bromide (2.0 g,
4.5 mmol) in dry THF (6 mL), under nitrogen, was treated
with lithium hexamethyldisilazide (1.8 mL, 9.48 mmol). Af-
© 2003 NRC Canada

Henry-Riyad and Tidwell
703
(400 MHz, CDCl3) δ: 1.81–1.94 (m, 4, CH2CH2CH2), 2.37–
2.41 (m, 4, CHCH2CH2), 2.43 (t, 4, CH2CH2CO), J =
7.6 Hz), 5.61–5.72 (m, Z-PhCH=CH), 6.18–6.28 (m, E-
PhCH=CH), 6.40–6.58 (m, 2, PhCH=CH), 7.17–7.45 (m, 10,
Ar). 13C NMR (100 MHz, CDCl3) δ: 24.5, 29.9, 32.5, 126.2,
127.4, 128.2, 128.4, 128.7, 129.6, 130.5, 131.2, 197.0 (CO).
EI-MS m/z: 243 (M+ – Ph-CH=CH), 215 (M+ – C10H11), 202
(M+ – C11H13), 190 (M+ – C12H13), 174 (M+ – C12H13O),
146 (M+ – C13H13O2), 130, 117, 105, 91, 77. HR-EI-MS m/z
calcd. for C16H19O2: 243.1177; found: 243.1192.2
Oxidation of 13a
Pyridinium chlorochromate (1.6 g, 7 mmol) and 13a
(1.0 g, 5.1 mmol) in CH2Cl2 (20 mL) were heated at reflux
for 1.5 h. The mixture was filtered through Celite, washed
with ether, and the filtrate was concentrated. Chromatogra-
phy (hexane–EtOAc, 7:3) gave dodeca-1,11-diene-6,7-dione
(14a) as a yellow oil (0.44 g, 2.3 mmol, 45%). IR (CDCl3)
1
(cm–1): 1711. H NMR (400 MHz, CDCl3) δ: 1.63–1.78 (m,
4, CH2CH2CH2), 2.08–2.19 (m, 4, CHCH2), 2.37 (t, 4, J =
7.2 Hz, CH2CO), 4.98–5.12 (m, 4, CH2=CH), 5.77–5.83 (m,
2, CH2=CH). 13C NMR (100 MHz, CDCl3) δ: 24,6, 34.5,
52.0, 115.8, 138.7, 200.0 (CO). EI-MS m/z: 195 (MH+), 167,
153, 149, 140, 125, 97, 81, 69, 55. HR-EI-MS m/z calcd. for
C12H19O2: 195.1380; found: 195.1385.
Acknowledgements
Financial support by the Natural Sciences and Engi-
neering Research Council of Canada, The Petroleum Re-
search Fund administered by the American Chemical
Society, and the Killam Foundation for the Arts for a Fel-
lowship to T.T.T. is gratefully acknowledged.
Acyloin reaction of 12b
Sodium metal (0.2 g, 8.6 mmol) and toluene (20 mL)
were heated to reflux with vigorous stirring for 1 h. To this
was added methyl 6-phenylhex-5-enoate (12b, 0.88 g,
4.3 mmol) in toluene (10 mL) dropwise over 20 min.
Stirring was continued for a further 2 h. The solution was
cooled and MeOH (2 mL) was added. The mixture was
poured into water–EtOAc and acidified with 10% HCl, ex-
tracted with EtOAc, washed with water and NaHCO3, dried,
and concentrated. Chromatography (hexane–EtOAc, 7:3) af-
forded the cyclized product cis-15 (7j) as a colourless oil
(0.32 g, 1.8 mmol, 42%). IR (CDCl3) (cm–1): 3608. 1H NMR
(400 MHz, CDCl3) δ: 1.25–2.14 (m, 8, 3CH2, CHCH2Ph,
and OH), 2.52–2.57 (m, 1, CHHAr), 2.74–2.79 (m, 1,
CHHAr), 3.90–3.93 (m, 1, CHOH), 7.28–7.37 (m, 4, Ar).
13C NMR (100 MHz, CDCl3) δ: 21.7, 30.1, 34.4, 40.0, 50.1,
78.8 (CHOH), 126.2, 128.5, 128.6, 129.1, 141.3. EI-MS
m/z:176 (M+), 158 (M+ – H2O), 143, 129, 117, 104, 98, 85,
67, 57. HR-EI-MS m/z calcd. for C12H16O: 176.1199; found:
176.1201. 1,12-Diphenyl-7-hydroxy-dodeca-1,11-dien-6-one
(13b) was obtained as a yellow oil (0.31 g, 21%) 78:22 dou-
ble bonds of E/Z isomers. IR (CDCl3) (cm–1): 1705, 3522.
1H NMR (400 MHz, CDCl3) δ: 1.79–1.84 (m, 6,
2CH2CH2CH2 and CHOHCH2), 2.24–2.28 (m, 2,
CH2CH2CO), 2.33–2.36 (m, 4, 2CHCH2CH2), 5.59–5.63 (m,
Z-PhCH=CH), 6.17–6.23 (m, E-PhCH=CH), 6.38–6.44 (m,
2, 2PhCH=CH), 7.21–7.39 (m, 10, Ar). 13C NMR
(100 MHz, CDCl3) δ: 24.5, 27.4, 28.7, 32.4, 33.5, 37.5, 50.2,
79.4 (CHOH), 126.2, 127.3, 128.4, 128.6, 128.7, 128.9,
129.6, 130.4, 131.2, 133.9, 137.8, 179.6 (CO). EI-MS
m/z:244 (M+ – PhCH=CH), 210, 190, 130, 117, 105, 91, 77.
HR-EI-MS m/z calcd. for C16H22O2: 244.1456; found:
244.1454.
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1
2 Supplementary data (1H NMR spectra) may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National
Research Council Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electroni-
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