Radical carbodiazenylation - A convenient and effective method to achieve carboamination of non-activated olefins

Article abstract of DOI:10.1002/ejoc.200800250

The regioselective addition of aryl and aryldiazenyl substituents to olefinic substrates can be described as carbodiazenylation. In this report we present our final results relating to this unique type of radical functionalization reaction, which has now

Full text of DOI:10.1002/ejoc.200800250

FULL PAPER
DOI: 10.1002/ejoc.200800250
Radical Carbodiazenylation – A Convenient and Effective Method to Achieve
Carboamination of Non-Activated Olefins
Olga Blank,[a] Alexander Wetzel,[a] Daniela Ullrich,[a] and Markus R. Heinrich*[a]
Keywords: Radical reactions / Olefins / Arenediazonium salts / Carboamination
The regioselective addition of aryl and aryldiazenyl substitu-
ents to olefinic substrates can be described as carbodiazenyl-
ation. In this report we present our final results relating to
this unique type of radical functionalization reaction, which
has now been developed into a convenient, versatile and
highly effective synthetic method. Starting from an investiga-
tion into rate constants for the addition of aryl radicals to
monosubstituted, non-activated olefins, this key step is
shown to be both fast and selective in mixtures of dimethyl
ation is the formation of biaryl azo compounds. A careful
adjustment of the carbodiazenylation procedure led to
significantly improved results and now permits the synthesis
of previously inaccessible products. New applications of car-
bodiazenylation such as the synthesis of 1,2-diazabutadi-
enes, tetrahydropyridazines and substituted tricyclanes were
investigated. Apart from this, we describe a convenient two-
step sequence for intermolecular carboamination.
sulfoxide and water. The by-products obtained in earlier re- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
actions reveal that the main complication of carbodiazenyl-
Germany, 2008)
of carbodiazenylation were reported by Levisalles and
Rudler[14] in relation to mechanistic studies of the Meerwein
arylation.[15] A few reactions with activated olefins were
later published by Citterio and Minisci.[16] All of these early
carbodiazenylation reactions were already taking advantage
of the fact that arenediazonium salts can act as a source
of aryl radicals,[17] or as radical scavengers when reductive
conditions are applied. In this way, β-arylazo compounds
can be obtained in a simple one-step procedure from readily
available olefins and diazonium salts (Scheme 1). The azo
compounds accessible by carbodiazenylation are of particu-
lar interest since suitable further reductive treatment leads
to biologically active β-arylamines and recovery of one ani-
line equivalent, which can be reused for the synthesis of the
diazonium salt.
Introduction
Several synthetic efforts to achieve carboamination of
non-activated olefins have been reported in the last few
years. Among the organometallic methods, olefinic amines
have been cyclized to give pyrrolidines,[1] isoxazolidines,[2]
piperidines[3] and piperazines[4] through palladium catalysis.
2-Alkynyl-substituted anilines[5] and isocyanates[6] have
served as precursors for indoles in the presence of transition
metals, and imines have been induced to react with alkynes
in the presence of zirconium[7] and titanium[8] catalysts. All
these approaches have in common the fact that two of three
basic components – carbon equivalent, olefin and amine
equivalent – are linked, so that the overall reaction is par-
tially intramolecular.[9] Radical chemistry, in contrast, is not
limited in this way, and less complex starting materials can
be used. In a three component mixture, carbon-centred rad-
icals add to olefins, and the resulting adduct radicals are
subsequently trapped by a nitrogen-centred scavenger. The
best studied radical reaction of this type is carboazid-
ation.[10] In this case, sulfonyl azides are employed as nitro-
gen equivalents, and carboamination products can be ob-
tained from the alkyl azides by simple reductive workup.[11]
Our approaches to achieve carboamination are based on
the capability of arenediazonium salts to act as highly ef-
ficient scavengers for nucleophilic, carbon-centred radi-
cals.[12,13] In analogy to carboazidation, the overall reaction
can be described as carbodiazenylation. The first examples
Scheme 1. Carboamination of olefins by a carbodiazenylation/re-
duction sequence.
Although this strategy for olefin functionalization ap-
pears both simple and powerful, for a long time it was not
developed into a bona fide synthetic method. This is proba-
bly due to the fact that non-activated olefins, which repre-
[a] Organische Chemie 1, Technische Universität München
Lichtenbergstraße 4, 85747 Garching, Germany
Fax: +49-89-289-13329
E-mail: Markus.Heinrich@ch.tum.de
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O. Blank, A. Wetzel, D. Ullrich, M. R. Heinrich
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sent the largest group of potential substrates, were believed derived in earlier experiments conducted in tetrachlorocar-
to possess insufficient reactivity for aryl radical additions. bon.[17] Bearing in mind this significant dependence of aryl
These circumstances are reflected to some degree in the radical reactivity on the solvent, we became interested in
wide range of rate constants that have been published for which way our optimized mixture of dimethyl sulfoxide and
addition steps of aryl radicals to non-activated olefins.[18] water would affect aryl radical additions to olefins. We
Synthetic applications of aryl radicals involving olefinic therefore set up a competition experiment in which we com-
substrates therefore remained practically limited to the well pared the reactive, electron-deficient olefin ethyl acrylate
known Meerwein reactions in which activated (vinylic, do- with the non-activated olefin allyl acetate. Rate constants
nor- or acceptor-substituted) alkenes are commonly for aryl radical additions to various α,β-unsaturated car-
used.[19] Successful, high-yielding additions to non-acti- bonyls are known in the literature,[12b] since these types of
vated olefins were almost exclusively observed in intramo- alkenes have served numerous times as reactants in Meer-
lecular cyclization reactions.[20–22] Remarkable exceptions wein arylations. For the trapping of the radical adduct and
are Raucher’s indole synthesis, employing vinyl bromide,[23] to prevent oligomerization, we added tetramethylpiperdine-
Gorbovoi’s chloroarylation of allylic alcohols[24] and the al- 1-oxyl (TEMPO) to the reaction mixture.[28] The results ob-
lylation reactions with allyl bromide reported by Frejd.[25]
tained in three different experiments are summarized in
Scheme 2. In the first attempts, we generated aryl radicals
from the diazonum salts 1a and 1b in a mixture of dimethyl
sulfoxide and water (5:1). The third experiment was con-
ducted in dichloromethane, and carbodiazone 2 was used
Results and Discussion
Starting from our initial results on carbodiazenyla- as precursor for the aryl radicals in a photochemical reac-
tion[26a] of non-activated olefins, we turned our attention tion.[29] In all cases, ten equivalents of each olefin 3a and
and efforts towards the development of reaction conditions 3b were added to maintain nearly constant olefin concen-
that would allow the functionalization of a broad range of trations throughout the course of the reaction.
olefinic substrates with a large variety of diazonium salts.
Since the presence of water appeared to be a key element
for successful carbodiazenylations, we tried to find a suit-
able co-solvent to achieve sufficient solubilities for lipo-
philic alkenes. In this case, we were happy to see that a
decrease in the water content in dimethyl sulfoxide down to
two percent still gave satisfactory results.[26b] This particular
mixture now allowed the conversion of lipophilic olefins
such as oct-1-ene and was luckily not troubled by side-reac-
tions involving the solvent. As our first carbodiazenylation
procedure, which had employed titanium(III) chloride as re-
ductant, was also limited in the sense that only acceptor-
substituted arenediazonium salts were reduced in reason-
able reaction times,[26a,26c,26d] we changed to iron(II) sulfate
as reducing agent.[26b] With respect to the pH-dependent
reduction potential of iron(II) ions, the quasi-neutral mix-
tures of dimethyl sulfoxide and water described above
turned out to be perfect solvents, since the reductive power
Scheme 2. Determination of relative rate constants for the addition
of iron(II) rapidly decreases under acidic conditions. Even
of aryl radicals to the activated olefin ethyl acrylate (3a, kactiv) and
the non-activated olefin allyl acetate (3b, knonactiv).
