A New Benzannulation Reaction of Azoaromatics

Article abstract of DOI:10.1055/s-0034-1380450

The BHQ benzannulation reaction of azo-substituted (2-allylaryl)trichloracetates, leading to azo-naphthalenes, is described. The scope and limitations of this new synthesis of azoaromatics is discussed.

Full text of DOI:10.1055/s-0034-1380450

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A New Benzannulation Reaction of Azoaromatics
Omer K. Rasheed
James Raftery
Peter Quayle*
R
R
R
N
N
N
N
N
N
[Cu]
School of Chemistry, University of Manchester,
Oxford Road, Manchester M13 9PL, UK
peter.quayle@manchester.ac.uk
Cl3COO
R = F, Cl, Br, I, H, Me, OH
HO
Cl
Received: 04.04.2015
Accepted after revision: 26.05.2015
Published online: 10.07.2015
Specifically, the elaboration of triflate derivatives of
phenols 3, using palladium-catalysed cross-coupling reac-
tions, has little precedent.3a–f More generally, the Stille- and
Suzuki-type coupling of the analogous halo, tin, and boron
derivatives of azo-substituted aromatics is at an embryonic
stage of development.3g,h In addition, although the ability of
the azo group to facilitate C–H activation was realized some
time ago,4 it is only recently that synthetic applications
have emerged.5 Likewise, the generation of organolithium
reagents derived from azo-functionalised aromatics either
by well-established halogen–metal exchange6a,b or Snieckus
DoG-lithiation6c is also underrepresented. The application
of dearomatisation strategies, which again utilises the reac-
tion between electropositive organometallics (organoli-
tiums/Grignard reagents) with an electron-deficient azo-
aromatic has also met with limited application, presumably
because of the intervention of competing chemistry at the
azo-group.6c,7a,b, This aberrant reactivity reflects the ten-
dency of the azo group to undergo electron-transfer reac-
tions with organometallics derived from the more elec-
tropositive metals.7b
Recently, we disclosed a new, transition-metal-cata-
lysed benzannulation reaction in which (ortho-allyl)aryl
trihaloacetates were found to participate in a radical cas-
cade sequence which ultimately results in the formation of
1-halo-naphthalene derivatives (the Bull–Hutchings–
Quayle or ‘BHQ reaction’).8a This transformation is quite
general in scope and proceeds well with substrates possess-
ing one or more of the more common organic functional
groups (aldehyde, nitro, ester etc., Scheme 2).
DOI: 10.1055/s-0034-1380450; Art ID: st-2015-s0240-c
Abstract The BHQ benzannulation reaction of azo-substituted (2-allyl-
aryl)trichloracetates, leading to azo-naphthalenes, is described. The
scope and limitations of this new synthesis of azoaromatics is dis-
cussed.
Key words benzannulation, ATRC, azo, cyclisation, copper, carbene,
radical
During a programme of research concerned with the
development of functionalised molecular sensors for the
detection of metal ions in biological systems we had occa-
sion to prepare azo dyes which incorporated extended
naphthalene π-systems.1 Although there is an extensive lit-
erature concerning the preparation of azo dyes – most no-
tably via the one-step diazo coupling chemistry as adum-
brated by Griess2 – downstream transformation of phenols
3, the usual products of these azo coupling reactions, by
way of carbon–carbon bond formation has not been exten-
sively investigated (Scheme 1).
OH
NH2
OH
X
X
Y
X
Y
Y
N
1. NaNO2, HCl
N
+
2. NaOH, H2O
0 °C
Z
X
Z
1
Y
3
a: X ,Y, Z = H, H, F (93%)
2
b: X ,Y, Z = H, H, Cl (87%)
c: X ,Y, Z = H, H, Br (87%)
d: X ,Y, Z = H, H, I (92%)
e: X ,Y, Z = H, Me, H (94%)
f: X ,Y, Z = H, H, OH (91%)
g: X ,Y, Z = H, H, NO2 (94%)
h: X ,Y, Z = i-Pr, H, H (96%)
With this development in mind we wondered whether
the BHQ reaction could be applied to the synthesis of
benzannulated azo compounds.8f We presumed that the
requisite ortho-allyl phenols for the intended BHQ se-
quence would be available by classical ortho-Claisen rear-
rangement chemistry,9 a process which does not require
Scheme 1 Azo-coupling reactions
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2806–2810

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O. K. Rasheed et al.
