A new method for the synthesis of nonsymmetrically substituted bis(azulen-1-yl) ketones

Article abstract of DOI:10.1002/hlca.201000032

The 1-(3-methylazulen-1-yl)alkan-1-ones, when oxidized with excess 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (=4,5-dichloro-3,6-dioxocyclohexa-1,4- diene-1,2-dicarbonitrile; DDQ) in aqueous acetone in the presence of 1-(3-demethylazulen-1-yl)alkan-1-ones, form the corresponding unsymmetrically substituted bis(3-acylazulen-1-yl)methanones in good to excellent yields (Schemes 4, 5, 7, and 10). Intermediates are the corresponding disubstituted methane derivatives, which are formed by radical and radical-cation recombination (Scheme 6). The 1-(3-methylazulen-1-yl)alkan-1-ones can as well be coupled oxidatively with azulene itself, benz[a]azulene, or 1,3-dimethoxybenzene (Schemes 9 - 11).

Full text of DOI:10.1002/hlca.201000032

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A New Method for the Synthesis of Nonsymmetrically Substituted Bis(azulen-
1-yl) Ketones
by Rolf Sigrist and Hans-Jꢀrgen Hansen*
Organisch-chemisches Institut der Universitꢀt Zꢁrich, Winterthurerstrasse 190, CH-8057 Zꢁrich
(phone: þ 41-44-6354231; fax: þ 41-44-6359812; e-mail: H.-J.H@access.uzh.ch)
The 1-(3-methylazulen-1-yl)alkan-1-ones, when oxidized with excess 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (¼4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile; DDQ) in aqueous ace-
tone in the presence of 1-(3-demethylazulen-1-yl)alkan-1-ones, form the corresponding unsymmetrically
substituted bis(3-acylazulen-1-yl)methanones in good to excellent yields (Schemes 4, 5, 7, and 10).
Intermediates are the corresponding disubstituted methane derivatives, which are formed by radical and
radical-cation recombination (Scheme 6). The 1-(3-methylazulen-1-yl)alkan-1-ones can as well be
coupled oxidatively with azulene itself, benz[a]azulene, or 1,3-dimethoxybenzene (Schemes 9 – 11).
Introduction. – In the preceding communication, we reported on the oxidation of 1-
(3,8-dimethylazulen-1-yl)alkan-1-ones 1 with 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (¼4,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile; DDQ) in aque-
ous acetone [1]. Beside the azulene-1-carboxaldehydes 2, the expected products [2], we
isolated in small amounts the pentacyclic compounds 3 and their precursors 4 and, in
addition, the symmetrically substituted 1,1’-[(carbonylbis(8-methylazulene-3,1-diyl)]-
bis[alkan-1-ones] (¼ bis(3-acyl-4-methylazulen-1-yl)methanones) 5 (Scheme 1). The
observation that the formation of the latter compounds seemed to be dependent on the
appearance of the corresponding carboxylic acids of 2 in the reaction as well as the
possibility to base on this finding a general procedure for the synthesis of nonsym-
metrically substituted bis(azulen-1-yl)methanones motivated us to study the mecha-
nism of the formation of compounds of type 5 in more detail. We report in the following
on these studies.
Synthesis of Nonsymmetrically Substituted Bis(azulen-1-yl)methanones. – The
oxidation of 1a (R1 ¼ Me, R2 ¼ i-Pr; Scheme 1) in the presence of the corresponding
azulene-1-carboxylic acid 6a with DDQ in aqueous acetone gave the triketone 5a in a
yield of 26%, accompanied by 6% of its methane precursor 7a [1] (see Scheme 2 for the
corresponding labeled compounds). The combined yields of 5a and 7a of less than 50%
gave, therefore, no unequivocal information on the involvement of acid 6a in their
formation. So we repeated the experiment with the 13C-labeled acid 6a* and isolated
indeed the 13C-labeled triketone 5a* with almost half the percentage of label in the Ac
groups on grounds of symmetry (Scheme 2). This experiment demonstrated that
corresponding azulene-1-carboxylic acids are indeed precursors of the triketones, so
ꢂ 2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 93 (2010)
1569
Scheme 1
Scheme 2
1
)
Proof of presence by TLC, but not isolated.

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Helvetica Chimica Acta – Vol. 93 (2010)
that on this way, the synthesis of methanones with two different azulenyl residues is
possible.
However, a cross-experiment of oxidation with DDQ, acid 6a, and the (azulen-1-
yl)phenylmethanone 1b failed more or less since the nonsymmetrically substituted
methanone 5ab was isolated in a yield of only 12%, accompanied by ca. 1% of its
methane precursor 7ab (Scheme 3). Main product was the azulene-1-carboxaldehyde
2b, and also the symmetrically substituted triketone 5b was found in 6% yield.
Scheme 3
These results were not very encouraging, so we argued that the intermediate
azulene-1-carboxylic acids react too sluggishly with the 1-acylazulenyl-3-methyl2)
cations, and they may decarboxylate to the corresponding (azulen-1-yl)alkan-1-ones
before further reactions take place. Therefore, we treated 1-(5-isopropyl-3,8-dimethyl-
azulen-1-yl)ethanone (¼ 3-acetylguaiazulene; 1a) with its 3-demethyl compound 1c in
the presence of DDQ in aqueous acetone. The result was amazing since the
symmetrically substituted methanone 5a was now the main product (Scheme 4) and
the oxidized azulene-1-carboxaldehyde 2a was only present in trace amount. The yield
of methanone 5a could be increased to 80% by doubling the molar amount of DDQ.
Similar results were obtained on DDQ oxidation of 1b in the presence of twice the
molar amount of its 3-demethyl derivative 1d (Scheme 4). In this case, the symmetric
methanone 5b was obtained in a reasonable yield of 64%, beside small amounts of
azulene-1-carboxaldehyde 2b.
2
)
For convenience, the locant in the names of the type 1-acylazulen-3-methyl refers to the positions of
the acyl and Me groups in the starting azulene derivative.

