Photoinduced decarboxylation of 3-(N-phthalimido)adamantane-1-carboxylic acid and radical addition to electron deficient alkenes

Article abstract of DOI:10.1039/c0pp00357c

Direct and sensitized excitation of 3-(N-phthalimido)adamantane-1- carboxylic acid (1) leads to the population of the triplet state that, in the presence of a base, decarboxylates, giving N-(1-adamantyl)phthalimide (2) cleanly and efficiently (Φ = 0.11). The radical initially formed by decarboxylation adds regiospecifically to electron deficient alkenes, whereas radical addition was not observed for electron rich alkenes. The radical addition can also be applied to molecules not bearing adamantanes wherein the electron donor (carboxylate) and the acceptor (phthalimide) are separated by a rigid spacer. The photodecarboxylation induced radical addition of phthalimide derivative 1 to alkenes takes place in good to excellent yields and represents a mild and efficient method for C-C bond formation. The Royal Society of Chemistry and Owner Societies 2011.

Full text of DOI:10.1039/c0pp00357c

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PAPER
Photoinduced decarboxylation of 3-(N-phthalimido)adamantane-1-carboxylic
acid and radical addition to electron deficient alkenes†
Margareta Horvat,a Kata Mlinaric´-Majerski,a Axel G. Griesbeckb and Nikola Basaric´*a
Received 24th November 2010, Accepted 6th January 2011
DOI: 10.1039/c0pp00357c
Direct and sensitized excitation of 3-(N-phthalimido)adamantane-1-carboxylic acid (1) leads to the
population of the triplet state that, in the presence of a base, decarboxylates, giving
N-(1-adamantyl)phthalimide (2) cleanly and efficiently (U = 0.11). The radical initially formed by
decarboxylation adds regiospecifically to electron deficient alkenes, whereas radical addition was not
observed for electron rich alkenes. The radical addition can also be applied to molecules not bearing
adamantanes wherein the electron donor (carboxylate) and the acceptor (phthalimide) are separated by
a rigid spacer. The photodecarboxylation induced radical addition of phthalimide derivative 1 to
alkenes takes place in good to excellent yields and represents a mild and efficient method for C–C bond
formation.
and thioethers.11 Furthermore, intermolecular SET is involved in
photoinduced decarboxylations.12 Radicals that were formed on
Introduction
loss of CO2 reacted with phthalimide giving addition products.13
In addition, SET has been used in intramolecular reactions,
inducing cyclizations to medium and large rings.14 Particularly,
SET promoted desilylations were applied in the synthesis of
macrocyclic ethers,15 whereas decarboxylations have found use
in cyclizations of peptides.16 However, photodecarboxylation
induced addition to double bonds has not yet been reported
in phthalimide photochemistry, although it is known in the
photochemistry of carboxylic acids,17 where it has been initiated by
use of dicyanobenzenes as electron acceptors in the photoinduced
electron transfer processes.17
In continuation of our research on synthesis of unnatural
adamantyl amino acids,18 and their transformations to more
complex systems,19 we turned our attention to the photochemistry
of amino acids activated by a phthalimide moiety. Herein we report
on synthesis of 3-(N-phthalimido)adamantane-1-carboxylic acid
(1) and its photoinduced decarboxylation. Furthermore, for the
first time, we describe photodecarboxylative radical addition of
the phthalimide derivative to alkenes. The mechanism of the pho-
tochemical reaction was investigated by performing preparative
irradiations and laser flash photolysis. Since this hitherto unknown
photoinduced addition reaction of phthalimides represents a novel
mild method for C–C bond formation it may find application in
the functionalization of different molecules bearing phthalimide
as a photoactivation group.
