Nitroxyl radical reactions with 4-pentenyl- and cyclopropylketenes: New routes to 5-hexenyl- and cyclopropylmethyl radicals

Article abstract of DOI:10.1021/jo0102922

4-Pentenylketenes 4a and 9 and cyclopropylketenes 3a, 13, 14 (RCH=C=O) are generated by photochemical Wolff rearrangements and observed by IR as relatively long-lived species at room temperature in hydrocarbon solvents. The reactions of these ketenes with the nitroxyl radicals tetramethylpiperidinyloxyl (TEMPO, TO?) and tetramethylisoindoline-2-oxyl (TMIO, IO?) form carboxy substituted 5-hexenyl and cyclopropylmethyl radicals which are either trapped by a second nitroxyl radical or undergo rearrangements followed by trapping. The rate constant of the reaction of 4a with TEMPO was similar to that of n-BuCH=C=O (1b), while 3a was 4.3 times more reactive, indicating cyclopropyl stabilization of the incipient radical.

Full text of DOI:10.1021/jo0102922

J . Org. Chem. 2001, 66, 5759-5765
5759
Nitr oxyl Ra d ica l Rea ction s w ith 4-P en ten yl- a n d
Cyclop r op ylk eten es: New Rou tes to 5-Hexen yl- a n d
Cyclop r op ylm eth yl Ra d ica ls
Annette D. Allen, Michael F. Fenwick, Huda Henry-Riyad, and Thomas T. Tidwell*
Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6 Canada
ttidwell@chem.utoronto.ca
Received March 16, 2001
4-Pentenylketenes 4a and 9 and cyclopropylketenes 3a , 13, 14 (RCHdCdO) are generated by
photochemical Wolff rearrangements and observed by IR as relatively long-lived species at room
temperature in hydrocarbon solvents. The reactions of these ketenes with the nitroxyl radicals
tetramethylpiperidinyloxyl (TEMPO, TO•) and tetramethylisoindoline-2-oxyl (TMIO, IO•) form
carboxy substituted 5-hexenyl and cyclopropylmethyl radicals which are either trapped by a second
nitroxyl radical or undergo rearrangements followed by trapping. The rate constant of the reaction
of 4a with TEMPO was similar to that of n-BuCHdCdO (1b), while 3a was 4.3 times more reactive,
indicating cyclopropyl stabilization of the incipient radical.
Recent theoretical1a,b and experimental1b-f studies in
our laboratory have shown that ketenes 1 react with the
aminoxyl radical tetramethylpiperidinyloxyl (TEMPO,
TO•) by initial attack at the ketenyl carbon forming
R-acyl radicals 2, which then typically react with a second
TEMPO molecule (eq 1), sometimes with rearrangement.
This pathway is in accord with the prediction of molec-
ular orbital calculations,1a,b,g,h and is supported by the
effect of the substituents R on the reactivity, including a
qualitative correlation (eq 2) of the rate constants for
reaction with TEMPO with the corresponding rate con-
stants for hydration of the same ketenes in H2O.1c,d
4-pentenyl group which may undergo cyclization3 or a
cyclopropyl group which may undergo ring opening.4 Both
of these reactions are of widespread utility in free radical
chemistry. In previous investigations we have studied the
preparation and reactivity of cyclopropylketenes 3,5 while
4-pentenylketenes have been found to undergo thermal
intramolecular cycloadditions in some cases (eq 3).6 There
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ments. In Rearrangements in Ground and Excited States; Academic
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M. J . Org. Chem. 1998, 63, 8609-8613.
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Chem. 1991, 69, 138-145. (b) Allen, A. D.; Gong, L.; Tidwell, T. T. J .
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Kregse, A. J .; McAllister, M. A.; Tidwell, T. T. J . Am, Chem. Soc. 1992,
114, 1878-1879.
This reaction provides a new method for forming
radicals 2 with functional groups in the side chain R that
may interact with the carbon centered radical generated
in 2.2 The current study involves ketenes 1 where R is a
(1) (a) Sung, K.; Tidwell, T. T. J . Org. Chem. 1998, 63, 9690-9697.
(b) Huang, W.; Henry-Riyad, H.; Tidwell, T. T. J . Am. Chem. Soc. 1999,
121, 3939-3943. (c) Allen, A. D.; Cheng, B.; Fenwick, N. H.; Huang,
W.; Missiha, S.; Tahmassebi, D.; Tidwell, T. T. Organic Lett. 1999, 1,
693-696. (d) Allen, A. D.; Cheng, B.; Fenwick, M. F.; Givehchi, B.;
Henry-Riyad, H.; Nikolaev, V. A.; Shikova, E. A.; Tahmassebi, D.;
Tidwell, T. T.; Wang, S. J . Org. Chem. 2001, 66, 2611-2617. (e) Carter,
J .; Fenwick, M. H.; Huang, W.; Popik, V. V.; Tidwell, T. T. Can. J .
Chem. 1999, 77, 806-809. (f) Allen, A. D.; Henry-Riyad, H.; Porter,
J .; Tahmassebi, D.; Tidwell, T. T. J . Org. Chem., in press. (g) Hou, H.;
Wang, B.; Gu, Y. J . Phys. Chem. A 2000, 104, 320-328. (h) Hou, H.;
Wang, B.; Gu, Y. Phys. Chem. Chem. Phys. 2000, 2, 2329-2334.
10.1021/jo0102922 CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/28/2001

5760 J . Org. Chem., Vol. 66, No. 17, 2001
Allen et al.
have however been no previous studies of free radical
reactions of such ketenes.
to formation of the corresponding radicals substituted by
H or alkyl. Reaction of TMIO with CH2)CHCN and with
CH2)CHCO2Et also occurs at 110 °C forming the prod-
ucts of 1,2-addition of two TMIO radicals.12g
The trapping reactions of radicals by nitroxyls such as
TEMPO have widespread application7,8 and other ni-
troxyl radicals have also been used for this purpose, for
example 1,1,3,3-tetramethylisoindoline-2-yloxyl (TMIO)9
and (CF3)2NO•.10 The relative reactivities of TMIO
compared to TEMPO range from 1.04 to 1.99b toward a
number of radicals, with the greater selectivities for less
reactive radicals. The radical TMIO• has the advantages
relative to TEMPO that it is usually more readily
separated from reaction products by chromatography,
and the addition products from this radical also possess
a UV chromophore that aids in spectral analysis. A
disadvantage is that this radical is not commercially
available. The radical (CF3)2NO• forms a 1,2-diadduct
with Ph2CdCdO,10d but is less convenient to prepare, and
is also highly volatile so that more care is needed in
handling.