Helvetica Chimica Acta – Vol. 93 (2010)
1571
Scheme 4
Scheme 5
These experimental results gave an excellent basis for the aimed synthesis of
nonsymmetrical bis(azulen-1-yl) ketones as displayed in Scheme 5. The observation
that the formation of the azulene-1-carboxaldehydes 2 is strongly reduced in the
3
)
)
)
)
First/second number, molar ratio of reactants 1:2:4/1:2:8.
Molar ratio of reactants 1:2:8.
First number, molar ratio of reactants 1:2:4; second number 1:4:4.
First yield for 1b þ 1c; second yield for 1a þ 1d; molar ratio of reactants in both cases 1:2:8.
4
5
6

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presence of the 3-demethylazulenes 1c – 1e in aqueous acetone speaks for the fact that
the generation of (3-acylazulen-1-yl)methyl cations are not involved in the formation
of the bis(azulen-1-yl) ketones as we have postulated in the preceding report [1].
We assume, therefore, that the ketone formation is based on the recombination of
azulene radical cations and azulen-1-ylmethyl radicals as depicted in Scheme 6 for the
oxidative coupling of 1b with 1e. Crucial intermediates are the corresponding
bis(azulenyl)methanes 7, which are then oxidized by DDQ to the bis(azulen-1-
yl)methanones 57). The global reaction ending with the formation of 5 needs,
therefore, at minimum two moles of DDQ.
Scheme 6
In view of further evidence for the proposed coupling mechanism, we treated 1-
(azulen-1-yl)ethanone (1g) under our standard conditions with 1-(5-isopropyl-3,8-
dimethylazulen-1-yl)ethanone (1a). In this case, we obtained an almost 1:1 mixture of
2a and the expected triketone 5ag (Scheme 7). The 1-(4,6,8-trimethylazulen-1-
yl)ethanone (1h) as well as the methyl 4,6,8-trimethylazulene-1-carboxylate (1i), on
7
)
We checked the general ease of this DDQ oxidation in acetone/H2O 9:1 only in the case of 7f,
which was separately prepared as shown below:

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1573
Scheme 7
the other hand, turned out to be excellent partners for the oxidative coupling with 1a
under the standard conditions (Scheme 7).
These results are in agreement with the assumption that the formation of azulene
.
radical cations of type 1eþ by reaction with DDQ (Scheme 6) is easier for 1h and 1i
than for 1g due to the Me groups at the seven-membered ring of 1h and 1i9). The
oxidative coupling of 1a and 1i was optimized with respect to a maximum yield of 5ai,
which was attained with a 2 :1:8 molar ratio of the reactants. It was also of interest that
we could isolate in this case the normal oxidation product 2a of 1a in a yield of 35%
with respect to the 100% surplus of 1a in view of the coupling process.
It has already been found by Okajima and Kurokawa [2] that 2,2,2-trifluoro-1-(5-
isopropyl-3,8-dimethylazulen-1-yl)ethanone (¼ 3-(trifluoroacetyl)guaiazulene; 1j) un-
dergoes the oxidation with DDQ only very sluggishly, so that they obtained the
azulenecarboxaldehyde 2j solely in a yield of 29%. Therefore, it was of interest for us to
look how 1j would behave in the presence of the effective coupling partner 1h. The
results of this test reaction under our standard condition (reactant ratio 1:2 :4, 20 min,
r.t., acetone/H2O 9 :1) are displayed in Scheme 8.
The specific behavior of 1j is understandable. The strong electron-acceptor
substituent at C(1) makes the first one-electron oxidation by DDQ more difficult,
which also should be true for the second one after proton loss of the formed radical
8
)
)
Trace amounts of the symmetric triketone 5a were also found.
See [3] for EPR and ENDOR measurements of radical cations of alkylazulenes.
9

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Scheme 8
cation. It seems that there is no good matching of the production rate of the azulen-1-
ylmethyl radicals of 1j and that of the radical cation of 1h. The yield of the coupling
product 5hj is thus low in comparison with the 86% of 5ah of the oxidative coupling of
1a with 1h under the same conditions (cf. Scheme 7). Nevertheless, the sum of the
absolute yields of 2j and 5hj, which reflects the formation of azulen-1-ylmethyl radicals
from 1j, is slightly higher than the yield reported for the formation of 2j [2].
To establish that the oxidative coupling reaction of 1-(3-methylazulen-1-yl)alkan-1-
ones and 1-(azulen-1-yl)alkan-1-ones is not bound to the presence of an acyl group at
the latter, we oxidized 1a with a large molar excess of DDQ in the presence of azulene
(8) itself and with a longer exposure time to DDQ. Indeed, we isolated, beside 2a,
triketone 5a, as products of 1a, small amounts of the expected diketone 9 and, to our
surprise, slightly larger amounts of the symmetric tetraketone 10, built of 8 as central
unit and two units of 1a in 1,3-position of 8 (Scheme 9). To suppress the dominant
formation of 2a, a second 30 min run was performed in the presence of a fivefold molar
amount of 8 with respect to 1a under otherwise the usual reaction conditions. This time,
we found only 9, but again in small yield. The observation that we found in the first run
roughly twice as much tetraketone 10 as diketone 9 could mean that indeed the first
alkylation step 8 ! methane intermediate, followed by DDQ oxidation to 9 (cf.
Scheme 6), is more reluctant than the second alkylation step 9 ! methane intermedi-
ate, followed by DDQ oxidation to 10. In other words, an acyl group at C(1) of an
azulene favors the oxidative coupling reaction with DDQ in aqueous acetone.
Therefore, we oxidized 1a in the presence of a fivefold molar amount of 8 and with a
high excess of DDQ (Scheme 9). In this case, we found only 9 in isolable amounts, but
again in low yield. These results together with those of the oxidation of 1a in the
presence of 1-(azulen-1-yl)ethanone (1g; see Scheme 7) clearly demonstrated that an
acyl group at C(1) of an azulene favors its oxidative coupling with a 1-(3-methylazulen-
1-yl)alkan-1-one by DDQ. As consequence of this finding, we treated finally 1a and
diketone 9 with a large excess of DDQ. The outcome of this oxidation is displayed in
Scheme 10. Now, beside larger amounts of 2a, the tetraketone 10 was the main product,
which was obtained in pure state in a yield of 54%.
10
)
)
Recovered 1j after reaction.
First number absolute yield, second number yield with respect to recovered 1j.
11

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1575
Scheme 9
Scheme 10

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Helvetica Chimica Acta – Vol. 93 (2010)
´
´
The resume of the oxidative coupling reactions of the azulenes, so far investigated,
is that alkyl substituents at the seven-membered ring and acyl or alkoxycarbonyl groups
at C(1) of the five-membered ring favor the coupling reaction, whereby the Me group at
C(3) becomes the later central C¼O group in the coupling products. Both azulene
reactants should have similarly high-lying HMO, so that their SET reaction with DDQ
produces the corresponding radical cations with almost the same rate to get high yields
of coupling products. The presence of H2O in the solvent mixture is obligatory for the
oxidative formation of the central C¼O group. Moreover, H2O is also an indicator for
the appearance of azulen-1-ylmethyl cations, which are trapped by H2O and then
further oxidized by DDQ to azulene-1-carboxaldehydes. This will happen always in
cases where the production rate of azulene radical cations of the reaction partner is too
low, so that the azulen-1-ylmethyl radical can couple only to a small extent with radical
cations leading after proton loss to the intermediate bis(azulen-1-yl)methanes. In a
more general perspective, one would, therefore, expect that 1-(3-methylazulen-1-
yl)alkan-1-ones can be coupled with any substrate provided that its HMO are
energetically close to those of the azulene.
We tested this idea by reacting our reference azulene 1a with benz[a]azulene (11)
[4] under the usual conditions for an oxidative coupling reaction driven by DDQ
(Scheme 11). Indeed, we found, beside 2a (29%), the new diketone 12 in a good yield.
More interesting was the fact that the repetition of this oxidative coupling, however,
Scheme 11
12
)
At best trace amounts.