Phthalimide is a versatile chromophore that has been exten-
sively used in different photochemical reactions with synthetic
applicability.1 Similar to simple carbonyl chromophores, excited
state phthalimide abstracts H-atoms from suitable H-donors
giving rise to addition and reduction products.2 Recently, we
reported the convenient photochemical formation of complex
benzazepinone derivatives by a domino photochemical reaction
of phthalimides that involves two consecutive intramolecular g-
H abstractions.3 The second type of photochemical reaction of
phthalimides is cycloaddition.4 Mazzocchi et al. reported a num-
ber of formal s + p cycloadditions that deliver benzazepinones.5
Finally, imide derivatives undergo photoinduced single electron
transfer (SET), and that probably represents the most widely used
photochemical reaction of phthalimides in organic synthesis.6
The reduction potential of ground state N-methylphthalimide
in DMF is -1.37 V vs. SCE (saturated calomel electrode).7
Taking into account the energy for the excitation to the sin-
2
2
glet and the triplet excited states (E00 = 3.8 eV and E00
=
3.1 eV, respectively), the reduction potentials in the excited states
are estimated to be 2.4 V, and 1.7 V vs. SCE, respectively.8
Consequently, phthalimides in the excited state are oxidants
that react with electron-rich substrates. Intermolecular SET has
been used in reactions of phthalimides with alkenes,9 amines,10
aDepartment of Organic Chemistry and Biochemistry, Ruąer Bosˇkovic´ Insti-
tute, Bijenicˇka cesta 54, 10000, Zagreb, Croatia. E-mail: nbasaric@irb.hr;
Fax: + 385 1 4680 195; Tel: +385 1 4561 141
bDepartment of Chemistry, University of Cologne, Greinstr. 4, Cologne, D-
50939, Germany
Results and discussion
† Electronic supplementary information (ESI) available: General and
detailed experimental procedure, physical characterization, 1H and 13C
NMR spectra of 1, 3a–3d, 5 and 7. See DOI: 10.1039/c0pp00357c
3-(N-Phthalimido)adamantane-1-carboxylic acid (1) was pre-
pared from 3-aminoadamantane-1-carboxylic acid20 and phthalic
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Table 1 Irradiation of 1 in the presence of alkenes and arenesa
would result from the intramolecular H-abstractions we have
previously reported.3 This is in accord with a much higher
quantum yield of the photodecarboxylative addition to alkenes
than that of the intramolecular H-abstraction, which is generally
low.
Entry
Alkene/Arene
2 (%)b
3 (%)b
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4f
4g
4h
4i
5
8
30
40
(3a) 95
(3b) 85
(3c) 60
(3d) 50
—
—
—
To get a deeper understanding of the mechanism of the
decarboxylation and the addition to alkenes, we carried out
irradiation of 1, with and without acrylonitrile, in acetone–
D2O, or D6-acetone–H2O, in the presence of K2CO3. Detection
of deuterated products in these experiments could indicate the
presence of carbanion or radical intermediates in the mechanism.
Irradiation of 1 in acetone–D2O furnished 2 without deuterium
being incorporated in the molecule (according to NMR and
MS), whereas irradiation in D6-acetone–H2O gave rise to 2 with
deuterium being incorporated at position 3 of the adamantane
skeleton (65% D according to MS). Irradiation of 1 in acetone–
D2O in the presence of 4a gave 3a with one deuterium almost
quantitatively incorporated (according to MS > 99% D) at the
position alpha to the CN group (see ESI†). Isolation of the
deuterated 2 indicates that the photodecarboxylation gives rise
to an adamantyl radical that abstracts an H-atom from acetone
giving 2. On the other hand, formation of deuterated 3a strongly
suggests intermediacy of a carbanion in its formation (vide infra,
Scheme 2).
To investigate the scope of the decarboxylative radical addition
to alkenes we performed the intermolecular version of the reaction,
that is, irradiation of admantane-1-carboxylic acid (5) and N-
methylphthalimide (6) in the presence of acrylonitrile (eqn (1)).
In accordance with previous findings, adamantane-1-carboxylic
acid underwent decarboxylation.12 However, no addition to the
alkene took place. Presumably, the reason for the lack of the
radical addition is slow intermolecular SET and decarboxylation,
as well as competitive polymerization of acrylonitrile. Thus,
whereas irradiation of 1 for 2 h gave complete conversion to
2 and 3, acid 5 and phthalimide 6 were irradiated for 18 h
to achieve complete conversion. During such a long irradia-
tion, acrylonitrile polymerized and only decarboxylation took
place without the addition products being observed by NMR
or GC.