Beckwith and Bowry4b estimated a rate ratio of kH/
kCO Bu-t ) 20-50 for ring opening in cyclohexane of the
2
parent cyclopropylmethyl radical relative to 5a (eq 4).
However, cyclization of 6,6-diphenylhexenyl radicals 6
showed no change in the rate constant for CO2Et or CN
relative to H (eq 6).11
Later studies by Horner, Tanaka, and Newcomb4c
showed that in THF solvent at 20 °C that for 7 the rate
As shown in eq 1 addition of TEMPO to a ketene forms
a radical adjacent to an acyloxy group, and such radicals
formed by abstraction reactions3c-g or by oxidation of
enolates7c have been applied in synthesis. R-Acyl groups
stabilize carbon-centered radicals.4c,11 Thus the formation
of carbon centered radicals substituted with R-CO2R or
R-CN groups by radical additions to acrylate esters and
acrylonitrile,12a,b cyclization of 6-cyano-5-hexenyl radicals3a,b
and cyclization of radical 5b (eq 4),12c and by ring opening
of 2-carboalkoxyl substituted cyclopropyl radicals 5c (eq
5)12d,e are strongly accelerated by factors of 103 relative
ratio kH/kCO Et was only 1.1. However while the solvent
effect on the ring opening of 7a was negligible the rate
2
ratio kCH CN/kTHF for 7b was 1.8 at 20 °C, and this
3
acceleration in the reaction of the ester substituted
substrate in the more polar solvent suggests that in
hydrocarbon solvents a larger kH/kCO R rate ratio might
2
be anticipated. The conjugative stabilization of the acry-
late esters formed by ring opening of 5a and 7b is cited
as one cause of the facility of this process.4c
Resu lts
Because of the significant influence of carboalkoxy
substituents on radical rearrangements as outlined above
and because of our discovery1a-f of the generality of
aminoxyl addition to ketenes we have undertaken a
systematic study of the reactions of aminoxyl radicals
with ketenes bearing cyclopropyl and alkenyl side chains
and the examination of the reactions of the substituted
R-acyl radicals formed. 1-Diazo-6-hepten-2-one (8a )13a,b
was prepared by reaction of the acyl chloride with
diazomethane as has been described.13 1-Diazo-7-phenyl-
6-hepten-2-one (8b)13b was prepared similarly from the
acyl chloride of the acid obtained by the reaction of the
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Ghosez, L.; Ernst, B.; Greuter, H. J . Am. Chem. Soc. 1985, 107, 2192-
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107, 4339-4341. (c) Snider, B. B. Chem. Rev. 1988, 88, 793-811. (d)
Tidwell, T. T. Ketenes; J ohn Wiley: New York, 1995; pp 554-564.
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Thang, S. H.; Suyama, S. J . Org. Chem. 2000, 65, 16-23. (b) Benoit,
D.; Chaplinski, V.; Braslau, R.; Hawker, C. J . J . Am. Chem. Soc. 1999,
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N.; Howden, R. K.; Mahal, L. K. Macromolecules 1997, 30, 6445-6550.
(d) Kothe, T.; Marque, S.; Martschke, R.; Popov, M.; Fischer, H. J .
Chem. Soc., Perkin Trans. 2 1998, 1553-1559. (e) J ahn, U. J . Org.
Chem. 1998, 63, 7130-7131.
(8) (a) Georges, M. K.; Veregin, R. P. N.; Kazmaier, P. M.; Hamer,
G. K. Macromolecules 1993, 26, 2987-2988. (b) Hawker, C. J . Acc.
Chem. Res. 1997, 30, 373-382. (c) Nakamura, T.; Busfield, W. K.;
J enkins, I. D.; Rizzardo, E.; Thang S. H.; Suyama, S. J . Am. Chem.
Soc. 1997, 119, 10987-10991. (d) Patten, T. E.; Matyjaszewski, K. Acc.
Chem. Res. 1999, 32, 895-903.
(9) (a) Beckwith, A. L. J .; Bowry, V. W.; Ingold, K. U. J . Am. Chem.
Soc. 1992, 114, 4983-4992. (b) Bowry, V. W.; Ingold, K. U. J . Am.
Chem. Soc. 1992, 114, 4992-4996. (c) Beckwith, A. L. J .; Bowry, V.
W.; Moad, G. J . Org. Chem. 1988, 53, 1632-1641.
(10) (a) Doba, T.; Ingold, K. U. J . Am. Chem. Soc. 1984, 106, 3958-
3963. (b) Anpo, M.; Chatgilialoglu, C.; Ingold, K. U. J . Org. Chem. 1983,
48, 4104-4106. (c) Malatesta, V.; Ingold, K. U. J . Am. Chem. Soc. 1981,
103, 3094-3098. (d) Banks, R E.; Haszeldine, R. N.; Murray, M. B. J .
Fluorine Chem. 1981, 17, 561-564.
(11) Newcomb, M.; Horner, J . H.; Filipkowski, M. A.; Ha, C.; Park,
S.-U. J . Am. Chem. Soc. 1995, 117, 3674-3684.
(12) (a) Giese, B. Angew. Chem., Int. Ed. Engl. 1983, 22, 753-764.
(b) Caronna, T.; Citterio, A.; Ghirardini, M.; Minisci, F. Tetrahedron
1977, 33, 793-796. (c) Effio, A.; Griller, D.; Ingold, K. U.; Beckwith,
A. L. J .; Serelis, A. K. J . Am. Chem. Soc. 1980, 102, 1734-1736. (d)
Beckwith, A. L. J .; Bowry, V. W. J . Org. Chem. 1989, 54, 2681-2688.
(e) Newcomb, M.; Choi, S.-Y. Tetrahedron Lett. 1993, 34, 6363-6364.