Helvetica Chimica Acta – Vol. 93 (2010)
1577
with the difference that we ran the reaction during the first minute in pure acetone and
added then H2O to get the 9 :1 solvent mixture, led to almost pure 12, accompanied at
best by traces of 2a. These results mean that in the present case, the reactants have
been oxidatively consumed within the very first minute after mixing. The disubstituted
methane intermediate is then further oxidized to 12 after addition of H2O. That the
radical-cation formation from 11 and radical production from 1a is in this case not fully
balanced, demonstrates the experiment in aqueous acetone, where also the azulene-1-
carboxaldehyde 2a is formed without touching the yield of 12.
Finally, we chose 1,3-dimethoxybenzene (13) as partner for the DDQ-mediated
oxidative coupling with 1a. The first experiment under the usual conditions and with a
molar ratio 1:2 :8 of the reactants was disappointing since no coupling products at all
were formed. However, when we proceeded as in the case of 1a and 11, i.e., reaction
first in pure acetone, followed by later addition of H2O, and with 13 in a tenfold molar
amount with respect to 1a, we found 24% of the desired coupling product 14,
accompanied by small amounts of 2a and 5a (Scheme 11).
We are thankful to Christoph Oberli and Petra Wolint for experimental assistance, to our NMR
laboratory for specific NMR measurements, our MS laboratory for mass spectra, and our laboratory for
microanalysis for elemental analyses. Financial support of this work by the Swiss National Science
Foundation is gratefully acknowledged.
Experimental Part
General. See [1]. TLC: Silica gel (SiO2) coated aluminium sheets, if not otherwise stated. General
procedure: see 2.4.
1. DDQ Oxidation of 1-(3-Methylazulen-1-yl)alkan-1-ones in the Presence of Azulene-1-carboxylic
Acid 6a. The reactions were performed as described in [1]. 1.1. 1-(5-Isopropyl-3,8-dimethylazulen-1-
yl)ethanone (1a) in the Presence of 6a*13) (cf. Scheme 2). Products 2a, 5a*, and 7a*. (3-[13C2]Acetyl-5-
isopropyl-8-methylazulen-1-yl)(3-acetyl-5-isopropyl-8-methylazulen-1-yl)methanone (¼1-{3-[(3-Acetyl-
7-isopropyl-4-methylazulen-1-yl)carbonyl]-5-isopropyl-8-methylazulen-1-yl}[1,2-13C2]ethanone; 5a*):
See compound 4a in [1]. 1H-NMR (300 MHz, CDCl3): 2.91 and 2.89, 2.48 and 2.46 (dd, 1J(H,13C) ¼
13
127.3, 2J(H,13C) ¼ 5.7, 13CH3ꢀ C¼O); 2.69 (s, MeꢀC¼O). 13C-NMR (75 MHz, CDCl3): 197.11 and
13
13
196.54 (d, 1J(O¼13Cꢀ CH3) ¼ 42.6, 13CH3ꢀ C¼O); 196.83 (s, MeꢀC¼O); 30.49 and 29.93 (d,
1J(O¼13Cꢀ CH3) ¼ 42.6, 13CH3ꢀ C¼O); 30.22 (MeꢀC¼O). CI-MS (C33H34O3 (478.63)): 481.2 (53,
[M þ 3]þ), 479.2 (100, [M þ 1]þ).
13
13
1.2. 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)phenylmethanone (1b) in the Presence of 6a (cf.
Scheme 3). Products 2b, 5ab, 7ab, 5b, and 7b. (3-Acetyl-7-isopropyl-4-methylazulen-1-yl)(3-benzoyl-7-
isopropyl-4-methylazulen-1-yl)methanone (¼1-{3-[(3-Benzoyl-7-isopropyl-4-methylazulen-1-yl)carbon-
yl]-5-isopropyl-8-methylazulen-1-yl}ethanone; 5ab). Red glassy powder. M.p. 109 – 1138. Rf (toluene/
t-BuOMe 6 :1) 0.40. IR (CHCl3): 3059vw, 2966w, 2931w, 2871w, 1651m, 1598w, 1580w, 1505m, 1443m,
1408s, 1386w, 1371w, 1303w, 1164w, 994w, 960w, 947w, 900w, 876w, 851w, 828w, 817w. 1H-NMR (300 MHz,
CDCl3): 9.84, 9.80 (2d, 4J(6,8) ¼ J(6’,8’) ¼ 2.1, HꢀC(8,8’)); 8.32 (s, HꢀC(2)); 8.06 (s, HꢀC(2’)); 7.98 (dd
with f.s., Jo ꢁ 8.2, Jm ꢁ 1.5, Ho of Ph); 7.86, 7.78 (2dd, 3J(5,6) ¼ J(5’,6’) ¼ 10.9, 4J(6,8) ¼ J(6’,8’) ¼ 2.1,
HꢀC(6,6’)); 7.63, 7.62 (2d, 3J(5,6) ¼ J(5’,6’) ¼ 10.9, HꢀC(5,5’)); 7.55 (tt, Jo ꢁ 7.4, Jm ꢁ 1.3, Hp of Ph); 7.44 (t
with f.s., Jo ꢁ 7.5, Hm of Ph); 3.28 (sept., J ¼ 6.9, Me2CHꢀC(7’)); 3.23 (sept., J ¼ 6.9, Me2CHꢀC(7));
2.91 (s, MeꢀC(4)); 2.88 (s, MeꢀC(4’)); 2.66 (s, MeCOꢀC(3)); 1.43 (d, J ¼ 6.9, Me2CHꢀC(7’)); 1.39 (d,
The acid 6a* with a [13C2]Ac group (25 atom-% 13C) was obtained by oxidation of the
correspondingly labeled azulene-1-carboxaldehyde 2a* with KMnO4 in the presence of Na2CO3
in acetone/water 9:1 (cf. [1]).
13
)