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the intervention of highly polarized organometallic inter-
mediates (Scheme 3). In the event of allylation of the readily
available azo dyes 3, which were prepared via standard di-
azo coupling reactions,10 was best accomplished, DMSO us-
ing KOH as base,15 in quantitative yields (Scheme 3,Table 1).
Somewhat surprisingly there is little literature prece-
dent11 for the ortho-Claisen rearrangement of azoaromatics
and attempted thermolysis of ethers 8 in N,N-diethylani-
line, as usually prescribed for this type of rearrangement,
merely afforded a complex mixture of products or starting
material depending upon the exact reaction conditions em-
ployed.
OH
R
R
R
OH
OCOCCl3
X
Cl3CCOCl
base
i)
base
ii)
Δ
6
4
5
[ M ]
Cl
CO2 x 2 HCl
R = OR1, halogen, NO2, CO2R1, CHO, COR1 etc.
[ M ] = redox-active TM catalyst
R
7
Conversion of ethers 8 into phenols16 9 was, however,
observed in good isolated yields (79–97%) when the rear-
rangement was conducted in the presence of Et2AlCl (2.2
equiv) in CH2Cl2 at 20 °C for 15 hours.12 These reactions
Scheme 2 The ‘BHQ’ benzannulation sequence
O
Y
Y
X
X
Y
Y
X
X
Y
Y
X
X
Cl
CCl3
Et3N
Br
Et2AlCl
Z
N
Z
N
3
Z
N
KOH
DMSO
r.t. 3 h
CH2Cl2
r.t., 15 h
Et2O
0 °C, 3 h
N
O
N
OH
N
OCOCCl3
9
10
8
12
Diglyme
162 °C, 3 h
Y
Y
X
X
Cl
Z
N
N
11
O
O
OCOCCl3
OH
Cl
CCl3
Et3N
N
Et2AlCl
N
N
N
N
N
CH2Cl2
Et2O
0 °C, 3 h
r.t., 15 h
Cl3OCO
O
HO
10g
9g
8g
12
Diglyme
162 °C, 3 h
Cl
O
N
CuCl
N
CCl3
N
N
Et3N
11g
13
Cl
12
Scheme 3 Benzannulation reaction leading to azo-aromatics
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O. K. Rasheed et al.
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were not optimized as they provided material in sufficient
quantity and purity for the pivotal BHQ benzannulation re-
action.
Noteworthy is the observation that the bisallyl ether 8g
was utilized effectively in a ‘two-directional’ BHQ benz-
annulation reaction. Here, a double ortho-Claisen rear-
rangement of 8g afforded the diol 9g, which ultimately re-
sulted in the isolation of the azo compound 11g after
benzannulation (72% yield for the benzannulation step).
This outcome is to be compared with that from the nitro-
substituted substrate 8i, which proved to be wholly resis-
tant towards benzannulation.
Unfortunately, attempted extension of this methodolo-
gy to the rearrangement of the naphthol derivative 16
proved to be highly capricious. In this case thermolysis of
16 in N,N-diethylaniline (180 °C, 15 h) merely afforded the
phenol 18 in excellent yield (88%),13 while the use of Et2AlCl
(2.2 equiv, CH2Cl2, 0–20 °C) as promotor resulted in the for-
mation of the desired rearranged product 17 (26% isolated
yield), together with minor quantities (17% isolated yield) of
the phenol 18 (Scheme 4).