(f) Choi, S.-Y.; Newcomb, M. Tetrahedron 1995, 51, 657-664. (g)
Aldabbagh, F.; Busfield, W. K.; J enkins, I. D.; Thang, S. H. Tetrahedron
Lett. 2000, 41, 3673-3676.
(13) (a) Ceccherelli, P.; Curini, M.; Marcotullio, M. C.; Rosati, O.
Tetrahedron 1992, 48, 9767-9774. (b) Fawzi, M. M.; Gutsche, C. D. J .
Org. Chem. 1966, 31, 1390-1393. (c) Rey, M. d. l. A.; Mart´ınez-Pe´rez,
J . A.; Ferna´ndez-Gacio, A.; Halkes, K.; Fall, Y.; Granja, J .; Mourino,
A. J . Org. Chem. 1999, 64, 3196-3206. (d) Hart, D. J .; Kanai, K.;
Thomas, D. G.; Yang, T.-K. J . Org. Chem. 1983, 48, 289-294. (e)
J uaristi, E.; J ime´nez-Va´zquez, H. A. J . Org. Chem. 1991, 56, 1623-
1630.

Nitroxyl Radical Reactions
J . Org. Chem., Vol. 66, No. 17, 2001 5761
Wittig reagent13c derived from 5-bromovaleric acid with
benzaldehyde as an 87/13 E/Z mixture (eq 7). The
cyclopropyl diazo ketones 8c-e were also prepared from
the corresponding acyl chlorides by reaction with diazo-
methane.
Ta ble 1. Ra te Con sta n ts for Keten e Rea ction s w ith
Am in oxyl Ra d ica ls in Isoocta n e a t 25 °C
ketene
radical k2 (M-1 s-1
)
krel
PhCHdCdO (1a )
IO•
6.99 × 10-1 1.0 × 103
TO•
IO•
1.26a
1.0 × 103
n-BuCHdCdO (1b)
6.95 × 10-4 1.0
1.22 × 10-3b 1.0
5.26 × 10-3 4.3
1.89 × 10-3 1.6
TO•
TO•
TO•
c-PrCHdCdO (3a )
CH2dCH(CH2)3CHdCdO (4a )
a
b
Ref 1c. Ref 1d.
mixture of E-20a and E,E-21 (55%). Similarly 14 gave
24a (Z, 6%; E, 18%) after chromatography. The substit-
uents in 20a and 23 evidently promote elimination.
Rates for the reaction of 3a and 4a with excess TEMPO
in isooctane were measured by observing the decrease
in the ketene absorption by UV spectroscopy as we have
reported previously,1c,d and the derived rate constants are
reported in Table 1.
Because of the utility of the tetramethylisoindoline-2-
oxyl radical (TMIO, IO•) the reactions of this radical with
ketenes were also studied. Phenylketene (1a ) and n-
butylketene (1b) were generated in pentane by photolysis
of the corresponding diazo ketones and addition of IO•
resulted in the isolation of the 1,2-bis(addition) products
25a ,b, in 30 and 38% yield, respectively. Based on
previous studies using TEMPO these reactions proceed
by initial attack at the carbonyl carbon of the ketene (eq
10). The kinetics of these reactions in isooctane were
measured by observing the decrease of the ketene ab-
sorption by UV in the presence of excess TMIO, and the
derived rate constants are given in Table 1.
Photolysis of the 5-pentenyl and 6-phenyl-5-pentenyl
diazo ketones (8a ,b, respectively) in pentane with 250
nm light gave the ketenes 4a and 9 as identified by their
IR bands at 2120.5 and 2119.5 cm-1, respectively. Addi-
tion of 2.1 equivalents of TEMPO to the preformed
ketenes 4a and 9 to form the radicals 10a ,b gave the 1,2-
diaddition products (11a ,b) in 63 and 67% yields, respec-
tively, after chromatography (eq 8). Cyclobutanone prod-
ucts from ketene cyclization or cyclopentane products
from radical cyclization were not detected.
Cyclization of 11a was achieved using the method of
Studer,3f who found heating of the 5-hexenyl-1-phenyl
substituted TEMPO substituted adduct 11c gave even-
tual cyclization to 12b of the reversibly formed 5-hexenyl
radical. For 11a this gave the cyclized product 12a (74%)
as a cis/trans mixture (eq 9). However, this procedure
lacks generality as comparable treatment of 11b did not
give a cyclized product, but instead gave more complex
reactions. The thermal reactivities of 11b and other bis-
(TEMPO) adducts of ketenes are under investigation.
The reactions of TMIO with cyclopropylketene (3a ) at
25 °C with analysis of the initial product mixture by H
1
NMR showed the ring closed and ring opened products
17b and 18b were formed in a 2/1 ratio, whereas reaction
at 50 °C gave a product ratio of 1/2. Separation of the
product from reaction at 50 °C gave the ring closed and
ring opened products 17b (29%) and E-18b (8%). The
inefficient isolation of E-18b is due to difficulties with
the chromatographic separation. Reaction of TMIO with
13 at 25 °C gave after chromatography the ring opened
Z-20b (14%) and E-20b (25%), without diene product
from elimination. Reaction of 14 with TMIO at 25 °C gave
after chromatography the elimination products Z-24b
(7%) and E-24b (53%). The identification of the products
followed from their spectral properties, including COSY,
HSQC, TOCSY, and HMBC NMR studies of 20.
Cyclopropylketene (3a), trans-2-phenylcyclopropylketene
(13), and 2,2-dimethylcyclopropylketene (14) were gener-
ated by photolysis of the corresponding diazo ketones, and
identified by their IR bands at 2120, 2121, and 2119 cm-1
,
respectively. Addition of TEMPO to 3a at 25 °C gave the
ring closed and ring opened adducts 17a and 18a in a
1/1.6 ratio (Scheme). Upon chromatography 17a (7%) and
E/Z-18a (11%) were isolated. Reaction of 13 gave only
ring opened adducts, which upon chromatography gave
the elimination product 2-Z,4-E-21, Z-20a (14%), and a
Discu ssion
The rate constants for ring opening of the cyclopropyl-
methyl radical4c and ring closure of the 5-hexenyl radical
are reported as 4.0 × 108 s-1 at 20 °C, essentially
independent of solvent, and 2.3 × 105 s-1, respectively.