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Helvetica Chimica Acta – Vol. 93 (2010)
J ¼ 6.9, Me2CHꢀC(7)). 13C-NMR (75 MHz, CDCl3): 196.62 (MeCOꢀC(3)); 194.38 (PhCOꢀC(3’));
189.11 (C¼O); 151.45 – 126.30 (20 azulene C)14); 38.48 Me2CHꢀC(7’)); 38.36 (Me2CHꢀC(7)); 30.21
(MeCOꢀC(3)); 29.07 (MeꢀC(4)); 28.77 (MeꢀC(4’)); 24.45 (Me2CHꢀC(7’)); 24.37 (Me2CHꢀC(7)).
CI-MS (NH3): 541 (100, [M þ H]þ). Anal. calc. for C38H36O3 (540.70): C 84.41, H 6.71; found: C 84.25, H
6.80.
Bis(3-benzoyl-7-isopropyl-4-methylazulen-1-yl)methanone (5b): See compound 4e in [1].
2. DDQ Oxidation of 1-(3-Methylazulen-1-yl)alkan-1-ones in the Presence of 1-(3-demethylazulen-
1-yl)alkan-1-ones or Methyl 3-Demethylazulene-1-carboxylate. 2.1. 1-(5-Isopropyl-3,8-dimethylazulen-1-
yl)ethanone (1a) and 1-(5-Isopropyl-8-methylazulen-1-yl)ethanone (1c) (cf. Scheme 4). Products 2a and
5a. Data of 5a: See 4a in [1].
2.2. 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)ethanone (1a) and 1-(5-Isopropyl-8-methylazulen-1-
yl)phenylmethanone (1d) (cf. Scheme 5). Products 2a and 5ab. Data of 5ab: See 1.2.
2.3. 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)ethanone (1a) and 1-Azulen-1-yl)ethanone (1g) (cf.
Scheme 7). Products 2a and 5ag. (3-Acetylazulen-1-yl)(3-acetyl-7-isopropyl-4-methylazulen-1-yl)metha-
none (¼1-{3-[(3-Acetylazulen-1-yl)carbonyl]-5-isopropyl-8-methylazulen-1-yl}ethanone; 5ag). Dark red
crystals. M.p. 211 – 2138 (EtOH). Rf (hexane/AcOEt 1:1) 0.27. IR (KBr): 1651m, 1640m, 1585w.
1H-NMR (300 MHz, CDCl3): 10.10 (dd, 3J(4,5) ¼ 9.9, 4J(4,6) ¼ 0.8, HꢀC(4)); 9.85 (d, 4J(6’,8’) ¼ 2.1,
3
4
HꢀC(8’)); 9.72 (dd, J(7,8) ¼ 9.9, J(6,8) ¼ 0.8, HꢀC(8)); 8.55 (s, HꢀC(2)); 8.35 (s, HꢀC(2’)); 8.04 (t-
3
3
like, J(5,6) ꢁ J(6,7) ¼ 9.7, HꢀC(6)); 7.88 – 7.77 (superimp. signals of Hꢀ(5), HꢀC(6’), HꢀC(7)); 7.69
(d, 3J(5’,6’) ¼ 10.9, HꢀC(5’)); 3.23 (sept., J ¼ 6.9, Me2CHꢀC(7’)); 2.97 (s, MeꢀC(4’)); 2.70 (s,
MeCOꢀC(3)); 2.68 (s, MeCOꢀC(3’)); 1.41 (d, J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3):
196.95 (MeCOꢀC(3’)); 195.57 (MeCOꢀC(3)); 188.94 (C¼O); 151.65 – 123.66 (20 azulene C); 38.37
(Me2CHꢀC(7’)); 30.37 (MeCOꢀC(3)); 29.10 (MeCOꢀC(3’)); 24.35 (Me2CHꢀC(7’)). CI-MS (NH3):
423 (100, [M þ 1]þ), 310 (6), 309 (24), 290 (30), 200 (16). Anal. calc. for C29H26O3 (422.52): C 82.44, H
6.20; found: C 82.30, H 6.25.
2.4. 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)ethanone (1a) and 1-(4,6,8-Trimethylazulen-1-yl)etha-
none (1h) (cf. Scheme 7). The reactants 1a (0.048 g, 0.20 mmol) [1] and 1h (0.085 g, 0.40 mmol) [5] were
dissolved in acetone (9 ml), followed by gradual addition of H2O (1 ml), and then DDQ (0.181 g,
0.80 mmol) was added. The mixture was stirred during 20 min at r.t., and just thereafter subjected to a
first purification (method A [1], dioxane). The product separation was realized with method B (hexane/
AcOEt) [1]. The first fraction contained 1h (0.015 g, 35% of the excess). The second one delivered a
small amount of carboxaldehyde 2a (0.001 g, 2%) [1]. The third, red fraction gave the coupling product
(3-acetyl-7-isopropyl-4-methylazulen-1-yl)(3-acetyl-4,6,8-trimethylazulen-1-yl)methanone (¼1-{3-[(3-
acetyl-7-isopropyl-4-methylazulen-1-yl)carbonyl]-4,6,8-trimethylazulen-1-yl}ethanone; 5ah; 0.080 g,
86%). Red crystals. M.p. 196 – 1978 (EtOH). Rf (hexane/AcOEt 3 :1) 0.06. IR (KBr): 3096vw, 2962w,
2927w, 2867w, 1661s, 1606m, 1584m, 1548w, 1505m, 1436s, 1401s, 1368s, 1310w, 1221w, 1190s, 1159w,
1103w, 1028w, 955w, 915w, 881m, 853w, 795w, 731w. 1H-NMR (300 MHz, CDCl3): 10.06 (d, 4J(6’,8’) ¼ 2.1,
HꢀC(8’)); 8.22 (s, HꢀC(2’)); 8.01 (s, HꢀC(2)); 7.83 (dd, 3J(5’,6’) ¼ 10.9, 4J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.69 (d,
3J(5’,6’) ¼ 10.9, HꢀC(5’)); 7.43, 7.36 (2s, HꢀC(5), HꢀC(7)); 3.23 (sept., J ¼ 6.9, Me2CHꢀC(7’)); 2.93 (s,
MeꢀC(4’)); 2.91, 2.83, 2.69 (3s, MeꢀC(4), MeꢀC(6), MeꢀC(8)); 2.66 (s, MeCOꢀC(3’)); 2.61 (s,
MeCOꢀC(3)); 1.38 (d, J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3): 197.51 (MeCOꢀC(3));
197.27 (MeCOꢀC(3’)); 191.72 (C¼O); 152.24 – 125.27 (20 azulene C); 38.37 (Me2CHꢀC(7’)); 30.31
(MeꢀC(4’)); 29.92 (MeꢀC(4), MeꢀC(8)); 29.22 (MeCOꢀC(3)); 29.06 (MeCOꢀC(3’)); 28.14
(MeꢀC(6)); 24.34 (Me2CHꢀC(7’)). CI-MS (NH3): 465 (100, [M þ H]þ), 451 (12), 423 (8). Anal. calc.
for C32H32O3 (464.60): C 82.73, H 6.94; found: C 82.54, H 6.89.
2.5. 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)ethanone (1a) and Methyl 4,6,8-Trimethylazulene-1-
carboxylate (1i) (cf. Scheme 7). Products 2a and 5ai. Methyl 3-[(3-Acetyl-7-isopropyl-4-methylazulen-
1-yl)carbonyl]-4,6,8-trimethylazulene-1-carboxlate (5ai). Red crystals. M.p. 206 – 2088 (EtOH). Rf
(hexane/AcOEt 2 :1) 0.16. IR (KBr): 3091vw, 2958w, 2930w, 2868w, 1704m (COOMe), 1662m (MeCO),
1606m (C¼O), 1582m, 1549w, 1506m, 1439s, 1402s, 1369s, 1313w, 1214m, 1193s, 1159m, 1106w, 1053w,
Here and in the following part, only the position of the 13C-core signals at lowest and highest field of
the azulene moieties are given.
14
)