Table 1 Yields for Claisen-BHQ Sequences
Entry
X
Y
Z
Yield of 8 Yield of 9 Yield of 10 Yield of 11
(%) (%) (%) (%)
1
2
3
4
5
6
7
8
9
H
H
H
94
83
81
78
H
Me
H
H
93
92
94
88
88
88
92
81
84
87
91
81
83
79
87
–
81
83
89
80
81
80
82
–
77
80
87
80
77
72
–
H
Cl
F
H
H
H
H
Br
I
H
H
H
H
OH
H
i-Pr
H
H
H
NO2
–
Br
Having established the feasibility of performing the or-
tho-Claisen rearrangement on a range of azo compounds
the utility of the substituted phenols 9 in the BHQ reaction
was next examined. Conversion of the phenols 9 into their
respective trichloroacetates 1017 was readily achieved [Et3N
(1.2 equiv); Cl3CCOCl (1.2 equiv), Et2O, 0 °C] in good yields
(80–90%). Fortunately, the crude products from the acyla-
tion reactions were again of sufficient purity to be used in
the pivotal benzannulation reaction as attempted chroma-
tography can lead to deacylation. In passing, it should be
noted that the use of an excess of triethylamine/trichloro-
acetyl chloride should be avoided in the acylation reaction
as oxidation of the amine, generating the vinylogous amide
13, is relatively facile.13
Conversion of the trichloroacetates 10 into the benzan-
nulated products 11 proved to be generally uneventful and
proceeded to completion over a period of three hours when
heated in the presence of the preformed catalyst 128b (5
mol%) at 162 °C in anhydrous diglyme.18 The overall re-
giochemical outcome of the ortho-Claisen–BHQ benzannu-
lation sequence was also confirmed in the case of 11a by
way of single-crystal X-ray structure determination (Figure
1).
HO
1. NaNO2, HCl
Br
N
+
N
2c
KOH
2. NaOH, H2O
0 °C
OH
DMSO
87%
14
89%
15
Br
N
Br
N
a) Et2AlCl, CH2Cl2, r.t., 24 h
17: 26%; 18: 17%
OH
N
+
b) Et2NPh, 180 °C
OH
18: 88%
N
18
O
17
16
Scheme 4 Synthesis of rearranged azo-naphthol derivative via Claisen
rearrangement
It should be noted that possible limitation of this chem-
istry is evident in that attempted rearrangement of the
naphthol derivative 17, where the presence of a proximal
azo functional group inhibited the trichloroacetylation
step.
In conclusion we have demonstrated that an ortho-
Claisen–BHQ benzannulation sequence can be applied to
the synthesis of benzofused azoaromatics. In most cases
the benzannulation proceeds in high yields, complements
existing methodology,14 and enables the synthesis of func-
tionalised azoaromatics. Application to the synthesis of be-
spoke azonaphthalenes is now in progress.
Figure 1 Single-crystal X-ray structure of 11a
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Acknowledgment
Raftery, J.; Little, M. S.; McDouall, J. J. W.; Yeates, S. G.; Quayle, P.
Chem. Commun. 2015, 51, 6115. ATRP reactions of azo-contain-
ing substrates is documented: (f) Fang, L.; Chen, S.; Guo, X.;
Zhang, Y.; Zhang, H. Langmuir 2012, 28, 9767.
Financial support from the University of Manchester is gratefully ac-
knowledged. The UoM thanks the EPSRC (grant number
EP/K039547/1) for the provision of Bruker NMR spectrometers and an
Agilent SuperNova X-ray diffractometer.
(9) (a) Majumdar, K. C.; Nandi, R. K. Tetrahedron 2013, 69, 6921.
(b) Ichikawa, H.; Maruoka, K. Aliphatic and Aromatic Claisen
Rearrangement, In The Claisen Rearrangement; Hiesermann, M.;
Nubbermeyer, U., Eds.; Wiley-VCH: Weinheim, 2007, Chap. 3,
45.
Supporting Information
(10) (a) Florea, S.; Rudolf, W. D.; Chivu, M. Anal. Univ. Craiova, Ser.
Chim. 2005, 34, 1; Chem. Abstr. 2005, 146, 379752. For alterna-
tive approaches to related substrates, see: (b) Odabaşoğlu, M.;
Turgut, G.; Karadayi, N.; Büyükgüngör, O. Dyes and Pigments
2005, 64, 271.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1380450. Experimental procedures
for all new compounds are included, as well as a cif file for compound
11a (CCDC 1048487).
S
u
p
p
ortioInfgrmoaitn
S
u
p
p
ortiInfogrmoaitn
(11) Bender, D. R.; Kanne, D.; Frazier, J. D.; Rapoport, H. J. Org. Chem.