5762 J . Org. Chem., Vol. 66, No. 17, 2001
Allen et al.
The capture of the 4-pentenylketene 4a by TEMPO to
give the uncyclized adduct 11a of addition of two TEMPO
molecules (eq 8) demonstrates that capture of the radical
10a is faster than cyclization. However 11a was isomer-
ized to the cyclized adduct 12a (eq 9), showing that 10a
is formed reversibly and can undergo cyclization to form
12a . However the failure of the 5-phenyl adduct 11b to
give a cyclized product is indicative of a more complicated
reaction pathway, and this is currently under investiga-
tion.
For the cyclopropylketene 3a the competitive formation
of ring-closed adducts 17 and ring opened adducts 18
indicates the rate of capture of the initial radicals 15 and
the rate of irreversible ring opening (Scheme 1) are finely
balanced. As noted above the reaction of 3a with TMIO
gave a higher proportion of ring closed product, showing
that TMIO was moderately more reactive toward the
intermediate acyl radical than is TEMPO. This agrees
with the absolute rate data noted above.9b
The presence of radical stabilizing groups on the
cyclopropyl rings in 13 and 14 changes the reaction to
complete ring opening in both cases. This is expected
because of the significant acceleration of cyclopropyl ring
opening which has been found for phenyl and methyl
groups.
F igu r e 1. Plot of log k2(TEMPO) vs log kH for ketenes with
points for 3a and 4a .
O
2
In summary the reactions of aminoxyl radicals with
4-pentenyl- and cyclopropylketenes have been demon-
strated and provide a new route to carboxy substituted
4-pentenyl and cyclopropylmethyl radicals which undergo
the characteristic ring closing and ring opening reactions,
respectively, of these substrates. The kinetics of the
reactions of n-butyl, 4-pentenyl-, and cyclopropylketenes
with aminoxyl radicals have been measured and the rate
constants confirm that the reactions proceed with initial
radical attack on the carbonyl carbon, with a moderate
rate enhancing effect of cyclopropyl due to its stabiliza-
tion of the R-acyl radical.
The ratio of ring closed to ring opened products of the
cyclopropylmethyl radicals 15 was 1/1.6 for capture by
TEMPO at 25 °C but 2/1 for TMIO, suggesting that TMIO
is more efficient at capturing the initial radical than is
TEMPO. For the 2-phenylcyclopropylmethyl radicals 19
only ring opening was observed in both cases, consistent
with the acceleration of ring opening by the phenyl on
the cyclopropyl ring.
The rate constants for the addition of TEMPO to
phenylketene (1a ) and n-butylketene (1b) exceed those
for the corresponding reactions of TMIO by a factor of
1.8 in both cases (Table 1). This differs from the greater
reactivity of TMIO compared to TEMPO in reactions with
radicals noted above, and by others.9b A possible explana-
tion of this reversal is that the reaction with ketenes has
a later transition state and the more rigid TMIO suffers
from steric crowding.
The relative rate constants for the reaction of ketenes
RCHdCdO with TEMPO for R ) Ph,1c c-Pr, CH2)CHCH2-
CH2, and n-Bu are 1.0 × 103, 4.3, 1.6, and 1.0, respec-
tively. The strong acceleration by Ph is expected because
of the conjugative ability of this group in stabilizing the
resultant radical. Cyclopropyl groups are known to
stabilize free radicals,14 and the effect of the c-Pr group
on the addition of TEMPO to ketene demonstrates a
small but significant accelerating effect. The 4-pentenyl
and n-butyl substituted ketenes have similar reactivities,
as expected.
The rate constant for hydration of c-PrCHdCdO (3a )
has been reported previously,5c and on the assumption
that the rate constant for hydration of 4-pentenylketene
(4a ) is similar to that of n-butyl ketene (1b) then the
reactivities of both 3a and 4a can be fit to the previous
correlation of TEMPO and H2O reactivities with ketenes
(eq 2),1c,d as shown in Figure 1. The reasonable fit of these
values to the plot lends confidence in the predictive value
of this correlation.
Exp er im en ta l Section
Glassware was oven-dried (140 °C) overnight while all
plastic equipment and microliter syringes were kept in a
desiccator. All ketene reactions were carried out in solutions
degassed with argon or nitrogen. Ether and toluene were
distilled from Na/benzophenone just prior to use. Dichlo-
romethane, pentane and 2,2,4-trimethylpentane were all
stored over 4 Å molecular sieves. Deuterated chloroform was
kept over potassium carbonate. All other solvents and reagents
were used as received. 1,1,3,3-Tetramethylisoindolin-2-yloxy
(TMIO) was prepared as described15 (see Supporting Informa-
tion). Photolyses of diazo ketones were carried out in a Rayonet
reactor using lamps of wavelengths chosen based on the
absorption spectra of the substrates and products.
1-Dia zo-6-h ep ten -2-on e (8a ).13a 5-Hexenoyl chloride (0.61
g, 5.0 mmol) from the acid13e in 5 mL ether was added dropwise
over 0.5 h to stirring cooled diazomethane (12.5 mmol, 2.5
equiv.) in 60 mL of ether, and left stirring cold for an additional
2 h. The excess diazomethane was evaporated and quenched
in acetic acid, and the solution was concentrated. Chromatog-
raphy (30% EtOAc/hexane) gave 8a (0.42 g, 61%) as a yellow
oil. 1H NMR (CDCl3) δ 1.73 (q, 2), 2.08 (dt, 2), 2.33 (t, 2), 4.97-
5.06 (m, 2), 5.22 (s, 1), 5.70-5.82 (m, 1). IR (pentane) 2106,
1666 cm-1
.
Rea ction of 4-P en ten ylk eten e (4a ) w ith TEMP O. 1-Di-
azo-6-hepten-2-one (10 mg, 0.072 mmol) in 25 mL of pentane
was photolyzed 1 min with 250 nm light to give 4a , IR 2120.5
(14) Tidwell, T. T. Conjugative and Substituent Properties of the
Cyclopropyl Group. In Chemistry of the Cyclopropyl Group; Rappoport,
Z., Ed.; Wiley: New York, 1987; Chapter 1, 565-632.