Helvetica Chimica Acta – Vol. 93 (2010)
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1026w, 994w, 956w, 881m, 854w, 782w, 772m. 1H-NMR (300 MHz, CDCl3): 10.02 (d, 4J(6’,8’) ¼ 2.1,
HꢀC(8’)); 8.25 (s, HꢀC(2’)); 8.02 (s, HꢀC(2)); 7.81 (dd, 3J(5’,6’) ¼ 10.9, 4J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.67 (d,
3J(5’,6’) ¼ 10.9, HꢀC(5’)); 7.40, 7.34 (2s, HꢀC(5), HꢀC(7)); 3.88 (s, MeOCOꢀC(1)); 3.22 (sept., J ¼ 6.9,
Me2CHꢀC(7’)); 3.00, 2.92, 2.85, 2.68 (4s, MeꢀC(4), MeꢀC(6), MeꢀC(8), MeꢀC(4’)); 2.62 (s,
MeCOꢀC(3’)); 1.38 (d, J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3): 197.36 (MeCOꢀC(3’));
191.55 (C¼O); 167.78 (MeOCOꢀC(1)); 152.09 – 118.79 (20 azulene C); 51.93 (MeOCOꢀC(1)); 38.37
(Me2CHꢀC(7’)); 30.44 (MeꢀC(4’)); 29.06 (MeCOꢀC(3’)); 29.31, 28.85, 28.20 (MeꢀC(4), MeꢀC(6),
.
MeꢀC(8)); 24.36 (Me2CHꢀC(7’)). EI-MS: 480 (38, Mþ ), 465 (98), 437 (100). Anal. calc. for C32H32O4
(480.60): C 79.97, H 6.71; found: C 80.01, H 6.73.
2.6. 5-Isopropyl-3,8-dimethylazulen-1-yl)phenylmethanone (1b) and 1-(5-Isopropyl-8-methylazulen-
1-yl)ethanone (1c) (cf. Scheme 5). Products 2b and 5ab. Data of 5ab: See 1.2.
2.7. (5-Isopropyl-3,8-dimethylazulen-1-yl)phenylmethanone (1b) and (5-Isopropyl-8-methylazulen-1-
yl)phenylmethanone (1d) (cf. Scheme 4). Products 2b and 5b. Data of 5b: See compound 4e in [1].
2.8. (5-Isopropyl-3,8-dimethylazulen-1-yl)phenylmethanone (1b) and 1-(7-Isopropyl-4-methylazu-
len-1-yl)ethanone (1e) (cf. Scheme 5). Products 2b and 5be. (3-Acetyl-5-isopropyl-8-methylazulen-1-
yl)(3-benzoyl-7-isopropyl-4-methylazulen-1-yl)methanone (¼1-{3-[(3-Benzoyl-7-isopropyl-4-methyla-
zulen-1-yl)carbonyl]-7-isopropyl-4-methylazulen-1-yl}ethanone; 5be). Dark red crystals. M.p. 210 –
2128 (octane). Rf (hexane/AcOEt 1:1) 0.39. IR (KBr): 2962m, 1639s, 1615m, 1598m. 1H-NMR
(300 MHz, C6D6): 10.76 (d, 4J(4,6) ¼ 2.1, HꢀC(4)); 10.58 (d, 4J(6’,8’) ¼ 2.1, HꢀC(8’)); 8.23 (s, HꢀC(2));
3
4
8.18 (s, HꢀC(2’)); 8.02 (d with f.s., Jo ¼ 8, Ho of Ph); 7.23 (dd, J(5’,6’) ¼ 10.8, J(6’,8’) ¼ 2.1, HꢀC(6’));
3
7.16 – 6.99 (overlapping signals of Hp, Hm, HꢀC(6), HꢀC(7)); 6.93 (d, J(5’,6’) ¼ 10.8, HꢀC(5’)); 2.92
(sept., J ¼ 6.9, Me2CHꢀC(7’)); 2.88 (s, MeꢀC(8)); 2.84 (sept., J ¼ 6.9, Me2CHꢀC(5)); 2.79 (s,
MeꢀC(4’)); 2.35 (s, MeCOꢀC(3)); 1.23 (d, J ¼ 6.9, Me2CHꢀC(7’)); 1.18 (d, J ¼ 6.9, Me2CHꢀC(5)).
13C-NMR (75 MHz, CDCl3): 195.18 (MeCOꢀC(3)); 194.29 (PhCOꢀC(3’)); 191.33 (C¼O); 151.80 –
122.23 (20 azulene C); 38.40, 38.36 (Me2CHꢀC(5), Me2CHꢀC(7’)); 29.04 (MeCOꢀC(3)); 28.65
(MeꢀC(4’)); 28.31 (MeꢀC(8)); 24.41, 24.38 (Me2CHꢀC(5), Me2CHꢀC(7’)). CI-MS: 541 (100, [M þ
1]þ). Anal. calc. for C38H36O3 (540.70): C 84.41, H 6.71; found: C 84.25, H 6.65.
2.9. 2,2,2-Trifluoro-1-(5-isopropyl-3,8-dimethylazulen-1-yl)ethanone (1j) and 1-(4,6,8-Trimethyl-
azulen-1-yl)ethanone (1h) (cf. Scheme 8). Products 2j and 5hj. (3-Acetyl-4,6,8-trimethylazulen-1-yl)[7-
isopropyl-4-methyl-3-(trifluoroacetyl)azulen-1-yl]methanone (¼1-{3-[(3-Acetyl-4,6,8-trimethylazulen-1-
yl)carbonyl]-5-isopropyl-8-methylazulen-1-yl}-2,2,2-trifluoroethanone; 5hj). Red crystals. M.p. 175 – 1778
(EtOH). Rf (hexane/AcOEt 2 :1) 0.29. IR (KBr): 2966w, 2931w, 2873w, 1666s, 1610m, 1583m, 1547w,
1511s, 1434m, 1410s, 1365s, 1311w, 1280m, 1200m, 1168s, 1133s, 1107w, 1078m, 1031w, 950m, 923w, 844s,
795w, 733w, 716w. 1H-NMR (300 MHz, CDCl3): 10.16 (d, 4J(6’,8’) ¼ 2.1, HꢀC(8’)); 8.50 (q, 5J(F,2’) ¼ 2.1,
3
4
3
HꢀC(2’)); 8.06 (s, HꢀC(2)); 7.97 (dd, J(5’,6’) ¼ 10.9, J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.86 (d, J(5’,6’) ¼ 10.9,
HꢀC(5’)); 7.48, 7.42 (2s, HꢀC(5), HꢀC(7)); 3.29 (sept., J ¼ 6.9, Me2CHꢀC(7’)); 2.97 (s, MeꢀC(4’));
2.92, 2.85, 2.69 (3s, MeꢀC(4), MeꢀC(6), MeꢀC(8)); 2.65 (s, MeCOꢀC(3)); 1.42 (d, J ¼ 6.9,
Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3): 197.06 (MeCOꢀC(3)); 190.71 (C¼O); 176.55 (q,
2J(13C,F) ¼ 33.9, CF3COꢀC(3’)); 154.99 – 118.69 (20 azulene C); 117.33 (q, 1J(13C,F) ¼ 292.3,
CF3COꢀC(3’)); 38.59 (Me2CHꢀC(7’)); 30.14 (MeꢀC(4’)); 29.98, 29.55, 29.23 (3s, MeꢀC(4), MeꢀC(6),
.
MeꢀC(8)); 28.12 (MeCOꢀC(3)); 24.34 (Me2CHꢀC(7’)); EI-MS: 518 (46, Mþ ), 503 (100, [M ꢀ Me]þ),
.
475 (19, [M ꢀ CO]þ ), 421 (40, [M ꢀ CF3CO]þ), 307 (17), 281 (30), 197 (61). Anal. calc. for C32H29F3O3
(518.58): C 74.12, H 5.64; found: C 73.69, H 5.45.
3. DDQ Oxidation of 1-(5-Isopropyl-3,8-dimethylazulen-1-yl)ethanone (1a) in the Presence of
Azulenes and 1,3-Dimethoxybenzene. – 3.1. With Azulene (8) (cf. Scheme 9). Products 2a, 5a, 9, and 10.
(3-Acetyl-7-isopropyl-4-methylazulen-1-yl)(azulen-1-yl)methanone (¼1-[3-(Azulen-1-ylcarbonyl)-5-iso-
propyl-8-methylazulen-1-yl]ethanone; 9). Red crystals. M.p. 152 – 1548 (EtOH). Rf (toluene/t-BuOMe
6 :1) 0.32. IR (KBr): 2962w, 2928w, 2872w, 1648m, 1586m, 1534w, 1506m, 1495m, 1456m, 1417s, 1407s,
1396s, 1370m, 1315w, 1285w, 1221w, 1202m, 1191m, 1143w, 1051w, 1020w, 954w, 890w, 788m, 777m, 751w.
4
1H-NMR (300 MHz, CDCl3): 9.80 (d, J(6’,8’) ¼ 2.1, HꢀC(8’)); 9.64 (d,3J(7,8) ¼ 9.7, HꢀC(8)); 8.54 (d,
3
3J(4,5) ¼ 9.2, HꢀC(4)); 8.37 (s, HꢀC(2’)); 8.18 (d, 3J(2,3) ¼ 4.1, HꢀC(2)); 7.85 (t, 3J(5,6) ꢁ J(6,7) ¼ 9.7,
HꢀC(6)); 7.80 (dd, 3J(5’,6’) ¼ 10.9, 4J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.64 (d, 3J(5’,6’) ¼ 11.1, HꢀC(5’)); 7.58, 7.49
(2t, 3J ¼ 9.9, resp. 9.6, HꢀC(5), HꢀC(7)); 7.37 (d, 3J(2,3) ¼ 4.1, HꢀC(3)); 3.21 (sept., J ¼ 6.9,