1983, 48, 2709.
(12) Giger, R.; Allain, R.; Rey, M.; Dreiding, A. S. Helv. Chim. Acta
1970, 53, 120.
(13) For a related ipso-substitution reaction during a Claisen rear-
rangement, see: Anjaneyulu, A. S. R.; Isaa, B. M. J. Chem. Soc.,
Perkin Trans. 1 1990, 993.
(14) Hegele, P.; Santhamma, B.; Schnakenburg, G.; Fröhlich, R.;
Kateava, O.; Nieger, M.; Kotsis, K.; Neese, F.; Dötz, K. H. Organo-
metallics 2010, 29, 672.
References and Notes
(1) For applications of related compounds, see: Quandt, G.; Höner,
G.; Pabel, J.; Dine, J.; Eder, M.; Wanner, K. T. J. Med. Chem. 2014,
57, 6809.
(2) (a) Griess, P. Justus Liebigs Ann. Chem. 1866, 137, 39.
(b) Maerino, E. Chem. Soc. Rev. 2011, 40, 3835. (c) Zollinger, H.
Azo Coupling Reactions, In Diazo Chemistry I; VCH: Weinheim,
1994, 305.
(15) General Method for the Preparation of Allylated Ethers 8
To a stirred mixture of powdered KOH (5 equiv) in DMSO was
added the diazo compound (1 equiv). Allyl bromide (2 equiv)
was then added to the mixture. The reaction mixture was
stirred for 3 h at r.t. and then poured into H2O. The organic
material was extracted into CH2Cl2 (50 mL), and the organic
layer was washed with brine (2 × 20 mL), H2O (1 × 20 mL), dried
(MgSO4), and concentrated in vacuo. The crude product was
purified by flash chromatography to give products 8a–i
Synthesis of (E)-1-[2-(Allyloxy)phenyl]-2-phenyldiazene (8a)
Yield 94%; mp 70–72 °C. 1H NMR (300 MHz, CDCl3): δ = 4.64 (2
H, dt, J = 5, 1 Hz), 5.34 (1 H, dq, J = 10, 1 Hz), 5.47 (1 H, dq, J = 17,
2 Hz), 5.95–6.23 (1 H, m) 6.97–7.14 (2 H, m), 7.40–7.58 (3 H, m),
7.81–8.01 (4 H, m) ppm. 13C NMR (75 MHz, CDCl3): δ = 69.1,
114.9, 118.1, 122.5, 124.6, 128.9, 130.3, 132.7, 147.1, 152.7,
161.1 ppm. MS (ES+): m/z = 239 [M + Na]+. HRMS (ES+): m/z
calcd for [C15H14N2O + H]: 239.1179; found: 239.1182. IR (ATR):
(3) (a) Gøgsig, T. M.; Kleimark, J.; Nilsson, L.; Korsager, S.;
Lindhardt, A. T.; Norrby, P.-O.; Skrydstrup, T. J. Am. Chem. Soc.
2012, 134, 443. (b) Casa-Solvas, J. M.; Vargas-Berenguel, A. Tet-
rahedron Lett. 2008, 49, 6778. (c) Ma, X.; Wang, Q.; Tian, H. Tet-
rahedron Lett. 2007, 48, 7112. (d) Harvey, J. H.; Butler, B. K.;
Trauner, D. Tetrahedron Lett. 2007, 48, 1661. (e) Okanao, K.;
Tsutsumi, O.; Shishido, A.; Ikeda, T. J. Am. Chem. Soc. 2006, 128,
15368. (f) Liao, L.-X.; Stellacci, F.; McGrath, D. V. J. Am. Chem.
Soc. 2004, 126, 2181. For
a representative example, see:
(g) Strueben, J.; Gates, P. J.; Staubitz, A. J. Org. Chem. 2014, 79,
1719. (h) Pérez-Miqueto, J.; Telleria, A.; Muñoz-Olasagasti, M.;
Altube, A.; Garcia-Lecina, E.; de Cózar, A.; Freixa, Z. Dalton Trans.
2015, 2075.