20c
30c
80c
100c
100c
—
—
a Irradiation was carried out for 2 h in Ar-purged acetone–H2O in the
presence of K2CO3. b NMR ratio from the isolated mixture of products.
c Isolated yield.
anhydride. The reaction was carried out in anhydrous refluxing
DMF, yielding 1 in moderate yield (53%). Irradiation of 1
was performed under direct excitation and in the presence of
acetone or benzophenone sensitizers. Both direct and sensitized
excitation gave rise to decarboxylation, cleanly delivering N-
(1-adamantyl)phthalimide (2). The photodecarboxylation was
significantly more efficient in the presence of a protic solvent (H2O)
and base (K2CO3). The quantum yields of the photochemical
decarboxylation of 1 in basic CH3CN–H2O (3 : 1) and acetone–
H2O (3 : 1) was determined by use of photodecarboxylation of
4-(N-phthalimidomethyl)cyclohexane-1-carboxylic acid (8, eqn
(2)) as an actinometer (UR = 0.3).21 The quantum yields are
UR = 0.11 and UR = 0.50, respectively. The estimated values
for the quantum yield in the sensitized reaction (0.50), and on
direct excitation (0.11), are in good agreement with the quantum
yield of intersystem crossing (UISC = 0.22, vide infra). In order
to induce the addition of the adamantylphthalimide to double
bonds, or substitute the adamantyl moiety by an aryl group,
irradiations of 1 were carried out in the presence of alkenes and
arenes. Indeed, besides photodecarboxylation, for the first time
addition of phthalimide derivatives to double bonds was achieved.
Together with product 2, novel 1,3-disubstituted adamantane
derivatives 3 were obtained in good yields (Scheme 1). However,
products 3 were obtained only with electron deficient alkenes. In
the presence of electron rich alkenes or arenes, irradiation gave
high-molecular weight products, or only decarboxlyation took
place yielding 2 (Table 1). Irradiations were generally performed
until the complete conversion of 1 was achieved. However, we
have not observed formation of secondary photoproducts that
(1)
Thescopeofthereactionwasalsoinvestigatedforthederivatives
without the adamantane skeleton. We performed irradiation of
trans-4-(N-phthalimidomethyl)cyclohexane-1-carboxylic acid (8,
used as an actinometer, vide supra) in the presence of acrylonitrile.
However, under the irradiation conditions where 1 gave 95%
yield of 3a, intramolecular cyclization and decarboxylation of 8
took place and no intermolecular addition product was isolated
(eqn (2)).
Scheme 1
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Scheme 2
The successful decarboxylative addition was achieved with the
N-phenylphthalimide derivative 11.22 Irradiation of 11 in the
presence of acrylonitrile gave decarboxylation product 1223 and
addition product 13 (eqn (3)). This finding indicates that the
decarboxylative addition principally can be used as a method for
C–C bond formation in the synthesis of different compounds.
However, the electron donor and the acceptor in the SET reaction
have to be separated by a rigid spacer to prevent the cyclization.
Since photodecarboxylation of 1 takes place with sensitized or
direct excitation, it is reasonable to assume that it is a triplet
excited state process. However, the decarboxylation reaction is not
quenched by O2, suggesting that it is not a reaction taking place
from the T1 state. To get more insight into the photochemical
reaction mechanism and characterize the triplet excited state
we carried out laser flash photolysis (LFP). The LFP of the
CH3CN solution of 1 gave rise to transient absorption with the
maximum at 340 nm (Fig. 1a) decaying with the rate constant
k = 7.7 ¥ 104 s-1 (t = 13 ms). Comparison with the reported
similar transient absorptions of the phthalimide chromophore24
indicated the transient can be assigned to the T1 state of 1.
The quantum yield of the intersystem crossing was estimated
from the comparison of the intensity of the transient absorption
with the optically matched solution of N-methylphthalimide
(2)
(3)
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Fig. 1 Transient absorption spectra of 1 in N2-purged CH3CN (left), and N2-purged CH3CN–H2O (1 : 1) in the presence of K2CO3 (right). Inset: decay
at 340 nm in CH3CN.