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Helvetica Chimica Acta – Vol. 93 (2010)
Me2CHꢀC(7’)); 2.95 (s, MeꢀC(4’)); 2.70 (s, MeCOꢀ(3’)); 1.39 (d, J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR
(75 MHz, CDCl3): 197.00 (MeCOꢀC(3’)); 189.15 (CO); 151.19 – 117.47 (20 azulene C); 38.33
(Me2CHꢀC(7’)); 30.35 (MeCOꢀC(3’)); 29.05 (MeꢀC(4’)); 24.34 (Me2CHꢀC(7’)). CI-MS (NH3):
381 (100, [M þ H]þ). Anal. calc. for C27H24O2 (380.49): C 85.23, H 6.36; found: C 85.13, H 6.52.
1,3-Bis[(3-acetyl-7-isopropyl-4-methylazulen-1-yl)carbonyl]azulene (¼1,1’-{Azulene-1,3-diylbis[car-
bonyl(5-isopropyl-8-methylazulene-3,1-diyl)]}bis[ethanone]; 10). Red crystals. M.p. 264 – 2658 (EtOH/
AcOEt 3 :1). Rf (hexane/AcOEt 1:1) 0.16. IR (KBr): 3053vw, 2962m, 2928w, 2869w, 1661m, 1618m,
1589m, 1505s, 1441s, 1418s, 1387m, 1370m, 1298w, 1218m, 1195s, 1164m, 960w, 938w, 899w, 889w, 870w,
783m, 769w, 756w, 608w. 1H-NMR (300 MHz, CDCl3): 9.89 (d, 4J(6’,8’) ¼ 2.1, HꢀC(8’)); 9.74 (d,
3J(4,5) ¼ 3J(7,8) ¼ 9.8, HꢀC(4), HꢀC(8)); 8.34 (s, HꢀC(2)); 8.25 (s, HꢀC(2’)); 8.05 (t, 3J(5,6) ¼
3
3
3J(6,7) ¼ 9.7, HꢀC(6)); 7.81 (dd, J(5’,6’) ¼ 10.9, 4J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.80 (t, J(4,5) ¼ 3J(7,8) ꢁ 10.0,
HꢀC(5), HꢀC(7)); 7.63 (d, 3J(5’,6’) ¼ 10.9, HꢀC(5’)); 3.24 (sept., 3J ¼ 6.9, Me2CHꢀC(7’)); 2.89 (s,
MeꢀC(4’)); 2.57 (s, MeCOꢀC(3’)); 1.42 (d, 3J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3):
197.25 (MeCOꢀC(3’)); 189.44 (COꢀC(1), COꢀC(3)); 151.49 – 125.75 (30 azulene C; signal ratio 1:2);
38.44 (Me2CHꢀC(7’)); 30.50 (MeCOꢀC(3’)); 29.05 (2 MeꢀC(4’)); 24.40 (Me2CHꢀC(7’)). ESI-MS
(NaI): 655 (100, [M þ Na]þ). Anal. calc. for C44H40O4 (632.80): C 83.52, H 6.37; found: C 83.57, H 6.39.
3.2. With (3-Acetyl-7-isopropyl-4-methylazulen-1-yl)(azulen-1-yl)methanone (9) (cf. Scheme 10).
Products 2a, 5a, and 10. Data of 10: See 3.1.
3.3. With Benz[a]azulene (11) (cf. Scheme 11). Products 2a and 12.
(3-Acetyl-7-isopropyl-4-methylazulen-1-yl)(benz[a]azulen-10-yl)methanone (¼1-[3-(Benz[a]azu-
len-10-ylcarbonyl)-5-isopropyl-8-methyl]ethanone; 12). Red crystals. M.p. 152 – 1548 (amorphous). Rf
(toluene/t-BuOMe 20 :1) 0.23. IR (KBr): 3050w, 2962w, 2927w, 2868w, 1662m, 1601m, 1555w, 1518m,
1505m, 1478m, 1451s, 1411s, 1371m, 1312w, 1263w, 1248w, 1191m, 1160w, 1139w, 1078w, 957w, 927w, 876w,
788w, 760w, 731w, 690w. 1H-NMR (600 MHz, CDCl3): 9.93 (d, 4J(6’,8’) ¼ 2.1, HꢀC(8’)); 8.71 (dd,
4
3
3
3J(5,6) ¼ 8.6, J(5,7) ¼ 0.9, HꢀC(5)); 8.66 (d, J(8,9) ¼ 11.1, HꢀC(9)); 8.47 (d, J(3,4) ¼ 7.9, HꢀC(4));
8.25 (s, HꢀC(2’)); 7.84 (d, 3J(1,2) ¼ 8.0, HꢀC(1)); 7.80 (dd, 3J(5’,6’) ¼ 11.0, 4J(6’,8’) ¼ 2.1, HꢀC(6’)); 7.66