(4) (a) Heck, R. F. J. Am. Chem. Soc. 1968, 90, 313. (b) Cope, A. C. J.
Am. Chem. Soc. 1965, 87, 3272. (c) Kleiman, J. P.; Dubeck, M. J.
Am. Chem. Soc. 1963, 85, 1544. (d) Bagga, M. M.; Flannigan, W.
T.; Knox, G. R.; Pauson, P. L. J. Chem. Soc. C 1969, 1534.
ν
max = 1496, 1579, 1598, 3023 cm–1
.
(5) (a) Majhi, B.; Kundu, D.; Ahammaed, S.; Ranu, B. C. Chem. Eur. J.
2014, 20, 9862. (b) Qian, C.; Lin, D.; Deng, Y.; Zhang, X-Q.; Jiang,
H.; Miao, G.; Tang, X.; Zeng, Y. Org. Biomol. Chem. 2014, 12,
5866. (c) Lian, Y.; Bergman, R. G.; Lavis, L. D.; Ellman, J. A. J. Am.
Chem. Soc. 2013, 135, 7122; and references cited therein.
(6) (a) Koźlecki, T.; Syper, L.; Wilk, K. A. Synthesis 1997, 681.
(b) Kano, N.; Komatsu, F.; Yamamura, M.; Kawashima, T. J. Am.
Chem. Soc. 2006, 128, 7097. The direct lithiation of azobenzene
derivatives has recently been reported, see: (c) Nguyen, T. T. T.;
Boussonnière, A.; Banaszak, E.; Castanet, A.-S.; Nguyen, K. P. P.;
Mortier, J. J. Org. Chem. 2014, 79, 2775.
(16) General Procedure for the Preparation of o-Claisen-Rear-
ranged Phenols 9
To a stirred solution of the allyl ether (1 mmol) in dry CH2Cl2
(10 mL) was added Et2AlCl (2 equiv) at 0 °C under an atmo-
sphere of dry nitrogen. The reaction mixture was stirred at r.t.
for 15 h and then quenched by the careful addition of a sat.
solution of Na/K tartrate tetrahydrate (10 mL). The organic layer
was separated and the aqueous phase extracted with EtOAc
(2 × 20 mL). The combined organic extracts were washed (brine,
3 × 20 mL), then H2O (3 × 20 mL), and dried over MgSO4. The
crude mixture was purified by column chromatography (40%
CH2Cl2 in hexane) to give the products 9a–h.
(7) (a) Colonna, M.; Risalti, A. Gazz. Chim. Ital. 1956, 86, 698.
(b) Risaliti, A.; Bozzini, S. Ann. Chim. 1964, 54, 685. (c) Holm, T.
Acta Chem. Scand. B 1983, 37, 567.
(E)-2-Allyl-4-(phenyldiazenyl)phenol (9a)
Yield 83%; crystalline; mp 91.7–93.0 °C (lit. 89–90 °C) was
obtained by column chromatography (40% CH2Cl2 in hexane). 1H
NMR (300 MHz, CDCl3): δ = 3.52 (2 H, d, J = 6 Hz), 5.21 (1 H, t, J =
1 Hz), 5.26 (1 H, dd, J = 8, 1 Hz), 6.09 (1 H, ddt, J =16, 10, 6 Hz),
6.94 (1 H, dd, J = 9, 3 Hz, CH, ArH), 7.44–7.56 (3 H, m, CH, ArH),
7.76–7.82 (2 H, m, CH, ArH), 7.89 (2 H, dd, J = 8, 2 Hz, CH, ArH)
ppm. 13C NMR (75 MHz, CDCl3): δ = 35.1, 116.2, 117.1, 122.5,
123.5, 125.1, 129.1, 130.3, 135.7, 126.1, 147.1, 152.7, 156.9
(8) (a) Bull, J. A.; Hutchings, M. G.; Quayle, P. Angew. Chem. Int. Ed.
2007, 46, 1869. (b) Bull, J. A.; Hutchings, M. G.; Lujan, C.; Quayle,
P. Tetrahedron Lett. 2008, 49, 1352. (c) Bull, J. A.; Hutchings, M.
G.; Lujan, C.; Quayle, P. Tetrahedron Lett. 2009, 50, 3617.