weak acids such as acetic acid no longer allow the iron(II)-
mediated reduction of donor-substituted (e.g., 4-methoxy)
arenediazonium salts at room temperature.[27]
The fact that synthetically useful yields (50 to 65%) of
The relative addition rates of the aryl radicals to ethyl
carbodiazenylation products can be obtained with a rela- acrylate (3a) and to allyl acetate (3b) can be calculated from
tively low excess of olefin (3 to 5 equiv.) shows that the aryl the ratios of the products 5a/5b and 5c/5d, which were de-
radical addition to the non-activated olefin, which is the termined by proton NMR analysis of the crude reaction
crucial key step of the reaction, has to be efficient. The mixtures. Firstly, the observation that all three reactions
fastest rate constants ever reported for this type of radical give similar product ratios is one more piece of evidence
reaction were determined by Ingold and Lusztyk in water for the aryl radical as common intermediate. Secondly, the
as sole solvent.[18a] Aryl radicals generated from sodium 4- experiments show that aryl radical addition to non-acti-
iodophenylsulfonate by laser flash photolysis reacted with vated olefins is only eight times slower (averaged from the
non-activated olefins at rates of k ≈ 2–3ϫ107 –1 s–1, and three experiments) than that to activated acrylates. From
the authors pointed out that the fast and selective aryl radi- the known literature[12b] rate of addition to an activated
cal addition was largely due to the aqueous solvent. For substrate (kactiv ≈ 2ϫ108 –1 s–1, determined for vinyl
comparison, rate constants as low as k ≈ 5ϫ105 –1 s–1 were methyl ketone) one can estimate a rate constant of knonactiv
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Carboamination of Non-Activated Olefins
Х 7.3ϫ107 –1 s–1, which is in good agreement with the
value found by Ingold and Lusztyk.[18a] Although the sig-
nificant change in the nature of the solvent, from aqueous
dimethyl sulfoxide to dichloromethane in the photochemi-
cal experiments, does not remarkably affect the product ra-
tio, there is a significant difference in the overall outcome
in the two reaction types. Combined yields of up to 75% (5a
and 5b) were obtained from the iron(II)-mediated process,
whereas the photochemical reaction furnished products 5a
and 5b in only 40% total yield. These results can be ex-
plained by the reduced reactivity of the TEMPO radical in
polar solvents.[30] Aryl radical trapping by TEMPO there-
fore occurs to a decreased extent in aqueous dimethyl sulf-
oxide, which in turn raises the effectiveness of olefin ad-
dition. We recently used this finding for the development of
a novel intermolecular carbohydroxylation process.[31]
In contrast with the rather slow recombination with
TEMPO in polar solvents, aryl radicals readily abstract io-
dine atoms from alkyl iodides at practically diffusion-con-
trolled rates (kIT ≈ 109 –1 s–1).[32] The result of a second
competition experiment comparing aryl radical reactivity
towards 2-iodopropane (6) and allyl acetate (3b) by exami-
nation of the product ratio of 4-iodoanisole (7) and olefin
adduct 5d at low conversions led to a ratio of the rate con-
stants kIT/knonactiv = 46:1 (Scheme 3). From this result and
from the value of kIT discussed above, a rate constant of
knonactiv ≈ 2ϫ107 –1 s–1 (comparable to the one determined
before; see Scheme 2) can be derived.[33]
Scheme 4. Key steps of the carbodiazenylation process.
a carbodiazenylation reaction. Indeed, biaryl azo com-
pounds were found in significant amounts in the reactions
conducted according to the procedures developed so far.
The only practicable solution to circumvent this undesired
side-reaction would be to reduce the concentration of the
diazonium salt in the reaction mixture. On the other hand,
this modification could negatively affect the trapping of the
alkyl radicals by the arenediazonium salts in the second
stage of the desired radical pathway (Scheme 4, Path A).
To find out in which way lower concentrations of the
diazonium ions would influence the overall outcome, we
carried out a number of experiments in which we added
the salts slowly to the reaction mixture. In the first set of
experiments, we examined the behaviour of the 1,1-disubsti-
tuted olefins β-methallyl alcohol (3c) and β-methallyl ace-
tate (3d). To obtain an insight into the influence of the sub-
stitution pattern on the aromatic ring of the diazonium
salts, we included the donor-substituted para-methoxy salt
1b, the more or less neutral para-fluoro salt 1c and the more
reactive acceptor-substituted ortho-methoxycarbonyl diazo-
nium salt 1d in our study. The results are summarized in
Table 1. Comparison with earlier experiments (Table 1, En-
Table 1. Carbodiazenylation of 1,1-disubstituted olefins 3c and 3d.
Scheme 3. Determination of relative rate constants for iodine trans-
fer (kIT) to the aryl radical and addition to the non-activated olefin
allyl acetate (knonactivЈ).
Olefin 3
Arenediazonium salt 1 % Yield[a] % Yield[b]
R1
R2
8
8
Literature data,[12b,12c] combined with the rate constants
determined for the aryl radical addition to non-activated
olefins (k ≈ 7.3ϫ107 –1 s–1, see Scheme 2 and Scheme 3),
lead to an overview over the main steps occurring in a car-
bodiazenylation reaction (Scheme 4).
1
2
3
4
5
6
OH (3c)
OH (3c)
OH (3c)
OAc (3d)
OAc (3d)
OAc (3d)
p-OMe (1b)
p-F (1c)
77 (8a)
66 (8b)
70 (8c)
78 (8d)
91 (8e)
83 (8f)
63 (8a)
–
o-CO2Me (1d)
p-OMe (1b)
p-F (1c)
–
60 (8d)
–
–
o-CO2Me (1d)
From a comparison of the rate constants knonactiv and
kdiazo it is obvious that azo coupling to biaryl azo com-
[a] Yields by improved procedure. [b] Yields obtained from earlier
pounds (Scheme 4, Path B) remains a competing process in procedures; see ref.[26b]
.
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O. Blank, A. Wetzel, D. Ullrich, M. R. Heinrich
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tries 1 and 4) shows that the modified procedure is superior in a way to give more than 65% yields of the carbodiazenyl-
to the previous protocol, in which the diazonium salt was ation products reliably with any type of diazonium salt and
added all at once at the beginning. Only traces of biaryl azo monosubstituted, non-activated olefin. The maximum
compounds were found in the crude product mixture, which yields achieved by variation of the rate of addition are re-
indicated that the slow addition of the diazonium salt had ported in order to demonstrate the potential of the reaction.
indeed had the desired effect. Apparently, the highly effec- In our optimization attempts, we also found that the diazo-
tive alkyl radical trapping (k ≈ 1ϫ108 –1 s–1) in the second nium salt can be added either as a solid in small portions or
stage of the carbodiazenylation reaction does not suffer as dropwise in solution without significant negative or positive
a result of the lowered concentrations of diazonium salt effects.
(Scheme 4, Path A). Among the three different diazonium
salts 1b–1d no specific trends became apparent. As far as
Table 2. Carbodiazenylation of monosubstituted olefins 3b, 3e and
3f.
the olefins are concerned, β-methallyl acetate (3d, En-
tries 4–6) gave slightly better yields, which is most probably
due to decreased hydrogen abstraction from the olefin (see
also Figure 1).
Olefin 3
Arenediazonium salt 1 Maximum % Yield[b]
% yield[a]
R1
R2
8
8
1
2
3
4
5
6
7
OAc (3b)
OAc (3b)
OAc (3b)
OH (3e)
OH (3e)
OH (3e)
p-OMe (1b)
p-F (1c)
80 (8 g)
81 (8h)
78 (8i)
58 (8 g)
–
o-CO2Me (1d)
p-OMe (1b)
p-F (1c)
64 (8 g)
83 (8j)
–
–
–
Figure 1. Degree of hydrogen abstraction from olefinic substrates
3b–e and 3g–j given in percentages of total yields based on aryl
radical precursors.
80 (8k)
65[c] (8l)
76 (8m)
o-CO2Me (1d)
CH2OH (3f) p-OMe (1b)
56 (8 g)
[a] Yields by improved procedure. [b] Yields obtained from earlier
procedures; see ref.[26b]. [c] Product 8l easily undergoes isomeriza-
tion to the corresponding hydrazone.
Since the effectiveness of alkyl radical trapping by diazo-
nium salts is known to depend on the nucleophilicity of the
alkyl radical (Scheme 1, Path A, R1 = H),[12b] we expected
difficulties in reactions that pass through less nucleophilic
secondary rather than tertiary alkyl radicals. For this sec-
ond series of experiments (Table 2), we used allyl acetate
(3b), allyl alcohol (3e) and but-3-en-1-ol (3f) as substrates.
Given this less favourable background, we were surprised
to obtain better results than in the previous procedure. In
addition to increased yields, further advantages of the slow
diazonium salt addition turned out to be the cleanness and
the mildness of the reaction. Most products were obtained
in purities that could not be further improved by column
chromatography. The content of biaryl azo compounds was
again reduced to trace amounts. Carbodiazenylation prod-
ucts of allyl alcohol (Entries 4–6), which easily undergo
isomerization to the corresponding hydrazones and subse-
quent hydrolysis to the hydroxyketones, could not be ob-
tained by earlier procedures. In all of the second set of reac-
tions (Table 2), the rate of addition of diazonium salt to
the reaction mixture turned out to be the critical element.