(UISC = 0.8), UISC = 0.22.24c LFP experiments were also carried out
under benzophenone sensitization (excitation 355 nm). We found
that 1 quenches the triplet state of benzophenone. However, due
to the overlapping of the transient absorption signals, quantitative
analysis was difficult. The transient assigned to the phthalimide
triplet (T1) can be quenched by O2 and ethyl vinyl ether (EVE)
with the quenching rate constants kq = 2 ¥ 109 M-1 s-1 and kq =
3 ¥ 109 M-1 s-1, respectively. In CH3CN–H2O solution in the
presence of a base, more persistent transients were observed with a
maximum at 400 nm. The latter were assigned to the phthalimide
radical anion that is formed via intramolecular SET from the
deprotonated carboxyl group (donor) to the phthalimide in the
triplet excited state.
From the above findings, a mechanism for the photochemical
reaction of 1 can be proposed (Scheme 2). On excitation (direct
or sensitized) the T1 state of the phthalimide, detectable by LFP,
is populated. However, the T1 is probably not the reactive state
that delivers products, as suggested from the inability of oxygen
to quench the decarboxylation reaction. Probably, the reaction
takes place from an upper excited triplet state, in accordance with
previous findings.3b,24c,d However, singlet excited state reactivity
cannot be excluded. In the basic solution the upper triplet state
of 1 undergoes intramolecular SET and gives biradical anion
BRA1 that rapidly and irreversibly decarboxylates, giving BRA2.
Probably, the phthalimide radical anion detected by LFP (Fig. 1b)
corresponds to BRA2, and is characterized by a relatively long
lifetime. BRA2 reacts as a radical with alkenes giving BRA3,
or becomes protonated by H2O to give BR1. Although the
pKa value of the phthalimide radical anion is not known, its
protonation and formation of the ketyl radical species in protic
solvents has been reported.25 The reaction of BRA2 with H2O,
followed by an H-atom transfer from acetone, ultimately delivers
the decarboxylation product 2, particularly in the absence of
alkenes. The isolation of deuterated 2 on irradiation in D6-acetone
and finding that 2 without deuterium is formed on irradiation
in D2O shows that H-transfer from acetone delivers 2, and not
the intermolecular H-transfer from the OH(D) ketyl radical.
BRA3 formed in the reaction with electron deficient alkenes (R =
CN, COOCH3) most probably undergoes back electron transfer
to deliver stabilized anion 3a- and regenerate the phthalimide
moiety. The protonation of anion 3a- by H2O yields the isolated
addition products 3a. Although, to the best of our knowledge,
such a mechanism of photochemical reaction of phthalimides
involving back electron transfer is not known, formation of
the deuterated 3a on irradiation in D2O strongly indicates the
intermediacy of the anion 3a-. In addition, back electron transfer
after addition is the ubiquitous process in photo-NOCAS26 and
photo-ROCAS reactions.27 The other less likely option for BRA3
may be protonation of the radical anion moiety to BR2, followed
by an intra- or an intermolecular H (D)-transfer yielding 3a. In
principle, formation of products 3 can also take place via a radical
addition of alkene to BR1 giving BR2, or a back electron transfer
on BR1 giving zwitterion ZW1 that would react with alkene in
a mechanism of Michael addition. However, since we have not
detected deuterium in phthalimide 2, the latter mechanism of back
electron transfer prior to the addition to the double bond can be
disregarded. Probably, the presence of the electron withdrawing
group is essential for the back electron transfer.
Radical addition of BRA2 to double bonds was only observed
with electron deficient alkenes. The absence of the addition
reaction with electron rich alkenes (entry 5 and 6, Table 1) is
in accordance with the nucleophilic character of the adamantyl
radical.28 In addition, the lack of the addition reaction can be
explained by quenching of the triplet state of 1 by these alkenes via
intermolecular electron transfer. The T1 state is quenched by EVE
(vide supra). However, the Stern–Volmer quenching (see ESI†) is
not indicative if EVE interacts with the upper triplet excited states.
Quenching of the phthalimide excited state by electron rich alkenes
via electron transfer, ultimately leading to the cycloaddition
products, has been reported, wherein the triplet excited state
reactivity has been precluded.29 Consequently, in the presence of
electron rich alkenes decarboxylation probably does not take place
and the radical-cation of the alkene ultimately initiates formation
of high-molecular weight material. Furthermore, if BRA3 was
formed by an addition to an alkene bearing an electron donating
group, back electron transfer giving 3- would not take place. The
BRA3 would then probably undergo cleavage to yield 2, or initiate
polymerization of the alkene.