(d) Little, M.; Lan, H.; Raftery, J.; Morrison, J. J.; McDouall, J. J.
W.; Yeates, S. G.; Quayle, P. Eur. J. Org. Chem. 2013, 6038.
(e) Heard, K. W. J.; Morrison, J. J.; Weston, L.; Lo, C. H.; Pirvu, L.;
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2806–2810

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O. K. Rasheed et al.
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ppm. MS (ES+): m/z = 239 [M + H]+. MS (ES–): m/z = 237 [M – H]+.
HRMS (ES–): m/z calcd for [C15H14N2O – H]: 237.1025; found:
237.1033. IR (ATR): νmax = 1339, 1444, 1465, 1502, 1592, 1737,
34.1, 117.3, 121.8, 122, 122.9, 125.4, 129.1, 131.3, 134.7, 132.9,
151.2, 150.2, 152.5, 160.2 ppm. IR (ATR): νmax = 1351, 1459,
1487, 1541, 1584, 1401, 1799, 2984 cm–1
.
3068 cm–1
.
(18) General Procedure for Benzannulation Reactions (11)
The trichloroacetate (0.5 mmol, 1 equiv) was heated with the
catalyst 12 (5 mol%) in diglyme (0.5 mL) at 162 °C for 3 h under
an atmosphere of dry nitrogen. The reaction mixture was
allowed to cool to r.t. and then purified directly by flash column
chromatography (100% PE) to give the products 11a–g.
(17) General Procedure for Trichloroacylation (10)
To the stirred solution of 9 (1 equiv) and Et3N (1.2 equiv) in dry
Et2O was added dropwise trichloroacetyl chloride (1.2 equiv) at
0 °C. After 3 h at this temperature the reaction mixture was
quenched by the addition of H2O (20 mL). The quenched reac-
tion mixture was extracted with Et2O (50 mL), and the organic
layer was separated, washed [NaHCO3; 3 × 20 mL of a sat. solu-
tion), brine (3 × 20 mL), and H2O (3 × 20 mL)], dried (MgSO4),
and concentrated in vacuo to afford the crude products 10a–h,
which were of sufficient purity to be used in the next step.
(E)-2-Allyl-4-(phenyldiazenyl)phenyl 2,2,2-Trichloroacetate
(10a)
(E)-1-(5-Chloronaphthalen-2-yl)-2-phenyldiazene (11a)
Yield 78%; orange crystals; mp 113–114 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.41–7.59 (4 H, m, CH, ArH), 7.66 (1 H, dd, J = 7, 1 Hz,
CH, ArH), 7.89–8.04 (3 H, m, CH, ArH), 8.18 (1 H, dd, J = 9, 2 Hz,
CH, ArH), 8.38 (1 H, d, J = 9 Hz, CH, ArH), 8.48 (1 H, d, J = 2 Hz,
CH, ArH) ppm. 13C NMR (75 MHz, CDCl3): δ = 118.6, 122.9,
125.7, 126.7, 127.2, 127.6, 128.5, 129.2, 131.2, 131.9, 132.1,
132.8, 150.6, 152.6 ppm. MS (ES+): m/z = 267 [M + H]+. HRMS
1
Brownish oil; 81% yield. H NMR (300 MHz, CDCl3): δ = 3.50 (2
H, dd, J = 6, 1 Hz), 5.15 (1 H, dq, J = 8, 1 Hz), 5.19 (1 H, m), 5.92–
6.07 (1 H, m), 7.35 (1 H, dd, J = 7, 2 Hz), 7.51–7.55 (3 H, m, CH),
7.87–7.97 (4 H, m, CH, ArH) ppm. 13C NMR (75 MHz, CDCl3): δ =
(ES+): m/z calcd for [C16H11N2Cl
+ H]: 267.0684; found:
267.0674. Anal. Calcd (%) for C16H11N2Cl: C, 72.0; H, 4.1; N, 10.5.
Found: C, 71.8; H, 4.0; N, 10.3%. IR (ATR): νmax = 1286, 1334,
1415, 1457, 1570, 3011 cm–1
.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2806–2810