As well as biaryl azo coupling, which can successfully be
suppressed by the protocol described above, another unde-
sired side-reaction is hydrogen abstraction from the olefinic
substrate. From the results of numerous carbodiazenylation
experiments conducted in aqueous dimethyl sulfoxide, we
have collected experimental data for the degree of hydrogen
abstraction for a series of common types of olefin. The
maximum values given in Figure 1 are helpful for predicting
complications in experiments with unknown substrates.[34]
The maximum value of 10% for allyl acetate (3b) indicates
that usually more than 90% of the aryl radicals undergo
addition to the double bond and that less than 10% are
reduced by hydrogen abstraction from the allylic position
from the olefin. In contrast, as few as 20% of the aryl radi-
cals add to α,β-dimethallyl alcohol (3j) and up to 80% sta-
bilize themselves by hydrogen abstraction.
As a first new application of the now readily available β-
Reactive diazonium salts (e.g., the acceptor-substituted salt hydroxyazo compounds (Table 2, Entries 4–6) we investi-
1d), for example, are reduced more rapidly by iron(II) ions gated the synthesis of vinyldiazenes. Mesylation of the
and thus have to be added over a shorter overall period to alcohol 8j, followed by DBU-mediated elimination of 9,
maintain the ideal concentration. Our standard procedure gave the desired diazabutadiene 10 as a yellow solid in 83%
(addition of the diazonium salt over 10 min) was adjusted yield (Scheme 5).[35]
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Carboamination of Non-Activated Olefins
Scheme 5. Synthesis of vinyldiazene 10 and tetrahydropyridazines
11a and 11b.
Scheme 6. Carbodiazenylation of norborna-1,4-diene (3l).
In view of recently growing interest in photoswitchable
compounds,[36] we irradiated the vinyldiazene 10 in deuter-
iobenzene at wavelengths of 419, 350 and 300 nm and found
photochemical E/Z equilibria of 10:1, 2:3 and 3:1, respec-
tively. During the isomerization experiments no degradation
of the azo compound 10 was observed. The decay of the Z
isomer occurred with a half-life of th = 205 min at 23 °C in
deuteriobenzene. Since the vinyldiazene 10 is also a poten-
tial substrate for hetero-Diels–Alder reactions, we treated
10 in three separate attempts with the dienophiles ethyl ac-
rylate (3a), styrene (3k) and furan. After heating for 18 h at
60 °C the tetrahydropyridazines 11a and 11b had formed,
whereas only unchanged starting material was isolated from
the reaction mixture containing furan.[37,38]
later turned out not to be the best choice. High pressures
(up to 100 bar) were sometimes necessary to achieve com-
plete conversion.[41] Moreover, different commercially avail-
able batches of catalyst gave varying outcomes, and workup
and isolation of very hydrophilic products was often
troubled by the formation of complexes with aluminium
ions from the catalyst. Initial experiments with zinc as re-
ductant appeared more promising, and the search for a suit-
able solvent led us to a mixture of acetic acid and dilute
hydrochloric acid. Under these conditions, the azo com-
pounds 12 were cleanly converted into mixtures of amines
14 and anilines 15 (Scheme 7).[42]
Carbodiazenylation of olefins such as norborna-1,4-
diene (3l) by our early procedures would have been difficult
because of the low solubility of the substrate in aqueous
solvents. Moreover, we chose this norbornadiene 3l because
of its particular behaviour in radical reactions. It is known
that after radical addition to the first double bond an equi-
librium between two secondary alkyl radicals A and B is
established (Scheme 6). Although literature precedence[39]
for the trapping of both intermediates exists, the arene-
diazonium salts 1b–d react preferably with intermediate B
to give tricyclanes 12a–c.[40] Only in the attempt with the
most electrophilic diazonium salt 1d were traces of azo
compound 13 found in the crude product mixture.
Scheme 7. Synthesis of 5-aryl-3-tricycloheptylamines 14a–c by car-
boamination of norborna-1,4-diene (3l).
Tricycloheptylamines of type 14 have so far not been de-
The products from the three experiments vary only in the scribed. One possible route by reductive amination of the
sense that a 1:1 diastereomeric ratio of 12c is obtained from literature-known 5-aryltricycloheptan-3-ones would result
the electrophilic diazonium salt 1d, whereas a ratio of 2:1 in a far more complicated procedure.[43] Because of the
was found for both 12a and 12b. Given the good yields and unique structure, in combination with the defined steric de-
selective formation of product type 12, we decided also to mand, these amines could be valuable building blocks for
use norborna-1,4-diene (3l) in the search for an improved, the synthesis of new biologically active compounds.[44] The
more convenient carboamination procedure. Our previously developed carbodiazenylation/hydrogenation sequence of-
reported protocol[26a,26c,26d] for reductive cleavage of the N– fers efficient, quick and variable access (with respect to the
N bond by hydrogenation in the presence of Raney nickel aromatic moiety) to this new class of compounds.
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Competition Experiment Comparing Iodine Transfer and Aryl
Radical Addition to Allyl Acetate: The arenediazonium salt 1b
(0.500 mmol) was decomposed by FeSO4 (1.50 mmol) in the pres-
ence of 2-iodopropane (6, 5.00 mmol), allyl acetate (3b, 5.00, 10.0,
20.0, 40.0 mmol) and TEMPO (4, 2.00 mmol) in DMSO/water
(10:1, v/v, 10.0 mL). After the system had been stirred at room
temp. for 10 min, ascorbic acid (3.0 mmol) was added and stirring
was continued for a further 10 min. Aqueous workup followed by
extraction with diethyl ether and removal of excess olefin and iodo-
propane under reduced pressure gave a product mixture, which was
Conclusions
In summary, we have shown that radical carbodiazenyl-
ation can be developed into a versatile and effective syn-
thetic method. The readily available starting materials and
the use of non-toxic iron salts are favourable both for labo-
ratory and for large-scale applications.[19] The β-arylazo
compounds, which are accessible from aryldiazonium salts
and olefins under simple reaction conditions, give quick ac-
cess to numerous further products including β-arylamines,
amino acids and heterocycles.
1
analysed by H NMR spectroscopy.
4-Iodoanisole (7): Rf = 0.85 (petroleum ether/EtOAc, 4:1). 1H NMR
(250 MHz, C6D6): δ = 3.09 (s, 3 H), 6.30 (d, J = 9.0 Hz, 2 H), 7.34
(d, J = 9.0 Hz, 2 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 54.7
(CH3), 82.9 (Cq), 116.6 (2ϫCH), 138.5 (2ϫCH), 159.8 (Cq) ppm.
GC-MS (EI): m/z (%) = 234 [M]+ (100), 219 (30), 191 (12), 92 (11).
Experimental Section
General Remarks: Solvents and reagents were degassed with argon
prior to use in radical reactions. 1H NMR spectra were recorded
on 250, 360 and 500 MHz spectrometers in CDCl3, CD3OD,
CD3CN and C6D6 as solvents and referenced to TMS (δ = 0 ppm),
CHCl3 (δ = 7.26 ppm), CHD2OD (δ = 3.31 ppm), CHD2CN (δ =
1.94 ppm) or C6HD5 (δ = 7.15 ppm). Chemical shifts are reported
in parts per million (ppm). Coupling constants J are given in Hertz
(Hz). The following abbreviations are used for the description of
signals: s (singlet), d (doublet), dd (double doublet), t (triplet), q
(quadruplet), m (multiplet). 13C NMR spectra were recorded at
62.9 and 90.6 MHz in CDCl3, CD3OD, CD3CN and C6D6 with
CDCl3 (δ = 77.0 ppm), CD3OD (δ = 49.5 ppm), CD3CN (δ =
1.24 ppm) and C6D6 (δ = 128.0 ppm) as standards. Chemical shifts
are given in parts per million (ppm). 19F NMR spectra were re-
corded at 235.3 MHz with CFCl3 (δ = 0 ppm) as standard. Analyti-
cal TLC was carried out on Merck silica gel plates with use of
short-wave UV light (254 nm) to visualize components. Silica gel
(Kieselgel 60, 40–63 µm, Merck) was used for flash column
chromatography. Arenediazonium tetrafluoroborates were pre-
pared by previously reported procedures.[45]
General Procedure for Carbodiazenylation: DMSO/H2O (6.0 mL,
5:2, v/v, mixture, previously degassed with argon), olefin
(12.0 mmol, 6 equiv.) and FeSO4·7H2O (1.67 g, 6.00 mmol,
3 equiv.) were introduced into an argon-filled 50 mL Schlenk flask
fitted with argon balloon and rubber septum. A solution of the
diazonium salt (2.00 mmol, 1 equiv.) in DMSO/H2O (3.0 mL, 5:2,
v/v, mixture, previously degassed with argon) was added dropwise
by syringe over a period of 10 min. The reaction mixture was
stirred for 10 more min at room temp., and was then diluted with
water (50 mL) and extracted with Et2O (3ϫ50 mL). The combined
ethereal extracts were washed with satd. aq. NaCl and dried with
Na2SO4. Careful evaporation of the solvent gave the carbodiazenyl-
ation products as yellow oils, which were further purified by col-
umn chromatography.