(15) (a) Griffiths, P. G., Moad, G., Rizzardo, E., Solomon, D. H. Aust.
J . Chem. 1983, 36, 397-401. (b) Micallef, S. A. J . Chem. Soc., Perkin
Trans. 1 1999, 65-72.

Nitroxyl Radical Reactions
J . Org. Chem., Vol. 66, No. 17, 2001 5763
Sch em e 1
cm-1. TEMPO (30 mg, 0.18 mmol) was added and the solution
stirred 31 h at 25 °C. Chromatography (15% EtOAc/hexane)
gave 11a (19 mg, 63%). 1H NMR (CDCl3) δ 1.02-2.11 (m, 42),
4.47 (t, 1), 4.93-5.03 (m, 2), 5.22 (s, 1), 5.75-5.82 (m, 1). 13C
NMR (CDCl3) δ 17.2, 20.8, 34.0, 40.7, 60.5, 83.6, 115.1, 138.6,
149.9, 171.9. EIMS m/z 423 (MH+), 266, 156, 140, 97, 83. IR
and stirred 16 h. The pentane was evaporated and chromato-
graphed (5% EtOAc/hexane) yielding 25a (15 mg, 0.030 mmol,
1
30%) mp 133-135 °C. H NMR (CDCl3) δ 1.10 (s, 3), 1.21 (s,
3), 1.37 (s, 6), 1.51 (s, 3), 1.59 (s, 3), 1.64 (s, 3), 5.49 (s, 1),
7.0-7.6 (m, 13). 13C NMR (CDCl3) δ 25.2, 25.4, 29.9, 30.3, 67.9,
68.2, 86.6, 121.4, 121.6, 127.2, 127.3, 127.5, 127.6, 128.5, 128.6,
137.2, 143.9, 144.5, 145.0, 171.4. IR (CDCl3) 1779 cm-1. EIMS
m/z 499 (1), 308 (5), 190 (100), 174 (59). HREIMS m/z calcd
for C32H39N2O3 499.2961, found 499.2947.
(pentane) 1785 cm-1
.
Isom er iza tion of 11a . A solution of 11a (20 mg, 0.047
mmol) in 4 mL t-BuOH under argon was heated 24 h at 130
°C. The solvent was evaporated and chromatography (9/1
CHCl3/MeOH) gave 12a (15 mg, 74%) as a 55/45 cis/trans
mixture. 1H NMR (CDCl3) δ 0.9-2.5 (m, 48), 2.62-2.70 (m,
1), 2.86-2.93 (m 1), 3.68-3.76 (m, 2), 3.86-3.94 (m, 2). 13C
NMR (CDCl3) δ 17.26, 17.3, 20.6, 20.8, 25.6, 28.8. 29.3, 29.9,
30.1, 30.4, 33.0, 33.5, 39.9, 40.0, 42.7, 42.73, 45.8, 48.5, 60.1,
60.4, 80.4, 95.7, 178.1. EIMS m/z 423, 284, 185, 142, 93. IR
Gen er a tion of n -Bu tylk eten e (1b) a n d Tr a p p in g w ith
TMIO. 1-Diazo-2-hexanone (20 mg, 0.16 mmol) in 10 mL of
pentane was irradiated for 10 min with 250 nm light and then
TMIO (86 mg, 0.45 mmol) was added at room temperature and
the solution stirred for 18 h. The pentane was evaporated and
the residue chromatographed (20% EtOAc/hexane) yielding
25b (31 mg, 0.067 mmol, 38%) as pale yellow crystals, mp 122-
(pentane) 1749 cm-1
.
125 °C. H NMR (CDCl3) δ 0.95 (t, 3, J ) 5.7 Hz), 1.36-1.70
1
1-Dia zo-7-p h en yl-6-h ep ten -2-on e (8b).13b 6-Phenyl-5-hex-
enoyl chloride (0.80 g, 4.0 mmol) in 5 mL ether and added over
0.5 h to a stirring cooled solution of diazomethane (0.125 mol)
in 60 mL of ether and stirred cold 2 h. Excess diazomethane
was evaporated and quenched in acetic acid, and the remaining
solution was concentrated. Chromatography (3/7 EtOAc/hex-
ane) gave 8b (87/13 E/Z mixture, 0.65 g, 75%) as a yellow oil.
1H NMR (CDCl3) δ 1.84 (q, 2), 2.25 (dt, 2), 2.37 (t, 2), 5.22 (s,
1), 5.63 (m, 1), 6.19 (m, 1), 6.40 (m, 1), 7.30-7.33 (m, 5). IR
(m, 28), 1.82-2.04 (m, 2), 4.61 (t, 1, J ) 4.8 Hz), 7.1-7.4 (m,
8). 13C NMR (CDCl3) δ 13.9, 14.1, 15.3, 22.6, 22.8, 25.3, 25.7,
27.6, 28.8, 30.0, 31.3, 31.6, 32.7, 65.8, 68.2, 68.3, 68.4, 82.9,
121.3, 121.5, 127.2, 127.3, 127.5, 173.2. IR (CDCl3) 1776 cm-1
.
EIMS m/z 479 (0.02), 288 (16), 190 (19), 174 (100). HREIMS
m/z calcd for C30H43N2O3 479.3274, found 479.3262.
Gen er a tion of Cyclop r op ylk eten e (3a ) a n d Tr a p p in g
w ith TEMP O. Cyclopropyl diazomethyl ketone (8c, 86 mg,
0.78 mmol) in 60 mL pentane was irradiated for 10 min with
250 nm light and TEMPO (265 mg, 1.7 mmol) was added at
room temperature and the solution stirred for 18 h. The
pentane was evaporated and excess TEMPO was removed by
Kugelrohr distillation. Chromatography (CH2Cl2) gave 17a (22
mg, 0.06 mmol, 7%) as an orange oil. Further elution (2%
MeOH in CH2Cl2) gave a mixture of 18a -E/Z (32 mg, 0.08
mmol, 11%) as an orange oil. 17a : 1H NMR (CDCl3) δ 0.30-
0.38 (m, 1), 0.52-0.58 (m, 1), 0.64-0.78 (m, 2), 1.1-1.8 (m,
37), 3.64 (d, 2, J ) 9.4 Hz). 13C NMR (CDCl3) δ 2.0, 7.9, 14.3,
16.8, 17.0, 19.9, 20.2, 20.4, 20.5, 31.7, 31.8, 33.6, 34.4, 39.0,
40.1, 40.2, 59.6, 59.9, 60.0, 60.5, 89.0, 170.1. IR (CDCl3) 1756
cm-1. EIMS m/z 395 (0.05), 238 (20), 156 (76), 140 (100).