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Although adamantyl radicals have nucleophilic character,
BRA2 reacts with allyl bromide as a typical radical resulting in
abstraction of a Br-atom and formation of a stable allyl radical
that eventually forms polymers (eqn (4)). Such a reaction wherein
the adamantyl radical abstracts bromine from the allyl bromide
has been reported.30 We cannot rule out, however, that BRA2
adds to the double bond of the allyl bromide and gives a Br-
radical. The latter reaction would give an adamantylalkene that
is probably unstable and easily undergoes polymerization under
irradiation conditions. The inability of arenes to react with 1 to
give arylation products (entry 7–9, Table 1) may be explained by
quenching of the triplet state of 1 by energy transfer to arenes. The
other plausible reason may be too low radical-like reactivity of the
adamantyl radical BRA2 with arenes, and/or too high energy for
the C–X bond cleavage.
MeOH–CH2Cl2 as eluent. Pure photochemical products 3a–3d
were obtained by preparative TLC using CH2Cl2–Et2O (9 : 1), or
CH2Cl2–EtOAC–CH3OH (8.5 : 1 : 0.5).
3-(N-Phthalimido)-1-(2-cyanoethyl)adamantane (3a). 92 mg
(89%); yellowish oil; IR (KBr) nmax/cm-1 3457.6, 2911.5, 2852.9,
2245.4, 1769.1, 1706, 1368.8, 1314.4, 1078.6, 718.8; 1H NMR
(CDCl3, 600 MHz) d (ppm) 7.76–7.73 (m, 2H), 7.69–7.66 (m, 2H),
2.47 (d, 2H, J = 11.7 Hz), 2.44 (d, 2H, J = 11.7 Hz) 2.35–2.31 (m,
2H), 2.27–2.25 (m, 2H), 2.24 (s, 2H), 1.79–1.74 (m, 1H), 1.63–1.58
(m, 3H), 1.56 (dd, 2H, J = 1.2 Hz, J = 12.2 Hz), 1.49 (dd, 2H, J =
1.2 Hz, J = 12.2 Hz); 13C NMR (CDCl3, 75 MHz) d (ppm) 169.5
(s, 2C, C O), 133.6 (d, 1C), 131.7 (s, 2C), 122.4 (d, 2C), 120.3 (s,
1C, CN), 60.3 (s, 1C), 43.8 (t, 1C), 40.1 (t, 2C), 39.2 (t, 2C), 38.6
(t, 1C), 35.2 (t, 1C), 34.3 (s, 1C), 29.4 (d, 2C), 11.0 (t, 1C); HRMS,
calcd for C21H22N2O2+H+ 335.1749; obsd 335.1749.
3-(N-Phthalimido)-1-(3-methoxy-3-oxopropyl)adamantane (3b).
1
40 mg (33%); light yellow oil; H NMR (CDCl3, 600 MHz) d
(ppm) 7.75–7.74 (m, 2H), 7.67–7.66 (m, 2H), 3.67 (s, 3H, OCH3),
2.46–2.44 (m, 4H), 2.33–2.30 (m, 2H), 2.23 (br s, 4H), 1.73 (d, 1H,
J = 12.4 Hz), 1.59 (d, 1H, J = 12.4 Hz), 1.56–1.53 (m, 4H), 1.45 (d,
2H, J = 12.2 Hz); 13C NMR (CDCl3, 150 MHz) d (ppm) 174.6 (s),
169.6 (s, 2C), 133.5 (d, 2C), 131.8 (s, 2C), 122.4 (d, 2C), 60.7 (s),
51.4 (q), 44.2 (t), 40.4 (t, 2C), 39.5 (t, 2C), 38.1 (t), 35.4 (t), 34.2 (s),
29.6 (d, 2C), 27.8 (t); IR (KBr) nmax/cm-1 3452.2, 2913.3, 1718.3,
1447.5, 1356.3, 1312.1, 1172.3, 1076.1, 718.7; HRMS, calcd for
C22H25NO4+Na+ 390.1676; obsd 390.1676.