Among the carbodiazenylation products, the β-hydroxy azo com-
pounds arising from β-methallyl alcohol (Table 1, Entries 1–3) and
allyl alcohol (Table 2, Entries 4–6) are particularly labile since they
can decompose by fragmentation and isomerization. To prevent
these side reactions, the crude product mixture should be heated in
the water bath as briefly as possible during evaporation of the sol-
vents and the silica gel used for column chromatography should be
deactivated prior to use with triethylamine. Both isomerization and
fragmentation occur especially quickly when the diazonium salts
bear electron-withdrawing substituents.
Competition Experiment Comparing Aryl Radical Addition to Ethyl
Acrylate and to Allyl Acetate: The arenediazonium salts 1a and 1b
(1.00 mmol) were decomposed with FeSO4·7H2O (3.00 mmol) in
the presence of ethyl acrylate (10.0 mmol), allyl acetate (10.0 mmol)
and TEMPO (3.00 mmol) in DMSO/water (5:1, 10.0 mL). After
addition of ascorbic acid (3 mmol), aqueous workup, extraction
with diethyl ether and removal of excess olefin under reduced pres-
3-(4-Methoxyphenyl)-2-(4-methoxyphenylazo)-2-methylpropan-1-ol
(8a): Yield 242 mg (0.77 mmol, 77%). For analytical data, see
ref.[26b]
1
sure, the product mixture was analysed by H NMR spectroscopy.
3-(4-Fluorophenyl)-2-(4-fluorophenylazo)-2-methylpropan-1-ol (8b):
Yield 192 mg (0.66 mmol, 66%). Yellow oil. Rf = 0.50 (petroleum
ether/EtOAc, 4:1). 1H NMR (250 MHz, CDCl3): δ = 1.22 (s, 3 H),
3.00 (d, J = 11.8 Hz, 1 H), 3.13 (d, J = 11.8 Hz, 1 H), 3.71 (d, J =
11.8 Hz, 1 H), 3.79 (d, J = 11.8 Hz, 1 H), 6.95 (dd, JH,F = 8.9, J
= 8.9 Hz, 2 H), 7.11–7.21 (m, 4 H), 7.71 (dd, JH,F = 5.2, J = 8.9 Hz,
2 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 19.5 (CH3), 40.5
In the photochemical experiment, a solution of carbodiazone 2
(120 mg, 0.500 mmol) and TEMPO (1.50 mmol) in dichlorometh-
ane (5 mL), ethyl acrylate (1.00 mL, 10.0 mmol) and allyl acetate
(1.00 mL, 10.0 mmol) was irradiated at 350 nm (Rayonet photore-
actor) for 120 min. After addition of ascorbic acid (3 mmol), aque-
ous workup, extraction with diethyl ether and removal of excess
olefin under reduced pressure, the product mixture was analysed
2
1
(CH2), 66.8 (CH2), 73.7 (Cq), 114.8 (d, JC,F = 21.1 Hz, 2ϫCH),
by H NMR spectroscopy.
2
3
115.9 (d, JC,F = 22.8 Hz, 2ϫCH), 124.1 (d, JC,F = 8.9 Hz,
Ethyl 3-Phenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)propionate
3
4
2ϫCH), 132.1 (d, JC,F = 7.9 Hz, 2ϫCH), 132.5 (d, JC,F
3.3 Hz, 2ϫCq), 148.0 (d, JC,F = 3.0 Hz, 2ϫCq), 161.7 (d, JC,F
=
=
(5a): For analytical data, see ref.[31]
4
1
244.5 Hz, 2ϫCq), 164.2 (d, JC,F = 251.4 Hz, 2ϫCq) ppm. 19F
NMR (235 MHz, CDCl3): δ = –110.2, –117.2 ppm. MS (ESI): m/z
(%) = 291 [M + H]+. HRMS (ESI): calcd. for C16H17N2OF2 [M +
H]+: 291.1303; found 291.1305.
1
3-Phenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)propyl
Acetate
(5b): For analytical data, see ref.[31]
Ethyl 3-(4-Methoxyphenyl)-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)-
propionate (5c): For analytical data, see ref.[31]
Methyl 2-[1-Hydroxymethyl-2-(2-methoxycarbonylphenyl)-1-methyl-
ethylazo]benzoate (8c): Yield 260 mg (0.70 mmol, 70%). Yellow oil.
Rf = 0.30 (petroleum ether/EtOAc, 3:1). 1H NMR (250 MHz,
3-(4-Methoxyphenyl)-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)propyl
Acetate (5d): For analytical data, see ref.[31]
3184
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3179–3189

Carboamination of Non-Activated Olefins
CDCl3): δ = 1.12 (s, 3 H), 3.37 (d, J = 13.4 Hz, 1 H), 3.60–3.75 (m, Methyl 2-[3-Acetoxy-2-(2-methoxycarbonylphenylazo)propyl]benzo-
2 H), 3.63 (s, 3 H), 3.76 (s, 3 H), 3.83 (d, J = 13.4 Hz, 1 H), 7.00
ate (8i): Yield 310 mg (0.78 mmol, 78%). For analytical data, see
(dd, J = 1.4, J = 7.9 Hz, 1 H), 7.11–7.37 (m, 4 H), 7.41–7.48 (m, 1 ref.[26b]
H), 7.71 (dd, J = 1.1, J = 7.8 Hz, 1 H), 7.82 (dd, J = 1.4, J =
3-(4-Methoxyphenyl)-2-(4-methoxyphenylazo)propan-1-ol (8j): Yield
7.7 Hz, 1 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 19.3 (CH3),
37.8 (CH2), 51.8 (CH3), 52.6 (CH3), 66.3 (CH2), 75.8 (Cq), 117.8
(CH), 126.0 (Cq), 126.3 (CH), 129.2 (CH), 130.3 (CH), 130.4 (CH),
131.1 (CH), 131.7 (Cq), 133.0 (CH), 133.3 (CH), 138.1 (Cq), 152.5
(Cq), 166.7 (Cq), 168.6 (Cq) ppm. MS (ESI): m/z (%) = 371 [M +
H]+. HRMS (ESI): calcd. for C20H23N2O5 [M + H]+: 371.1602;
found 371.1605.
248 mg (0.83 mmol, 83%). Yellow oil. Rf = 0.30 (petroleum ether/
1
EtOAc, 2:1). H NMR (360 MHz, C6D6): δ = 3.03 (dd, J = 7.3, J
= 14.0 Hz, 1 H), 3.15 (dd, J = 6.8, J = 14.0 Hz, 1 H), 3.20 (s, 3 H),
3.29 (s, 3 H), 3.83 (dd, J = 3.6, J = 11.3 Hz, 1 H), 3.93 (dd, J =
6.6, J = 11.3 Hz, 1 H), 4.12–4.19 (m, 1 H), 6.70 (d, J = 9.1 Hz, 2
H), 6.73 (d, J = 9.5 Hz, 2 H), 7.05 (d, J = 9.5 Hz, 2 H), 7.79 (d, J
= 9.1 Hz, 2 H) ppm. 13C NMR (91 MHz, C6D6): δ = 35.9 (CH2),
54.7 (CH3), 55.0 (CH3), 63.7 (CH2), 79.9 (CH), 114.3 (2ϫCH),
114.4 (2ϫCH), 124.6 (2ϫCH), 130.6 (Cq), 130.9 (2ϫCH), 146.8
(Cq), 158.8 (Cq), 162.2 (Cq) ppm. MS (ESI): m/z (%) = 301 [M +
H]+. HRMS (ESI): calcd. for C17H21N2O3 [M + H]+: 301.1547;
found 301.1553.