(d, 3J(5’,6’) ¼ 11.0, HꢀC(5’)); 7.60 (ddd, 3J(1,2) ¼ 8.0, 3J(2,3) ¼ 7.0, 4J(2,4) ¼ 1.0, HꢀC(2)); 7.52 (ddd,
3J(3,4) ¼ 8.0, 3J(2,3) ¼ 7.0, 4J(1,3) ¼ 0.9, HꢀC(3)); 7.49 (br. ddt, 3J(6,7) ¼ 10.9, 3J(7,8) ¼ 8.6, 4J(5,7) ꢁ
4J(7,9) ꢁ 1.0, HꢀC(7)); 7.38 (br. dd, 3J(6,7) ¼ 10.9, 3J(5,6) ¼ 8.6, HꢀC(6)); 7.14 (ddd, 3J(8,9) ¼ 11.1,
3J(7,8) ¼ 8.6, 4J(6,8) ¼ 0.7, HꢀC(8)); 3.19 (sept., J ¼ 6.9, Me2CHꢀC(7’)); 2.95 (s, MeꢀC(4’)); 2.50 (s,
MeCOꢀC(3’)); 1.35 (d, J ¼ 6.9, Me2CHꢀC(7’)). 13C-NMR (75 MHz, CDCl3): 197.10 (MeCOꢀC(3’));
189.74 (COꢀC(10)); 151.60 – 120.84 (20 azulene C, 4 benzo C); 38.33 (Me2CHꢀC(7’)); 30.25
.
(MeCOꢀC(3’)); 29.09 (MeꢀC(4’)); 24.26 (Me2CHꢀC(7’)). EI-MS: 430 (100, Mþ ), 415 (55, [M ꢀ
.
Me]þ), 402 (37, [M ꢀ CO]þ ), 387 (93, [M ꢀ MeCO]þ). Anal. calc. for C31H26O2 (430.54): C 86.48, H
6.09; found: C 86.45, H 6.21.
3.4. With 1,3-Dimethoxybenzene (13) (cf. Scheme 11). Products 2a, 5a, and 14. (3-Acetyl-7-isopropyl-
4-methylazulen-1-yl)(2,4-dimethoxyphenyl)methanone (¼1-[3-(2,4-Dimethoxybenzoyl)-5-isopropyl-8-
methylazulen-1-yl]ethanone; 14). Red crystals. M.p. 108 – 1098 (EtOH). Rf (t-BuOMe/hexane 2 :1)
0.26. IR (KBr): 3073vw, 2963m, 2869w, 2840w, 1655s, 1614s, 1579m, 1504s, 1445s, 1407s, 1371m, 1360s,
1308m, 1290m, 1265s, 1245m, 1209s, 1183s, 1159s, 1139m, 1100w, 1041m, 1029m, 984w, 962m, 925m, 905w,
888m, 828m, 793m, 616m, 608w, 573w. 1H-NMR (300 MHz, C6D6): 10.58 (br. s, HꢀC(8)); 8.27 (s,
HꢀC(2)); 7.60 (d, 3J(5’,6’) ¼ 8.4, HꢀC(6’)); 7.20 (br. d, 3J(5,6) ¼ 10.9, HꢀC(6)); 7.03 (br. d, 3J(5,6) ¼ 10.8,
4
3
4
HꢀC(5)); 6.46 (d, J(3’,5’) ¼ 2.2, HꢀC(3’)); 6.39 (dd, J(5’,6’) ¼ 8.4, J(3’,5’) ¼ 2.2, HꢀC(5’)); 3.36 (d,
4J(5,Me) ¼ 1.1, MeꢀC(4)); 3.17 (s, MeOꢀC(2’)); 2.82 (sept., J ¼ 6.9, Me2CH); 2.82 (s, MeOꢀC(4’));
3
2.30 (s, MeCOꢀC(3)); 1.16 (d, J ¼ 6.9, Me2CH). 13C-NMR (75 MHz, CDCl3): 197.06 (MeCOꢀC(3));
3
191.53 (COꢀC(1)); 162.57 – 99.03 (10 azulene C, 6 benzene C); 55.70 (MeOꢀC(2’)); 55.51
(MeOꢀC(4’)); 38.44 (Me2CHꢀC(7)); 30.27 (MeCOꢀC(3)); 29.04 (MeꢀC(4)); 24.39 (Me2CHꢀC(7)).
.
EI-MS: 390 (88, Mþ ), 375 (100, [M ꢀ Me]þ), 373 (16), 347 (23, [M ꢀ MeCO]þ). Anal. calc. for C25H26O4
(390.48): C 76.90, H 6.71; found: C 76.82, H 6.83.
4. Syntheses. 4.1. 1-(5-Isopropyl-8-methylazulen-1-yl)alkan-1-ones 1 by Decarbonylation of the
Corresponding Carboxaldehydes 2 (cf. [6]). 4.1.1. 1-(5-Isopropyl-8-methylazulen-1-yl)ethanone (1c). To a
soln. of carboxaldehyde 2a (0.65 g, 2.56 mmol) in toluene (200 ml) was gradually added [RhCl(Ph3P)3]
(5.42 g, 5.86 mmol). After 20 h heating under reflux, the mixture was filtered through Celite. Toluene was