(4)
Conclusion
After direct or sensitized excitation of phthalimide 1, the triplet
state is populated, and in the presence of a base undergoes
decarboxylation (U = 0.11). The adamantyl radical formed by
decarboxylation reacts with electron deficient alkenes giving
addition products. The hitherto unreported addition reactions
represent mild and efficient route to C–C bond formation. Since
functionalization of the alkene allows for further derivatizations,
this reaction could be applied in the synthesis of more complex
adamantane derivatives and cage molecular structures, bearing
phthalimide as a photoactivating group. In addition, the decar-
boxylative addition can be applied in the synthesis of molecules
not bearing adamantanes providing that the phthalimide and the
carboxylic acid are separated by a rigid spacer.
3-(N-Phthalimido)-1-(3-oxocyclohexyl)adamantane
(3c).
36 mg (29%); colorless oil, 1H NMR (CDCl3, 300 MHz) d
(ppm) 7.77–7.72 (m, 2H), 7.70–7.65 (m, 2H), 2.52–2.44 (m,
5H), 2.43–2.36 (m, 1H), 2.36–2.32 (m, 1H), 2.31–2.17 (m, 4H),
2.16–2.05 (m, 2H), 2.00 (d, 1H, J = 12.7 Hz), 1.76 (d, 1H, J = 12.5
Hz), 1.64–1.56 (m, 3H), 1.53–1.30 (m, 5H); 13C NMR (CDCl3,
75 MHz) d (ppm) 212.6 (s), 169.6 (s, 2C), 133.6 (d, 2C), 131.7 (s,
2C), 122.4 (d, 2C), 61.0 (s), 49.0, (d), 42.0 (t), 41.8 (t), 41.3 (t),
39.7 (t), 39.6 (t), 38.3 (t), 37.6 (t), 36.9 (s), 35.6 (t), 29.6 (d), 29.6
(d), 25.4 (t), 24.6 (t); IR (KBr) nmax/cm-1 2909.8, 2854.7, 1769.3,
1702.1, 1466.9, 1450.9, 1702.1, 1364.6, 1313.7, 1076.4; HRMS,
calcd for C24H27NO3+Na+ 400.1883; obsd 400.1866.
Experimental
Irradiation of 3-(N-phthalimido)adamantane-1-carboxylic acid (1)
3-(N-Phthalimido)-1-bromadamantane (3d). 10 mg (9%); col-
orless oil; 1H NMR (CDCl3, 300 MHz) d (ppm) 7.80–7.73 (m, 2H),
7.71–7.64 (m, 2H), 2.51 (br s, 2H), 2.48–2.33 (m, 6H), 1.83–1.65
(m, 5H), 1.56 (ddd, 1H, J = 8.0 Hz, J = 10.7 Hz, J = 12.6 Hz);
13C NMR (CDCl3, 150 MHz) d (ppm) 169.4 (s, 2C), 133.7 (d, 2C),
131.7 (s, 2C), 122.6 (d, 2C), 69.2 (s), 68.2 (s), 47.8 (t), 43.8 (t, 2C),
38.8 (t, 2C), 34.6 (t), 30.7 (d, 2C); IR (KBr) nmax/cm-1 3447.4,
2915.1, 2855.6, 1769, 1704.3, 1354.8, 1308.7, 1121.3, 1100.2,
1077.5, 719.27; HRMS, calcd for C18H18BrNO2+H+ 360.0594;
obsd 360.0594.
in the presence of alkenes and arenes, general procedure
A solution of 3-(N-phthalimido)adamantane carboxylic acid (1)
(100 mg, 0.307 mmol), K2CO3 (21 mg, 0.1535 mmol) and alkene
or arene 4 (3.070 mmol) in 200 mL acetone–H2O (3 : 1) was
irradiated at 300 nm in a Rayonet reactor (8 lamps) over 2 h and
continuously purged with argon and cooled with an internal cold
finger condenser (tap water). After irradiation, most of the acetone
was removed on a rotary evaporator and the residue extracted with
CH2Cl2 (3 ¥ 50 mL). After the extraction, the aqueous phase was
acidified to pH 3 by addition of HCl (0.1 M), and extraction with
EtOAc was carried out (3 ¥ 50 mL). The organic extracts were
dried over anhydrous MgSO4. After filtration and evaporation
of the solvent photochemical products were obtained from the
CH2Cl2 solution, whereas unreacted 1 was recovered from EtOAc.