3-(4-Methoxyphenyl)-2-(4-methoxyphenylazo)-2-methylpropyl Ace-
tate (8d): Yield 276 mg (0.78 mmol, 78%). For analytical data, see
ref.[26b]
3-(4-Fluorophenyl)-2-(4-fluorophenylazo)-2-methylpropyl
Acetate
(8e): Yield 302 mg (0.91 mmol, 91%). Yellow oil. Rf = 0.80 (petro-
1
3-(4-Fluorophenyl)-2-(4-fluorophenylazo)propan-1-ol (8k): Yield
221 mg (0.80 mmol, 80%). Yellow oil. Rf = 0.60 (petroleum ether/
leum ether/EtOAc, 4:1). H NMR (250 MHz, CDCl3): δ = 1.24 (s,
3 H), 2.05 (s, 3 H), 3.10 (d, J = 15.4 Hz, 1 H), 3.16 (d, J = 15.4 Hz,
1 H), 4.32 (d, J = 11.2 Hz, 1 H), 4.37 (d, J = 11.2 Hz, 1 H), 6.91
(d, JH,F = 8.7, J = 8.7 Hz, 2 H), 7.04 (dd, JH,F = 5.5, J = 8.7 Hz,
2 H), 7.13 (dd, JH,F = 8.7, J = 8.7 Hz, 2 H), 7.68 (dd, JH,F = 5.2,
J = 8.7 Hz, 2 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 19.8
(CH3), 20.8 (CH3), 41.3 (CH2), 67.8 (CH2), 72.1 (Cq), 114.8 (d,
2JC,F = 21.2 Hz, 2ϫCH), 115.8 (d, 2JC,F = 22.8 Hz, 2ϫCH); 124.1
1
EtOAc, 2:1). H NMR (360 MHz, C6D6): δ = 2.92 (dd, J = 6.8, J
= 14.0 Hz, 1 H), 3.00 (dd, J = 7.4, J = 14.0 Hz, 1 H), 3.75 (dd, J
= 4.1, J = 11.3 Hz, 1 H), 3.85 (dd, J = 6.7, J = 11.3 Hz, 1 H), 3.99–
4.04 (m, 1 H), 6.70–6.76 (m, 4 H), 6.84 (dd, JH,F = 5.5, J = 8.6 Hz,
2 H), 7.53 (dd, JH,F = 5.2, J = 8.9 Hz, 2 H) ppm. 13C NMR
(91 MHz, C6D6): δ = 35.5 (CH2), 63.3 (CH2), 79.8 (CH), 115.4 (d,
2JC,F = 21.1 Hz, 2ϫCH), 116.1 (d, 2JC,F = 22.8 Hz, 2ϫCH), 124.7
3
3
(d, JC,F = 8.9 Hz, 2ϫCH), 132.0 (d, JC,F = 7.9 Hz, 2ϫCH),
3
3
4
4
(d, JC,F = 8.9 Hz, 2ϫCH), 131.3 (d, JC,F = 7.6 Hz, 2ϫCH),
132.1 (d, JC,F = 3.3 Hz, 2ϫCq); 148.2 (d, JC,F = 3.1 Hz, 2ϫCq);
4
4
1
1
134.1 (d, JC,F = 3.3 Hz, Cq), 148.7 (d, JC,F = 3.0 Hz, Cq), 162.1
(d, 1JC,F = 244.2 Hz, Cq), 164.5 (d, 1JC,F = 251.1 Hz, Cq) ppm. MS
(ESI): m/z (%) = 277 [M + H]+. HRMS (ESI): calcd. for
C15H15N2OF2 [M + H]+: 277.1147; found 277.1148.
161.7 (d, JC,F = 244.8 Hz, 2ϫCq), 164.1 (d, JC,F = 251.0 Hz,
2ϫCq), 170.7 (Cq) ppm. 19F NMR (235 MHz, CDCl3): δ = –110.7,
–117.0 ppm. MS (ESI): m/z (%) = 333 [M + H]+. HRMS (ESI):
calcd. for C18H19N2O2F2 [M + H]+: 333.1409; found 333.1411.
Methyl 2-[2-(2-Methoxycarbonylphenyl)-1-hydroxymethylethylazo]-
benzoate (8l): Yield 231 mg (0.65 mmol, 65%). Yellow oil. Rf = 0.50
(petroleum ether/EtOAc, 2:1). 1H NMR (360 MHz, C6D6): δ = 3.41
(s, 3 H), 3.45 (s, 3 H), 3.63 (dd, J = 6.6, J = 13.2 Hz, 1 H), 3.83
(dd, J = 7.4, J = 13.2 Hz, 1 H), 4.05–4.14 (m, 2 H), 4.61–4.69 (m,
1 H), 6.87–6.97 (m, 2 H), 7.02–7.08 (m, 3 H), 7.18 (dd, J = 1.0, J
= 7.7 Hz, 1 H), 7.63 (d, J = 6.6 Hz, 1 H), 7.90 (d, J = 1.2, J =
7.8 Hz, 1 H) ppm. 13C NMR (91 MHz, C6D6): δ = 34.7 (CH2), 51.5
(CH3), 52.1 (CH3), 63.0 (CH2), 80.5 (CH), 119.2 (CH), 126.3 (Cq),
126.6 (CH), 128.8 (CH), 130.3 (CH), 130.5 (Cq), 131.3 (CH), 132.0
(CH), 132.7 (CH), 132.9 (CH), 141.2 (Cq), 153.8 (Cq), 166.9 (Cq),
167.7 (Cq) ppm. MS (ESI): m/z (%) = 357 [M + H]+. HRMS (ESI):
calcd. for C19H21N2O5 [M + H]+: 357.1445; found 357.1446.
Methyl 2-[1-Acetoxymethyl-2-(2-methoxycarbonylphenyl)-1-methyl-
ethylazo]benzoate (8f): Yield 340 mg (0.83 mmol, 83%). Yellow oil.
Rf = 0.50 (petroleum ether/EtOAc, 4:1). 1H NMR (250 MHz,
CDCl3): δ = 1.14 (s, 3 H), 1.95 (s, 3 H), 3.65 (s, 3 H), 3.65 (d, J =
13.6 Hz, 1 H), 3.67 (s, 3 H), 3.74 (d, J = 13.6 Hz, 1 H), 4.26 (d, J
= 11.2 Hz, 1 H), 4.33 (d, J = 11.2 Hz, 1 H), 7.06–7.13 (m, 2 H),
7.15–7.22 (m, 1 H), 7.24–7.31 (m, 1 H), 7.32–7.40 (m, 1 H), 7.42–
7.50 (m, 1 H), 7.71 (dd, J = 1.7, J = 7.5 Hz, 1 H), 7.73 (dd, J =
1.6, J = 7.3 Hz, 1 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 19.2
(CH3), 20.8 (CH3), 38.2 (CH2), 51.8 (CH3), 52.1 (CH3), 68.1 (CH2),
73.6 (Cq), 118.0 (CH), 126.5 (CH), 127.8 (Cq), 129.2 (CH), 129.7
(CH), 130.3 (CH), 131.1 (CH), 131.7 (Cq), 132.1 (CH), 133.0 (CH),
137.6 (Cq), 151.6 (Cq), 167.4 (Cq), 168.4 (Cq), 170.7 (Cq) ppm. MS
(ESI): m/z (%) = 413 [M + H]+. HRMS (ESI): calcd. for
C22H25N2O6 [M + H]+: 413.1708; found 413.1706.
4-(4-Methoxyphenyl)-3-(4-methoxyphenylazo)butan-1-ol (8m): Yield
238 mg (0.76 mmol, 76%). For analytical data, see ref.[26b]
3-(4-Methoxyphenyl)-2-(4-methoxyphenylazo)propyl Acetate (8 g):
Synthesis of Vinyldiazene 10 By Mesylation of 8j and Elimination
from 9: Mesyl chloride (0.39 mL, 0.57 g, 5.0 mmol, 2.5 equiv.) and
NEt3 (1.1 mL, 0.81 g, 8.0 mmol, 4.0 equiv.) were added at 0 °C to
a solution of 8j (0.601 g, 2.00 mmol) in CH2Cl2 (20 mL). The re-
sulting mixture was stirred at room temp. over 2 h, and was then
washed with satd. aq. KHSO4 and NaHCO3. After the system had
been dried over Na2SO4 and filtered, DBU (0.60 mL, 4.0 mmol,
2.0 equiv.) was added at 0 °C to the solution of 9, and the resulting
mixture was left to come to room temp. over 2 h. After washing
with satd. aq. KHSO4 the organic phase was dried with Na2SO4
and quickly concentrated under reduced pressure. Immediate puri-
fication by column chromatography gave 10 as a yellow solid
(468 mg, 1.66 mmol, 83%). Compound 10 is stable in the pure state
when stored below 0 °C. The crude product decomposes in concen-
trated solution within several hours.