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distilled off and the volume-reduced filtrate (20 – 30 ml) purified by method B (hexane/t-BuOMe 15 :1)
[1]. Bulb-to-bulb distillation (120 – 1408/7 · 10ꢀ5 mbar) gave pure 1c (0.50 g, 86%). Black violet solid (cf.
Table). M.p. 77 – 788. Rf (hexane/AcOEt 3 :1) 0.44. IR (CHCl3): 2965m, 1645s, 1545w, 1523m, 1497m,
1463m, 1393s, 1372s, 1315s, 1178w, 1140w, 1062w, 1036w, 997w, 985w, 928w, 891m, 866w, 821w. 1H-NMR
4
3
3
(300 MHz, CDCl3): 8.35 (d, J(4,6) ¼ 2.1, HꢀC(4)); 8,10 (d, J(2,3) ¼ 4.3, HꢀC(2)); 7.60 (dd, J(6,7) ¼
11.0, 4J(4,6) ¼ 2.1, HꢀC(6)); 7.40 (d, 3J(6,7) ¼ 11.0, HꢀC(7)); 7.12 (d, 3J(2,3) ¼ 4.2, HꢀC(3)); 2.95
(sept., J ¼ 6.9, Me2CHꢀC(5)); 2.92 (s, MeꢀC(8)); 2.74 (s, MeCOꢀC(1)); 1.36 (d, J ¼ 6.9, Me2CHꢀC(5)).
13C-NMR (75 MHz, CDCl3): 196.66 (MeCOꢀC(1)); 149.79 – 117.29 (10 azulene C); 37.75
(Me2CHꢀC(5)); 30.39 (MeCOꢀC(1)); 28.60 (MeꢀC(8)); 24.35 (Me2CHꢀC(5)). GC/MS: 226 (29,
.
Mþ ), 211 (100, [M ꢀ Me]þ), 196 (9, [M ꢀ 2 Me]þ), 183 (4), 167 (6), 165 (8), 152 (9). Anal. calc. for
C16H18O (226.32): C 84.91, H 8.02; found: C 84.90, H 8.07.
4.1.2. (5-Isopropyl-8-methylazulen-1-yl)phenylmethanone (1d). Carboxaldehyde 2b was decarbon-
ylated as described for 2a. For main data, see Table.
4.1.3. 1-(5-Isopropyl-8-methylazulen-1-yl)-2,2-dimethylpropan-1-one (1f). The corresponding car-
boxaldehyde (see compound 2d in [1]) was decarbonylated as described for 2a. For main data, see Table.
4.2. 1,1’-[Methylenebis(5-isopropyl-8-methylazulene-3,1-diyl)]bis[2,2-dimethylpropan-1-one] (7f)7).
We applied the procedure of Takekuma, Yamamoto, and co-workers [7] (see also [8]). 7f: Red crystals.
M.p. 187 – 1888 (EtOH). Rf (Alox, toluene/t-BuOMe 30 :1) 0.34. IR (KBr): 3082vw, 2959s, 2929s, 2902m,
2868m, 1664s, 1637s, 1545m, 1521m, 1476m, 1459s, 1407s, 1363s, 1286w, 1250w, 1156m, 1119w, 1076m,
1
4
978m, 921w, 847m, 815w, 789m, 704w, 630w, 565w. H-NMR (300 MHz, CDCl3): 8.41 (d, J (6,8) ¼ 2.0,
HꢀC(8)); 7.59 (s, HꢀC(2)); 7.49 (dd, 3J (5,6) ¼ 10.8, J (6,8) ¼ 2.0, HꢀC(6)); 7.16 (d, 3J (5,6) ¼ 10.9,
4
HꢀC(5)); 4.79 (s, CH2); 3.03 (sept., J ¼ 6.9, Me2CHꢀC(7)); 2.67 (s, MeꢀC(4)); 1.29 (s,
Me3CCOꢀC(3)); 1.28 (d, J ¼ 6.9, Me2CHꢀC(7)). 13C-NMR (75 MHz, CDCl3): 212.59
(Me3CCOꢀC(3)); 146.51 – 127.10 (20 azulene C); 45.03 (Me3CCOꢀC(3)); 38.00 (Me2CHꢀC(7));
.
28.73 (Me3CCOꢀC(7)); 28.11 (MeꢀC(4)); 26.02 (CH2); 24.56 (Me2CHꢀC(7)). EI-MS: 548 (12, Mþ ),
491 (100, [M ꢀ Me3C]þ), 217 (24). Anal. calc. for C39H48O2 (548.81): C 85.35, H 8.82; found: C 85.63, H
8.56.
Table. 1-(5-Isopropyl-8-methyl-azulen-1-yl)alkan-1-ones 1 by Decarbonylation of the Corresponding Carbox-
aldehydes 2
Molar ratios
Reaction conditions
Purificationb) Yield [%] Physical data
reac- [RhCl(Ph3P)3] solvent conc.
time temp.
[react./solv.]a) [h] [8]
M.p. [8] d(C¼O)
tant
1
[ppm]c)
1c
2.3
toluene 1 : 300
20
reflux CC(A)d),
86
77 – 78 196.66
CC(B)e),
dist.f)
1d 1
1f
2.6
2.7
toluene 1 : 120
toluene 1 : 180
20
28
reflux CC(B)g),
dist.h)
reflux CC(B)i),
CC(B)e),
84
92
78 – 80 194.27
56 – 57 212.39
1
dist.f)
a) Reactant ratio [g]/solvent [ml]. b) For A and B, see [1] (Exper. Part). c) In CDCl3. d) Toluene (cf. [1]).
e) Hexane/t-BuOMe 15 : 1 (cf. [1]). f) Bulb-to-bulb distillation at 120 – 1408/high vacuum. g) Hexane/AcOEt
i
50 : 1. h) Bulb-to-bulb distillation at 140 – 1608/high vacuum. ) CH2Cl2.
4.2.1. DDQ Oxidation of 7f (see 7)). Product 5f. Bis(7-isopropyl-4-methyl-3-pivaloylazulen-1-
yl)methanone (¼1,1’-[Carbonylbis(5-isopropyl-8-methylazulene-3,1-diyl)]bis[2,2-dimethylpropan-1-
one]; 5f): See compound 4d in [1].

1582
Helvetica Chimica Acta – Vol. 93 (2010)
REFERENCES
[1] R. Sigrist, H.-J. Hansen, Helv. Chim. Acta 2010, 93, 1545.
[2] T. Okajima, S. Kurokawa, Chem. Lett. 1997, 69.
[3] F. Gerson, M. Scholz, H.-J. Hansen, P. Uebelhart, J. Chem. Soc., Perkin Trans. 2, 1995, 215.
[4] D. Sperandio, H.-J. Hansen, Helv. Chim. Acta 1995, 78, 765.
[5] K. Hafner, H. Pelster, J. Schneider, Liebigs Ann. Chem. 1961, 650, 62.
[6] R. A. Fallahpour, R. Sigrist, H.-J. Hansen, Helv. Chim. Acta 1995, 78, 1408.
[7] Y. Matsubara, M. Morita, S. Takekuma, Z. Zhao, H. Yamamoto, T. Nozoe, Bull. Chem. Soc. Jpn.
1991, 64, 2865.
[8] H. Arnold, K. Pahls, Chem. Ber. 1956, 89, 121.
Received January 25, 2010