HREIMS m/z calcd for C23H43N2O3 395.3274, found 395.3258.
E-18a : 1H NMR (CDCl3) δ 1.04-1.76 (m, 36), 2.40-2.46 (m,
2), 3.82-3.88 (m, 2), 5.89 (d, 1, J ) 15.5 Hz), 7.02-7.10 (m,
1). 13C NMR (CDCl3) δ 17.2, 17.3, 20.3, 20.8, 29.3, 30.4, 32.1,
32.15, 33.3, 36.8, 39.2, 39.8, 45.4, 55.8, 59.9, 60.0, 60.3, 74.7,
(pentane) 2106, 1666 cm-1
.
R ea ct ion of 5-P h en yl-4-p en t en ylk et en e (9) w it h
TEMP O. 1-Diazo-7-phenyl-6-hepten-2-one (10 mg, 0.047 mmol)
in 25 mL of pentane was photolyzed for 1 min with 250 nm
light to give 9 (IR 2119 cm-1). TEMPO (15 mg, 0.096 mmol)
was added and the solution was stirred 24 h at 25 °C.
Chromatography with CH2Cl2 to remove excess TEMPO and
1
then with Et2O gave 11b (94/6 E/Z mixture, 16 mg, 67%). H
NMR (CDCl3) δ 1.10-2.31 (m, 42), 4.53 (t, 1), 5.63 (m, 1), 6.13-
6.27 (m, 1), 6.39-6.44 (m, 1), 7.29-7.34 (m, 5). 13C NMR
(CDCl3) δ 24.4, 32.6, 33.5, 34.2, 39.8, 40.4, 82.2, 126.1, 126.5,
128.4, 130.3, 171.9. EIMS (m/z) 499 (MH+), 360, 342, 185, 156,
140, 126, 98, 84, 69, 58, 41. IR (pentane) 1772 cm-1
.
Gen er a tion of P h en ylk eten e (1a ) a n d Tr a p p in g w ith
TMIO. Diazoacetophenone (15 mg, 0.10 mmol) in 20 mL
pentane was irradiated for 15 min with 300 and 350 nm light,
and TMIO (55 mg, 0.29 mmol) was added at room temperature

5764 J . Org. Chem., Vol. 66, No. 17, 2001
Allen et al.
121.7, 146.5, 166.6. IR (CDCl3) 1732 cm-1. EIMS m/z 395 (4),
238 (66), 156 (23), 140 (100). HREIMS m/z calcd for C23H43N2O3
395.3274, found 395.3277. Z-18a : 1H NMR (CDCl3) δ 1.04-
1.76 (m, 36), 2.88-2.95 (m, 2), 3.82-3.88 (m, 2), 5.85-5.95 (d,
1), 6.36-6.42 (m, 1). 13C NMR (CDCl3) δ 17.2, 17.3, 20.3, 20.8,
29.3, 30.4, 32.1, 32.15, 33.3, 36.8, 39.2, 39.8, 45.4, 55.8, 59.9,
60.0, 60.3, 75.4, 119.2, 147.8, 177.9. Structural assignments
confirmed by COSY, HSQC, TOCSY, HMBC.
temperature. After evaporation of the pentane, chromatogra-
phy (5% EtOAc/hexane) yielded Z-20b (8 mg, 0.015 mmol, 14%)
as pale white crystals, mp 82-84 °C, and elution with CH2Cl2
afforded E-20b (15 mg, 0.028 mmol, 25%) as pale white
crystals, mp 111-113 °C. E-20b: 1H NMR (CDCl3) δ 0.82 (s,
3), 1.24-1.32 (m, 6), 1.38-1.54 (m, 12), 1.66 (s, 3), 2.68-2.80
(m, 1), 3.04-3.16 (m, 1), 4.90 (t, 1, J ) 14.6 Hz), 6.12 (d, 1, J
) 14.4 Hz), 6.98-7.52 (m, 14). 13C NMR (CDCl3) δ 25.2, 25.7,
28.8, 29.4, 30.0, 39.5, 68.3, 86.5, 121.3, 121.5, 121.6, 121.7,
127.6, 127.65, 128.0, 128.2, 142.3, 144.0, 144.7, 145.1, 146.4,
166.8. IR (CDCl3) 1740 cm-1. EIMS m/z 539 (0.01), 348 (8),
190 (40), 174 (17), 157 (100). HREIMS m/z calcd for C35H43N2O3
(MH+) 539.3274, found 539.3257. Z-20b: 1H NMR (CDCl3) δ
0.83 (s, 3), 1.24-1.70 (m, 21), 3.24-3.36 (m, 1), 3.54-3.70 (m,
1), 4.94 (bs, 1), 6.06 (d, 1, J ) 10.8 Hz), 6.36-6.46 (m, 1), 6.8-
7.4 (m, 13). 13C NMR (CDCl3) δ 25.3, 25.4, 25.7, 28.8, 29.5,
30.0, 35.7, 68.1, 86.6, 119.0, 121.3, 121.5, 121.6, 127.1, 127.2,
Gen er a tion of Cyclop r op ylk eten e (3a ) a n d Tr a p p in g
w ith TMIO. Cyclopropyl diazomethyl ketone (8c, 18 mg, 0.16
mmol) in 20 mL isooctane was irradiated for 7 min with 250
nm light and TMIO (62 mg, 0.33 mmol) was added and the
solution was stirred at 50 °C for 20 h. After evaporation of
the isooctane chromatography (5% EtOAc/hexane) gave 17b,
mp 139-140 °C (21 mg, 0.046 mmol, 29%), and further elution
with CH2Cl2 afforded E-18b, mp 91-93 °C (6 mg, 0.012 mmol,
8%). 17b: 1H NMR (CDCl3) δ 0.54-0.98 (m, 4), 1.26-1.70 (m,
24), 3.87 (d, 1, J ) 9.3 Hz), 7.10-7.40 (m, 10). 13C NMR (CDCl3)
δ 2.2, 5.3, 13.7, 25.4, 25.6, 28.7, 29.6, 30.1, 31.4, 68.0, 68.4,
68.7, 87.3, 121.3, 121.5, 121.6, 127.2, 127.3, 127.5, 143.9, 144.7,
145.3, 172.5. IR (CDCl3) 1778 cm-1. EIMS m/z 463 (0.02), 272
(17), 190 (50), 174 (100). HREIMS m/z calcd for C29H39N2O3
463.2961, found 463.2945. E-18b: 1H NMR (CDCl3) δ 1.20-
1.64 (m, 24), 2.56-2.68 (m, 2), 4.08 (t, 2, J ) 5.7 Hz), 6.18 (d,
1, J ) 12.0 Hz), 7.04-7.10 (m, 9). 13C NMR (CDCl3) δ 25.4,
28.8, 32.4, 67.3, 68.3, 75.0, 121.0, 121.4, 121.5, 127.2, 127.6,
144.1, 145.0, 147.2, 167.0. IR (CDCl3) 1744 cm-1. EIMS m/z
463 (6), 272 (25), 190 (13), 174 (56). HREIMS m/z calcd for
127.5, 127.9, 128.1, 144.0, 147.7, 166.7. IR (CDCl3) 1741 cm-1
.
