9,10-Dioxa-1,2-diaza-anthracene derivatives from tetrafluoropyridazine

Article abstract of DOI:10.3762/bjoc.6.45

Reaction of tetrafluoropyridazine with catechol gives a tricyclic 9,10-dioxa-1,2-diaza-anthracene system by a sequential nucleophilic aromatic substitution ring annelation process, further extending the use of perfluoroheteroaromatic derivatives for the synthesis of unusual polyfunctional heterocyclic architectures. The tricyclic scaffold reacts with amines and sodium ethoxide providing a short series of functional 9,10-dioxa-1,2-diaza-anthracene systems.

Full text of DOI:10.3762/bjoc.6.45

9,10-Dioxa-1,2-diaza-anthracene derivatives from
tetrafluoropyridazine
Graham Pattison1, Graham Sandford*1, Dmitrii S. Yufit2,
Judith A. K. Howard2, John A. Christopher3 and David D. Miller3
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, No. 45.
1Department of Chemistry, University of Durham, South Road,
Durham, DH1 3LE, United Kingdom, 2Chemical Crystallography
Group, Department of Chemistry, University of Durham, South Road,
Durham, DH1 3LE, U.K. and 3GlaxoSmithKline R&D, Medicines
Research Centre, Gunnels Wood Road, Stevenage, Hertfordshire,
SG1 2NY, United Kingdom
doi:10.3762/bjoc.6.45
Received: 05 February 2010
Accepted: 14 April 2010
Published: 06 May 2010
Guest Editor: D. O'Hagan
Email:
Graham Sandford* - Graham.Sandford@durham.ac.uk
© 2010 Pattison et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
benzodioxinopyridazine; 9,10-dioxa-1,2-diaza-anthracene;
heterocyclic synthesis; nucleophilic aromatic substitution;
perfluoroheteroaromatic; tetrafluoropyrazine
Abstract
Reaction of tetrafluoropyridazine with catechol gives a tricyclic 9,10-dioxa-1,2-diaza-anthracene system by a sequential nucleo-
philic aromatic substitution ring annelation process, further extending the use of perfluoroheteroaromatic derivatives for the synthe-
sis of unusual polyfunctional heterocyclic architectures. The tricyclic scaffold reacts with amines and sodium ethoxide providing a
short series of functional 9,10-dioxa-1,2-diaza-anthracene systems.
Introduction
Drug discovery programmes are continually searching for tively low level of structural diversity in all known organic
viable synthetic routes to highly novel classes of heterocyclic structures [3] and, indeed, the perceived lack of structural
compounds with the aim of exploring chemical ‘drug-like’ diversity in pharmaceutical companies’ compound collections
space [1] and uncovering valuable biological activity for hit-to- have often been suggested to be among the bottlenecks in drug
lead generation of new chemical entities by parallel synthesis discovery programmes [4]. Methodology for the ready synthe-
techniques. The wide variety of relatively simple heterocyclic sis of new organic frameworks is still required and, in this
structural types that have not been synthesised [2], the rela- context, heterocyclic scaffolds based on novel molecular archi-
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Beilstein J. Org. Chem. 2010, 6, No. 45.
Scheme 1: Synthesis of novel tricyclic heterocycles from pentafluoropyridine.
tecture that bear multiple functionality and can be rapidly (3) with catechol (4). In principle, two possible systems 5 and 6
processed into many analogues by parallel synthesis are particu- may be formed depending upon the regioselectivity of the
larly valuable [5,6].
nucleophilic aromatic substitution processes (Scheme 2).
In a continuing research programme, we have demonstrated that Both 5 and 6 have ring fluorine atoms present that may, in prin-
perfluorinated heteroaromatic derivatives are very useful ciple, be displaced by nucleophiles which could lead to the syn-
starting scaffolds for the synthesis of a variety of heteroaro- thesis of many analogues of these systems. The dioxa-1,2-diaza-
matic [7], [5,6] and [6,6]-bicyclic [8-11], and polycyclic hetero- anthracene (or 3,4-difluorobenzo[5,6][1,4]dioxino[2,3-
cyclic systems [12]. Perfluoroheteroaromatic derivatives are c]pyridazine also referred to as benzodioxinopyridazine)
either commercially available or can be accessed by halogen- systems are very rare heterocyclic structures and only a handful
exchange processes by reaction of the corresponding perchloro- of analogues based upon this molecular skeleton have been