Yield 273 mg (0.80 mmol, 80%). For analytical data, see ref.[26b]
3-(4-Fluorophenyl)-2-(4-fluorophenylazo)propyl Acetate (8h): Yield
258 mg (0.81 mmol, 81%). Yellow oil. Rf = 0.65 (petroleum ether/
EtOAc, 4:1). 1H NMR (360 MHz, C6D6): δ = 1.57 (s, 3 H), 2.75
(dd, J = 6.5, J = 14.0 Hz, 1 H), 2.90 (dd, J = 7.6, J = 14.0 Hz, 1
H), 4.14–4.20 (m, 1 H), 4.35 (dd, J = 3.8, J = 11.5 Hz, 1 H), 4.54
(dd, J = 8.1, J = 11.5 Hz, 1 H), 6.67–6.74 (m, 6 H), 7.53 (dd, JH,F
= 5.2, J = 9.0 Hz, 2 H) ppm. 13C NMR (91 MHz, C6D6): δ = 20.2
2
(CH3), 35.9 (CH2), 64.6 (CH2), 77.1 (CH), 115.5 (d, JC,F
=
2
21.2 Hz, 2ϫCH), 116.1 (d, JC,F = 22.9 Hz, 2ϫCH), 124.8 (d,
3JC,F = 8.9 Hz, 2ϫCH), 131.2 (d, JC,F = 7.8 Hz, 2ϫCH), 133.2
3
(d, 4JC,F = 3.3 Hz, Cq), 148.7 (d, 4JC,F = 3.0 Hz, Cq), 162.1 (d, 1JC,F
1
= 244.6 Hz, Cq), 164.5 (d, JC,F = 251.1 Hz, Cq), 169.9 (Cq) ppm.
19F NMR (235 MHz, C6D6): δ = –109.7, –116.3 ppm. MS (ESI):
m/z (%) = 319 [M + H]+. HRMS (ESI): calcd. for C17H17N2O2F2
[M + H]+: 319.1253; found 319.1254.
3-(4-Methoxyphenyl)-2-(4-methoxyphenylazo)propyl
Methanesul-
1
fonate (9): Yellow oil. Rf = 0.40 (petroleum ether/EtOAc, 2:1). H
Eur. J. Org. Chem. 2008, 3179–3189
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3185

O. Blank, A. Wetzel, D. Ullrich, M. R. Heinrich
FULL PAPER
NMR (360 MHz, C6D6): δ = 2.11 (s, 3 H), 2.86 (dd, J = 7.0, J =
13.7 Hz, 1 H), 2.98 (dd, J = 7.3, J = 13.7 Hz, 1 H), 3.18 (s, 3 H),
3.25 (s, 3 H), 4.22 (m, 1 H), 4.36 (dd, J = 3.7, J = 10.6 Hz, 1 H),
25.2 (CH2), 43.8 (CH2), 55.2 (CH3), 55.4 (CH), 55.6 (CH3), 113.7
(2ϫCH), 114.3 (2ϫCH), 114.4 (2ϫCH), 126.1 (2ϫCH), 126.8
(CH), 128.5 (2ϫCH), 129.7 (2ϫCH), 130.5 (Cq), 141.4 (Cq), 141.5
4.57 (dd, J = 7.3, J = 10.6 Hz, 1 H), 6.67 (d, J = 9.0 Hz, 2 H), 6.68 (Cq), 143.3 (Cq), 152.9 (Cq), 158.1 (Cq) ppm. MS (EI): m/z (%) =
(d, J = 8.7 Hz, 2 H), 6.91 (d, J = 8.7 Hz, 2 H), 7.78 (d, J = 9.0 Hz,
386 (4) [M]+, 288 (6), 267 (7), 250 (6), 161 (19), 152 (42), 135 (100),
2 H) ppm. MS (EI): m/z (%) = 378 [M]+ (1), 348 (1), 312 (8), 320 122 (23), 121 (26), 107 (17), 105 (85), 77 (57). HRMS (EI): calcd.
(37), 319 (19), 305 (10), 279 (13), 244 (11), 189 (13), 148 (23), 147
(26), 136 (16), 135 (41), 123 (43), 121 (88), 109 (81), 108 (46), 107
(34), 97 (27), 80 (25), 79 (100), 77 (25).
for C25H26N2O2 [M]+: 386.1994; found 390.1999.
(4-Methoxyphenyl)[5-(4-methoxyphenyl)tricyclo[2.2.1.02,6]hept-3-yl]-
diazene (12a): This compound was isolated as a 2:1 mixture of
diastereoisomers. Yield 217 mg (0.65 mmol, 65%). Yellow oil. Rf =
0.50 (petroleum ether/EtOAc, 10:1). 1H NMR (500 MHz, C6D6,
major isomer): δ = 1.35–1.55 (m, 4 H), 2.20–2.23 (m, 2 H), 2.94
(br. s, 1 H), 3.20 (s, 3 H), 3.36 (s, 3 H), 4.14 (“t”, J = 1.5 Hz, 1 H),
6.74 (d, J = 9.0 Hz, 2 H), 6.82 (d, J = 8.5 Hz, 2 H), 7.08 (d, J =
(E)-[1-(4-Methoxybenzyl)vinyl](4-methoxyphenyl)diazene [(E)-10]:
Yellow solid, m.p. 78–81 °C, Rf = 0.80 (petroleum ether/EtOAc,
1
3:1). H NMR (360 MHz, C6D6): δ = 3.19 (s, 3 H), 3.31 (s, 3 H),
3.85 (s, 2 H), 5.55 (s, 1 H), 6.27 (s, 1 H), 6.72 (d, J = 9.0 Hz, 2 H),
6.76 (d, J = 8.5 Hz, 2 H), 7.08 (d, J = 8.5 Hz, 2 H), 7.97 (d, J =
9.0 Hz, 2 H) ppm. 13C NMR (91 MHz, C6D6): δ = 34.8 (CH2), 54.7
(CH3), 54.9 (CH3), 114.2 (2ϫCH), 114.5 (2ϫCH), 124.2 (CH2),
125.0 (2ϫCH), 130.7 (2ϫCH), 131.2 (Cq), 147.1 (Cq), 158.7 (Cq),
162.4 (Cq), 162.8 (Cq) ppm. MS (ESI): m/z (%) = 283 [M + H]+.
HRMS (ESI): calcd. for C17H18N2O2 [M + H]+: 283.1441; found
283.1446.
1
8.5 Hz, 2 H), 7.91 (d, J = 9.0 Hz, 2 H) ppm. H NMR (500 MHz,
C6D6, major isomer): δ = 1.19 (d, J = 10.8 Hz, 1 H), 1.30 (“t”, J
= 5.1 Hz, 1 H), 1.45–1.60 (m, 3 H), 2.26 (br. s, 1 H), 3.20 (s, 3 H),
3.35 (s, 3 H), 4.12 (“t”, J = 1.5 Hz, 1 H), 4.17 (br. s, 1 H), 6.75 (d,
J = 9.0 Hz, 2 H), 6.82 (d, J = 8.6 Hz, 2 H), 7.16 (m, 2 H), 7.95 (d,
J = 9.0 Hz, 2 H) ppm. 13C NMR (63 MHz, C6D6, major isomer):
δ = 11.8 (CH), 16.9 (CH), 17.5 (CH), 26.6 (CH2), 42.0 (CH), 48.0
(CH), 54.8 (CH3), 54.9 (CH3), 82.8 (CH), 113.9 (2ϫCH), 114.3
(2ϫCH), 124.6 (2ϫCH), 129.1 (2ϫCH), 133.3 (Cq), 147.2 (Cq),
158.8 (Cq), 161.9 (Cq) ppm. 13C NMR (63 MHz, C6D6, minor iso-
mer): δ = 13.8 (CH), 15.3 (CH), 17.7 (CH), 29.1 (CH2), 42.2 (CH),
45.9 (CH), 54.8 (CH3), 54.9 (CH3), 83.5 (CH), 113.9 (2ϫ CH),
114.4 (2ϫCH), 124.7 (2ϫCH), 129.3 (2ϫCH), 134.0 (Cq), 147.3
(Cq), 158.7 (Cq), 162.0 (Cq) ppm. MS (EI): m/z (%) = 334 (44)
[M]+, 242 (23), 214 (18), 212 (19), 199 (71), 184 (14), 171 (13), 158
(12), 139 (12), 135 (55), 122 (26), 121 (100), 107 (78), 91 (44), 77
(34). HRMS (EI): calcd. for C21H22N2O2: 334.1681; found
334.1676.
Photochemical Isomerization of Vinyldiazene 10: Photoisomeriza-
tion (solutions in C6D6) was carried out in Rayonet photoreactors
at 419, 350 and 300 nm. The E/Z ratios were determined by 1H
NMR spectroscopy.
(Z)-[1-(4-Methoxybenzyl)vinyl](4-methoxyphenyl)diazene [(Z)-10]:
1H NMR (250 MHz, C6D6): δ = 3.17 (s, 3 H), 3.26 (s, 3 H), 3.36
(br. s, 2 H), 4.25 (t, J = 1.5 Hz, 1 H), 4.35 (t, J = 0.8 Hz, 1 H),
6.58 (d, J = 9.0 Hz, 2 H), 6.71 (d, J = 8.8 Hz, 2 H), 6.92 (d, J =
8.8 Hz, 2 H), 6.96 (d, J = 8.8 Hz, 2 H) ppm. 13C NMR (91 MHz,
C6D6): δ = 38.2 (CH2), 54.7 (CH3), 54.9 (CH3), 101.9 (CH2), 113.9
(2ϫCH), 114.3 (2ϫCH), 122.2 (2ϫCH), 130.7 (2ϫCH), 130.8
(Cq), 147.9 (Cq), 159.1 (Cq), 159.4 (Cq), 162.3 (Cq) ppm.