EIMS m/z 539 (0.05), 348 (4), 190 (21), 174 (16), 157 (100).
HREIMS m/z calcd for C35H43N2O3 (MH+) 539.3274, found
539.3294.
Gen er a t ion of 2,2-Dim et h ylcyclop r op ylk et en e (14)
a n d Tr a p p in g w ith TEMP O. 2,2-Dimethylcyclopropyl di-
azomethyl ketone (8e,16b 32 mg, 0.23 mmol) in 40 mL of
pentane was irradiated for 4 min with 250 nm light and
TEMPO (910 mg, 5.83 mmol) was added at room temperature
and the solution stirred for 24 h. The pentane was evaporated
and excess TEMPO removed by Kugelrohr distillation, and
chromatography (10% EtOAc/hexane) gave Z-24a (4 mg, 0.015
mmol, 6%) as white needles (mp 105-108 °C) and then E-24a
(11 mg, 0.041 mmol, 18%) as white crystals (mp 68-71 °C).
Z-24a : 1H NMR (CDCl3) δ 1.06 (s, 6), 1.16 (s, 6), 1.2-1.7 (m,
6), 1.85 (s, 3), 1.9 (s, 3), 5.55-5.65 (bd, 1), 6.85-6.95 (m, 2).
13C NMR (CDCl3) δ 17.3, 18.5, 20.9, 27.2, 32.2, 39.3, 60.1, 113.2,
122.6, 141.2, 146.3, 180.4. IR (CDCl3) 1734 cm-1. EIMS m/z
266 (9), 156 (20), 140 (36), 109 (100), 81 (100). HREIMS m/z
calcd for C16H27NO2 265.2042, found 265.2050. E-24a : 1H
NMR (CDCl3) δ 1.06 (s, 6), 1.17 (s, 6), 1.4-1.8 (m, 6), 1.88 (s,
3), 1.9 (s, 3), 5.80 (d, 1, J ) 15.0 Hz), 6.01 (d, 1, J ) 11.4 Hz),
7.62 (dd, 1, J ) 13.2, 11.4 Hz). 13C NMR (CDCl3) δ 16.9, 18.9,
20.4, 26.4, 31.7, 38.8, 59.9, 116.8, 123.7, 141.3, 146.2, 167.8.
IR (CDCl3) 1732 cm-1. EIMS m/z 265 (2), 156 (5), 109 (100),
81 (31). HREIMS m/z calcd for C16H27NO2 265.2042, found
265.2047.
C
29H39N2O3 (MH+) 463.2961, found 463.2923.
Gen er a tion of 2-P h en yl-1-cyclop r op ylk eten e (13) a n d
Tr a p p in g w ith TEMP O. E-2-Phenyl-1-cyclopropyl diazo-
methyl ketone (8d ,16a 18 mg, 0.097 mmol) in 20 mL pentane
was irradiated 7 min with 250 nm light, and TEMPO (310 mg,
2.0 mmol) was added at room temperature and the solution
was stirred 18 h. The pentane was evaporated and excess
TEMPO was removed by Kugelrohr distillation. Chromatog-
raphy (5% EtOAc/hexane) gave the elimination product 2-Z-
4-E-21a as a white solid, mp 82-84 °C, Z-20a as an orange
oil (6.5 mg, 0.014 mmol, 14%), and a mixture of E,E-21a and
E-20a (25 mg, 0.053 mmol, 55%) as an orange oil that were
separated on further chromatography. Z-20a: 1H NMR (CDCl3)
δ 0.66 (bs, 3), 0.96-1.82 (m, 33), 3.28-3.84 (m, 1), 3.50-3.64
(m, 1), 4.83 (dd, 1, J ) 7.2, 4.8 Hz), 5.70-5.90 (m, 1), 6.06-
6.22 (m, 1), 7.2-7.6 (m, 5). 13C NMR (CDCl3) δ 16.4, 16.5, 19.8,
20.0, 31.2, 33.3, 33.9, 35.0, 38.4, 39.8, 59.2, 85.1, 118.4, 126.5,
127.0, 127.3, 129.1, 142.0, 145.7. IR (CDCl3) 1742 cm-1. EIMS
m/z 471 (3), 314 (7), 156 (15), 140 (100). E-20a : 1H NMR
(CDCl3) δ 0.66 (bs, 3), 0.96-1.82 (m, 33), 2.64-2.82 (m, 1),
2.94-3.08 (m, 1), 4.81 (dd, 1, J ) 5.1, 3.3 Hz), 5.70 (d, 1, J )
16.5 Hz), 6.76-6.88 (m, 1), 7.2-7.6 (m, 5). 13C NMR (CDCl3)
δ 16.5, 16.7, 20.1, 29.3, 31.4, 38.5, 39.2, 40.0, 59.6, 85.3, 121.7,
126.9, 127.0, 127.6, 142.0, 144.8. IR (CDCl3) 1731 cm-1. EIMS
m/z 471 (0.5), 314, 156 (30), 140 (100). E,Z-21a : 1H NMR
(CDCl3) δ 1.10 (s, 6), 1.19 (s, 6), 1.4-1.8 (m, 6), 5.79 (d, 1, J )