The ratio of the photoproducts 2 and 3 was determined by NMR.
Alternatively, after irradiation, the solvent (acetone and H2O)
was removed on a rotary evaporator and the residue chro-
matographed on a column filled with silica gel using 0–10%
3-(N-Phthalimido)-1-(2-cyano-2-deuterioethyl)adamantane (3a-D)
A solution of 3-(N-phthalimido)adamantane carboxylic acid
(1) (10 mg, 0.031 mmol), K2CO3 (2.1 mg, 0.015 mmol) and
acrylonitrile 4a (20 mL, 0.31 mmol) in 20 mL acetone–D2O (3 : 1)
was irradiated at 300 nm in a Rayonet reactor (8 lamps) for 45 h
and continuously purged with argon and cooled with an internal
cold finger condenser (tap water). After irradiation, the solvent
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was removed on a rotary evaporator and the residue dissolved in
CDCl3 to record its NMR spectra. Yellowish oil, 1H NMR (CDCl3,
600 MHz) d (ppm) 7.76–7.73 (m, 2H), 7.69–7.66 (m, 2H), 2.47 (d,
2H, J = 11.7 Hz), 2.44 (d, 2H, J = 11.7 Hz) 2.33–2.29 (m, 1H),
2.27–2.25 (m, 2H), 2.24 (s, 2H), 1.80–1.76 (m, 1H), 1.61–1.59 (m,
3H), 1.56 (dd, 2H, J = 1.2, J = 12.2 Hz), 1.49 (dd, 2H, J = 1.2 Hz,
J = 12.2 Hz); 13C NMR (CDCl3, 150 MHz) d (ppm) 169.6 (s, 2C),
133.6 (d, 2C), 131.8 (s, 2C), 122.3 (d, 2C), 120.3 (s), 60.4 (s), 43.9
(t), 40.2 (t, 2C), 39.4 (t, 2C), 38.6 (t), 35.3 (t), 34.4 (s), 29.5 (d, 2C),
10.8 (dt, JHD = 20.1 Hz); MS (ESI, m/z), 337 (25, M+H+), 336
(100, M+H+).
Acknowledgements
These materials are based on work financed by the Ministry of
Science Education and Sports of the Republic of Croatia (grant
No. 098-0982933-2911), National Foundation for Science, Higher
Education and Technological Development of the Republic of
Croatia (NZZ grant no. 02.05/25) and the Deutsche Forschungs-
gemeinschaft. The support of DAAD and The Croatian Ministry
of Science, Education and Sports on the bilateral project is also
gratefully acknowledged. We thank Professors Peter Wan and
Cornelia Bohne, and the University of Victoria (Victoria, Canada,
BC) for the use of nanosecond LFP.
N-(3-Deuteroadamantyl)phthalimide (D–2)
A solution of 3-(N-phthalimido)adamantane carboxylic acid (1,
10 mg, 0.031 mmol) and K2CO3 (2.1 mg, 0.015 mmol) in 3 mL
d6-acetone–H2O (3 : 1) was divided in three quartz NMR tubes.
Each solution was purged with argon and irradiated at the same
time in a Rayonet reactor (8 lamps) for 7 min at 300 nm. After
irradiation, samples were combined and solvent was removed on a
rotary evaporator. Pure product was isolated on preparative TLC
with 5% MeOH–CH2Cl2 as eleunt and characterized by NMR and
MS spectra.
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5 mg, colorless crystals, 1H NMR (CDCl3, 300 MHz) d (ppm)
7.78–7.71 (m, 2H), 7.69–7.62 (m, 2H), 2.51 (s, 6H), 2.16 (s, 2H)
1.84–1.66 (m, 6H); MS (ESI, m/z), 283.2 (100, M+H), 284.2 (21).
Irradiation of 4-(N-phthalimido)phenyl acetic acid (11) in the
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max/cm-1 2933, 2856, 2244, 1717, 1516, 1395, 1121, 1099, 1083,
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All LFP studies were conducted at the University of Victoria
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