(4-Fluorophenyl)[5-(4-fluorophenyl)tricyclo[2.2.1.02,6]hept-3-yl]di-
azene (12b): This compound was isolated as a 2:1 mixture of dia-
stereoisomers. Yield 196 mg (0.63 mmol, 63%). Yellow oil. Rf =
0.80 (petroleum ether/EtOAc, 10:1). 1H NMR (500 MHz, C6D6,
major isomer): δ = 1.22–1.40 (m, 4 H), 2.02–2.06 (m, 2 H), 2.76 (s,
1 H), 3.99 (br. s, 1 H), 6.73–6.97 (m, 6 H), 7.65 (dd, JH,F = 5.2, J
Diels–Alder Reactions of Vinyldiazene 10: A mixture of vinyldiaz-
ene 10 (0.141 g, 0.500 mmol) and the dienophile (3.0 mL) was
warmed to 60 °C for 18 h. The reaction with ethyl acrylate (3a) was
complete at that time, the mixture with styrene (3k) showed ca.
30% of unreacted starting material, and the attempt with furan
remained unsuccessful. Excess dienophile was removed under re-
duced pressure and the residue was purified by column chromatog-
raphy.
1
= 8.9 Hz, 2 H) ppm. H NMR (500 MHz, C6D6, minor isomer): δ
= 1.10 (td, J = 1.3, J = 10.9 Hz, 1 H), 1.22–1.40 (m, 4 H), 2.08 (s,
1 H), 3.92 (s, 1 H), 3.98 (br. s, 1 H), 6.73–6.90 (m, 4 H), 6.95 (ddd,
J = 0.7, JH,F = 5.5, J = 8.8 Hz, 2 H), 7.69 (dd, JH,F = 5.2, J =
9.0 Hz, 2 H) ppm. 13C NMR (63 MHz, CDCl3, major isomer): δ =
11.6 (CH), 16.7 (CH), 17.4 (CH), 26.4 (CH2), 41.8 (CH), 47.8 (CH),
Ethyl 6-(4-Methoxybenzyl)-2-(4-methoxyphenyl)-2,3,4,5-tetrahydro-
pyridazine-3-carboxylate (11a): Yield 126 mg (0.33 mmol, 66%).
1
Colourless oil. Rf = 0.60 (petroleum ether/EtOAc, 3:1). H NMR
2
2
82.8 (CH), 115.0 (d, JC,F = 21.0 Hz, 2ϫCH), 116.0 (d, JC,F
=
(250 MHz, CDCl3): δ = 1.17 (t, J = 7.1 Hz, 3 H), 1.98–2.08 (m, 3
H), 2.26–2.33 (m, 1 H), 3.54 (s, 2 H), 3.78 (m, 3 H), 3.79 (m, 3 H),
4.13 (dq, J = 1.0, J = 7.1 Hz, 2 H), 4.52–4.58 (m, 1 H), 6.84 (d, J
= 8.8 Hz, 2 H), 6.86 (d, J = 9.3 Hz, 2 H), 7.14 (d, J = 9.3 Hz, 2
H), 7.20 (d, J = 8.8 Hz, 2 H) ppm. 13C NMR (63 MHz, CDCl3): δ
= 14.1 (CH3), 20.2 (CH2), 21.1 (CH2), 43.7 (CH2), 54.6 (CH), 55.2
(CH3), 55.6 (CH3), 61.1 (CH2), 113.8 (2ϫCH), 114.3 (2ϫCH),
115.1 (2ϫCH), 129.8 (2ϫCH), 130.3 (Cq), 141.6 (Cq), 143.5 (Cq),
153.5 (Cq), 158.2 (Cq), 171.7 (Cq) ppm. MS (EI): m/z (%) = 382
[M]+ (20), 309 (38), 262 (7), 206 (17), 122 (14), 121 (100). HRMS
(EI): calcd. for C22H26N2O4 [M]+: 382.1893; found 390.1892.
22.8 Hz, 2ϫCH), 124.7 (d, 3JC,F = 8.8 Hz, 2ϫCH), 129.5 (d, 3JC,F
4
4
= 7.8 Hz, 2ϫCH), 136.7 (d, JC,F = 3.2 Hz, Cq), 149.1 (d, JC,F
=
=
3.1 Hz, Cq), 162.0 (1JC,F = 243.8 Hz, Cq), 164.3 (d, JC,F
1
250.4 Hz, Cq) ppm. 13C NMR (63 MHz, CDCl3, minor isomer): δ
= 13.7 (CH), 15.0 (CH), 17.6 (CH), 28.9 (CH2), 42.0 (CH), 45.8
(CH), 83.5 (CH), 114.9 (d, 2JC,F = 21.0 Hz, 2ϫCH), 116.1 (d, 2JC,F
3
= 22.8 Hz, 2ϫCH), 124.8 (d, JC,F = 8.7 Hz, 2ϫCH), 129.6 (d,
3JC,F = 7.6 Hz, 2ϫCH), 137.4 (d, JC,F = 3.2 Hz, Cq), 149.2 (d,
4
4JC,F = 3.0 Hz, Cq), 161.9 (d, 1JC,F = 243.4 Hz, Cq), 164.4 (d, 1JC,F
= 250.5 Hz, Cq) ppm. MS (EI): m/z (%) = 310 (19) [M]+, 234 (4),
220 (5), 218 (11), 205 (9), 200 (10), 190 (20), 188 (14), 187 (35), 172
(6), 159 (16), 146 (6), 123 (16), 109 (100), 107 (14), 95 (44), 91
(19), 79 (21). HRMS (EI): calcd. for C19H16F2N2: 310.1281; found
310.1280.
3-(4-Methoxybenzyl)-1-(4-methoxyphenyl)-6-phenyl-1,4,5,6-tetra-
hydropyridazine (11b): Yield 98 mg, 0.26 mmol, 51 %. Colourless
1
oil. Rf = 0.70 (petroleum ether/EtOAc, 4:1). H NMR (250 MHz,
CDCl3): δ = 1.61–1.76 (m, 1 H), 1.86–1.98 (m, 1 H), 2.05–2.15 (m,
2 H), 3.57 (s, 2 H), 3.74 (s, 3 H), 3.79 (s, 3 H), 5.06 (t, J = 3.3 Hz, Methyl 2-[5-(2-Methoxycarbonylphenyl)tricyclo[2.2.1.02,6]hept-3-yl-
1 H), 6.81 (d, J = 9.3 Hz, 2 H), 6.84 (d, J = 9.0 Hz, 2 H), 7.09–
azo]benzoate (12c): This compound was isolated as a 1:1 mixture
of diastereoisomers. Yield 164 mg (0.42 mmol, 42%). Yellow oil. Rf
7.33 (m, 9 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 19.4 (CH2),
3186
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Eur. J. Org. Chem. 2008, 3179–3189

Carboamination of Non-Activated Olefins
1
= 0.30 (petroleum ether/EtOAc, 10:1). H NMR (360 MHz, C6D6,
H) ppm. 13C NMR (91 MHz, CDCl3, major isomer): δ = 10.3
mixture of diastereoisomers): δ = 1.09 (d, J = 11.3 Hz, 1 H), 1.26–
1.34 (m, 4 H), 1.38–1.54 (m, 4 H), 2.07 (d, J = 10.9 Hz, 1 H), 2.40 58.6 (CH), 115.1 (d, JC,F = 21.0 Hz, 2ϫCH), 129.4 (d, JC,F
(br. s, 1 H), 2.66 (br. s, 1 H), 3.41 (s, 3 H), 3.47 (s, 3 H), 3.55 (s, 3 7.7 Hz, 2ϫCH), 137.6 (d, JC,F = 3.1 Hz, Cq), 161.8 (d, JC,F
(CH), 16.7 (CH), 18.6 (CH), 24.8 (CH2), 42.8 (CH), 47.0 (CH),
2
3
=
=
4
1
H), 3.57 (s, 3 H), 3.97 (br. s, 1 H), 4.12 (“t”, J = 1.4 Hz, 1 H), 4.35
(“t”, J = 1.6 Hz, 1 H), 4.80 (br. s, 1 H), 6.88–7.04 (m, 5 H), 7.10–
243.7 Hz, Cq) ppm. 13C NMR (91 MHz, CDCl3, minor isomer): δ
= 13.6 (CH), 14.0 (CH), 18.8 (CH), 28.4 (CH2), 42.8 (CH), 44.2
7.21 (m, 3 H), 7.26 (dd, J = 1.1, J = 7.7 Hz, 1 H), 7.38–7.49 (m, 2 (CH), 59.3 (CH), 115.1 (d, 2JC,F = 21.0 Hz, 2ϫCH), 129.6 (d, 3JC,F
4
1
H), 7.56–7.69 (m, 3 H), 7.88 (dd, J = 1.5, J = 8.0 Hz, 1 H), 7.91 = 7.7 Hz, 2ϫCH), 137.7 (d, JC,F = 3.1 Hz, Cq), 161.7 (d, JC,F
=
(dd, J = 1.4, J = 7.8 Hz, 1 H) ppm. 13C NMR (90 MHz, C6D6,
mixture of diastereoisomers): δ = 12.5 (CH), 14.4 (CH), 15.5 (CH),
243.7 Hz, Cq) ppm. MS (EI): m/z (%) = 203 (16) [M]+, 187 (15),
186 (100), 185 (34), 171 (11), 160 (12), 159 (12), 146 (7), 137 (8),
17.1 (CH), 17.2 (CH), 17.3 (CH), 26.6 (CH2), 29.1 (CH2), 41.6 133 (8), 120 (7), 11 (14), 109 (12), 107 (10), 94 (7), 66 (49). HRMS
(CH), 42.1 (CH), 44.5 (CH), 46.7 (CH), 51.5 (CH3), 51.6 (CH3), (EI): calcd. for C13H14FN: 203.1110; found 203.1106.