7.5 Hz), 6.76-6.86 (m, 2), 7.28-7.36 (m, 3), 7.46-7.56 (m, 2),
8.22 (dd, 1, J ) 10.1, 8.4 Hz). 13C NMR (CDCl3) δ 17.0, 20.6,
32.0, 39.1, 59.9, 115.6, 125.2, 127.4, 128.7, 128.9, 136.3, 141.1,
145.3. IR (CDCl3) 1735 cm-1. EIMS m/z 313, 157 (100).
HREIMS m/z calcd for C20H27NO2 313.2042, found 313.2043.
E,E-21a (mp 153-156 °C): 1H NMR (CDCl3) δ 1.09 (s, 6), 1.20
(s, 6), 1.4-1.8 (m,6), 6.04 (d, 1, J ) 11.7 Hz), 6.86-6.94 (m,
2), 7.3-7.6 (m, 6). 13C NMR (CDCl3) δ 17.0, 20.6, 31.9, 38.0,
60.1, 119.8, 126.0, 127.2, 126.2, 128.8, 129.0, 136.0, 140.4,
144.8. IR (CDCl3) 1728 cm-1. EIMS m/z 313 (0.1), 157 (100),
Gen er a tion of 2,2-Dim eth ylcyclop r op yl Keten e (14)
a n d Tr a p p in g w ith TMIO. 2,2-Dimethyl-1-cyclopropyl di-
azomethyl ketone (8e,16b 30 mg, 0.22 mmol) in 40 mL pentane
was irradiated for 4 min with 250 nm light and TMIO (104
mg, 0.55 mmol) was added at room temperature and the
solution stirred for 24 h. After evaporation of the pentane
chromatography (15% EtOAc /hexane) gave Z-24b (5 mg, 0.015
mmol, 7%) as a pale white solid (mp 87-90 °C) and E-24b (34
mg, 0.12 mmol, 53%) as a pale white solid (mp 75-77 °C).
Z-24b: 1H NMR (CDCl3) δ 1.41 (bs, 6), 1.49 (bs, 6), 1.88 (s, 3),
1.92 (s, 3), 5.8 (m, 1), 6.9-7.3 (m, 1), 7.08-7.16 (m, 4), 7.2-
7.3 (d, 1). 13C NMR (CDCl3) δ 18.5, 25.1, 25.7, 27.1, 29.2, 29.9,
68.4, 112.4, 121.8, 122.6, 127.8, 141.8, 144.5, 147.5, 167.6. IR
(CDCl3) 1739 cm-1. EIMS m/z 300 (1), 190 (19), 109 (100), 81
(29). HREIMS m/z calcd for C19H26NO2 300.1964, found
300.1972. E-24b: 1H NMR (CDCl3) δ 1.46 (bs, 6), 1.52 (bs,
6), 1.93 (s, 3), 1.95 (s, 3), 6.02-6.14 (m, 2), 7.12-7.2 (m, 2),
7.26-7.36 (m, 2), 7.73 (dd, 1, J ) 14.1, 11.4 Hz). 13C NMR
(CDCl3) δ 18.8, 25.2, 26.4, 28.6, 68.0, 115.8, 121.3, 123.7, 127.4,
142.1, 143.9, 146.8, 168.6. IR (CDCl3) 1732 cm-1. EIMS m/z
299 (0.5), 190 (5), 109 (100), 81 (35). HREIMS m/z calcd for
156. HREIMS m/z calcd for
C20H27NO2 313.2042, found
313.2047.
C
19H25NO2 299.1885, found 299.1882.
Gen er a tion of 2-P h en ylcyclop r op ylk eten e (13) a n d
Tr a p p in g w ith TMIO. E-2-Phenyl-1-cyclopropyl diazomethyl
ketone (8d ,16a 20 mg, 0.11 mmol) in 20 mL pentane was
irradiated for 7 min with 250 nm light and TMIO (51 mg, 0.27
mmol) was added and the solution stirred 20 h at room
Kin et ics of P h en ylk et en e (1a ) a n d TMIO. Ketene 1a
(0.020 mL of a 0.085 mM solution from 5 min irradiation of
diazoacetophenone with 300 and 350 nm light) was injected
into 1.2 mL of a 0.253 to 1.12 mM TMIO solution. The decrease
of the absorption at 249 nm gave good first-order kinetics.
Kin etics of n -Bu tylk eten e (1b) a n d TMIO. 1-Diazo-2-
hexanone (0.250 mL of a 0.0190 M solution in isooctane) was
(16) (a) Feldman, K. S.; Simpson, R. E. J . Am. Chem. Soc. 1989,
111, 4878-4886. (b) See Supporting Information.

Nitroxyl Radical Reactions
J . Org. Chem., Vol. 66, No. 17, 2001 5765
irradiated in a UV cell for 4 min at 250 nm to form 1b. This
was pipetted into a 1.2 mL UV cell containing 0.2-0.5 mL of
a 0.106 M TMIO solution. For the 0.2 mL TMIO solution 0.167
mL of diazoketone solution was used, and isooctane was added
to give final volumes of 0.75 mL. The decrease in the absorp-
tion at 355 nm gave good first-order kinetics.
IR Sp ectr a of Keten es. Cold solutions of the ketenes were
quickly transferred to an IR cell for observation of the ketene
bands.
Ack n ow led gm en t. Financial support by the Natu-
ral Sciences and Engineering Research Council of
Canada is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails and 1H NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O0102922