51.8 (CH3), 51.9 (CH3), 83.8 (CH), 84.5 (CH), 119.5 (CH), 120.3
Methyl 4-(5-Aminotricyclo[2.2.1.02,6]hept-3-yl)benzoate (14c): This
compound was isolated as a 1:1 mixture of diastereoisomers. Yield
(CH), 126.3 (CH), 126.5 (CH), 128.2 (Cq), 128.9 (Cq), 129.0 (CH),
129.1 (CH), 129.2 (CH), 129.3 (CH), 129.7 (CH), 129.8 (CH), 130.2
(Cq), 130.8 (CH), 131.1 (CH), 131.2 (Cq), 131.3 (CH), 131.5 (CH),
131.6 (CH), 131.9 (CH), 142.7 (Cq), 142.8 (Cq), 152.7 (Cq), 152.8
92 mg (0.38 mmol, 38%). Colourless oil. Rf = 0.30 (CHCl3/MeOH
= 20:1, TLC plate deactivated with NEt3). 1H NMR (500 MHz,
CDCl3, mixture of diastereoisomers): δ = 1.10–1.70 (m, 10 H),
2.18–2.21 (m, 2 H), 2.98 (br. s, 1 H), 3.31 (br. s, 1 H), 3.34 (br. s,
1 H), 3.58 (br. s, 1 H), 3.88 (s, 3 H), 3.89 (s, 3 H), 7.24 (d, J =
(Cq), 167.5 (Cq), 167.6 (Cq), 167.7 (Cq), 168.2 (Cq) ppm. MS (EI):
m/z (%) = 391 (8) [M + H]+, 390 (23) [M]+, 359 (4), 298 (8), 240
(7), 227 (44), 196 (17), 195 (100), 177 (27), 167 (28), 165 (22), 163
(18), 161 (58), 152 (21), 149 (15), 135 (36), 109 (10), 105 (12), 91
(18), 85 (15), 77 (22). HRMS (EI): calcd. for C23H22N2O4:
390.1580; found 390.1577.
8.4 Hz, 2 H), 7.34 (d, J = 8.3 Hz, 2 H), 7.89 (d, J = 8.3 Hz, 2 H),
7.93 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR (90 MHz, CDCl3, mixture
of diastereoisomers): δ = 10.8 (CH), 13.4 (CH), 14.0 (CH), 16.1
(CH), 16.7 (CH), 16.9 (CH), 25.4 (CH2), 28.3 (CH2), 40.5 (CH),
40.6 (CH), 45.4 (CH), 47.6 (CH), 51.9 (CH3), 52.0 (CH3), 57.4
(CH), 58.2 (CH), 127.6 (2ϫCH), 127.8 (2ϫCH), 128.1 (Cq), 128.3
(Cq), 129.2 (2ϫCH), 129.3 (2ϫCH), 145.9 (Cq), 146.3 (Cq), 166.9
(Cq), 167.0 (Cq) ppm. MS (EI): m/z (%) = 243 (14) [M]+, 226 (68),
195 (15), 167 (62), 151 (57), 120 (100), 107 (23), 92 (34), 86 (26), 66
(79), 59 (89). HRMS (EI): calcd. for C15H17NO2: 243.1259; found
243.1257.
Carboamination of Norborna-1,4-diene (3l) by a Carbodiazenylation/
Hydrogenation Sequence: The crude carbodiazenylation product
obtained from the arenediazonium tetrafluoroborate (2.00 mmol,
1 equiv.), norborna-1,4-diene (3l, 1.22 mL, 1.10 g, 6 equiv.) and
FeSO4 (1.67 g, 6.00 mmol, 3 equiv., see general procedure described
above) were dissolved in AcOH (10 mL). Zn dust (1.0 g) and aq.
HCl (6 , 10 mL) were added to this solution, and the resulting
mixture was stirred for 4 h at room temp. After dilution with H2O
and addition of aq. NaOH (3 ) to pH Ͼ 12, the aqueous phase
was extracted with Et2O (3ϫ30 mL). The combined extracts were
dried with Na2SO4 and concentrated under reduced pressure. Puri-
fication by column chromatography (silica gel previously deacti-
vated with NEt3) gave the anilines 15 followed by the amines 14.
Acknowledgments
This project was financed by the Fonds der Chemischen Industrie
(Liebig fellowship) and the Deutsche Forschungsgemeinschaft
(DFG). We are thankful to the Ausbildungszentrum (D. U.) of the
Technische Universität München. The generous help and support
of Prof. Dr. Thorsten Bach and his group is gratefully acknowl-
edged.
5-(4-Methoxyphenyl)tricyclo[2.2.1.02.6]hept-3-ylamine (14a): This
compound was isolated as a 2:1 mixture of diastereoisomers. Yield
135 mg (0.63 mmol, 63%). Colourless oil. Rf = 0.50 (CHCl3/MeOH
= 10:1). 1H NMR (250 MHz, CDCl3, major isomer): δ = 1.15–1.45
(m, 5 H), 1.73 (br. s, 1 H), 2.83 (br. s, 1 H), 3.10 (br. s, 1 H), 3.78
(s, 3 H), 6.83 (d, J = 8.8 Hz, 2 H), 7.13 (d, J = 8.8 Hz, 2 H) ppm.
1H NMR (250 MHz, CDCl3, minor isomer): δ = 1.15–1.45 (m, 5
H), 1.69 (br. s, 1 H), 2.89 (br. s, 1 H), 3.26 (br. s, 1 H), 3.79 (s, 3
H), 6.84 (d, J = 8.6 Hz, 2 H), 7.21 (d, J = 8.8 Hz, 2 H) ppm. 13C
NMR (63 MHz, CDCl3, major isomer): δ = 10.5 (CH), 16.4 (CH),
17.3 (CH), 24.9 (CH2), 41.4 (CH), 46.8 (CH), 55.2 (CH3), 57.3
(CH), 113.4 (2ϫCH), 128.5 (2ϫCH), 133.0 (Cq), 158.0 (Cq) ppm.
13C NMR (63 MHz, CDCl3, minor isomer): δ = 13.3 (CH), 14.1
(CH), 14.8 (CH), 28.3 (CH2), 41.4 (CH), 44.1 (CH), 55.2 (CH3),
58.2 (CH), 113.4 (2ϫCH), 128.7 (2ϫCH), 133.0 (Cq), 157.9
(Cq) ppm. MS (ESI): m/z = 216 [M + H]+. HRMS (ESI): calcd. for
C14H18NO [M + H]+: 216.1383; found 216.1383.
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7.15 (dd, JH,F = 5.6, J = 8.4 Hz, 2 H) ppm. H NMR (360 MHz,
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3.29 (br. s, 1 H), 6.95 (dd, JH,F = 8.4, J = 8.4 Hz, 2 H), 7.23 (m, 2
Eur. J. Org. Chem. 2008, 3179–3189
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3187

O. Blank, A. Wetzel, D. Ullrich, M. R. Heinrich
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Received: March 5, 2008
Published Online: May 8, 2008
Eur. J. Org. Chem. 2008, 3179–3189
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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