heteroaromatic system and potassium fluoride [13]. No special synthesised, mainly by the reaction of chlorinated pyridazines
techniques for handling perfluoroheteroaromatic compounds are with catechol [14-16].
required, apart from the usual laboratory precautions, because
these systems are generally volatile, colourless liquids. We In this paper, we describe the synthesis of dioxa-1,2-diaza-
established that highly novel tricyclic scaffolds, such as the anthracene derivatives by the sequential reaction of commer-
relatively uncommon dipyrido[1,2-a:3′,4′-d]imidazole system 1, cially available tetrafluoropyridazine with catechol, and a short
could be synthesised from pentafluoropyridine in a single step series of nucleophiles.
[12], exemplifying our general strategy for the synthesis of
highly novel classes of polyfunctional heterocyclic compounds. Results and Discussion
Several dipyrido[1,2-a:3′,4′-d]imidazole analogues 2 were Initially, we carried out reactions of tetrafluoropyridazine (3)
prepared by the displacement of the remaining ring fluorine with one and two equivalents of sodium phenoxide as a model
atoms by nucleophilic aromatic substitution processes substrate for catechol (Scheme 3).
(Scheme 1).
Reaction of one equivalent of sodium phenoxide with (3) gave
We were interested in further expanding the use of highly fluor- product 7 arising from substitution of fluorine located at the site
inated heterocycles for the preparation of novel heterocyclic para to activating ring nitrogen, consistent with earlier studies
structures and focussed upon the synthesis of ring fused systems involving reactions between tetrafluoropyridazine and various
that could be derived from the reaction of tetrafluoropyridazine nucleophiles [13]. Similarly, reaction of two equivalents of
Scheme 2: Synthetic route to dioxa-diaza-anthracene derivatives.
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Beilstein J. Org. Chem. 2010, 6, No. 45.
Scheme 4: Synthesis of dioxa-1,2-diaza-anthracene scaffold 5.
by analogy to the outcome of reaction between 3 and excess
phenoxide. However, since nucleophilic aromatic substitution
reactions are frequently reversible [13], conversion of 6 must
occur via intermediate 5a and lead to the most thermodynamic-
ally stable product 5 (Scheme 5).
Scheme 3: Reactions of tetrafluoropyridazine 3 with sodium phen-
oxide.
sodium phenoxide gave the 4,5-diphenoxy derivative 8 by
displacement of both fluorine atoms that are attached to the sites The utility of the dioxa-1,2-diaza-anthracene system 5 as a scaf-
para to ring nitrogen atoms.
fold for array synthesis was assessed in representative reactions
with a short series of nucleophiles (Scheme 6).
In contrast, however, reaction of catechol (4) with tetra-
fluoropyridazine (3) under similar reaction conditions gave the Nucleophilic substitution of fluorine at the 4-position occurs
tricyclic system 5 arising from displacement of the 3- and regiospecifically to afford products 9a–c according to 19F NMR
4-fluorine atoms as the sole product according to a 19F NMR analysis of the corresponding reaction mixtures. The 19F NMR
analysis of the crude reaction mixture (Scheme 4). The resonances located at ca. −90 ppm are characteristic of fluorine
19F NMR displays two resonances at −96.4 and −151.9 ppm in atoms located at sites ortho to a ring nitrogen atom. X-ray crys-
accord with structure 5, whereas if the symmetrical 4,5-disubsti- tallography of the allylamino derivative 9b (Figure 1), and a
tuted product 6 had been formed only one resonance in the comparison of NMR spectral data, confirms the structures of
19F NMR spectrum at ca. −88 ppm (cf. 8) would have been these analogues.
observed.
The geometrical parameters of the molecule 9b are close to
It seems reasonable to assume that initial substitution occurs at expected values. The molecules of 9b in the crystal are linked
the 4-position of 3, analogous to the reaction between 3 and together by N–H···N hydrogen bonds in chains, parallel to the
phenoxide, to give intermediate 5a. At this point, we would [101] direction and π···π stacking interactions (shortest
expect cyclisation to occur at position 5 to give product 6, again interatomic distance C5···C3 is 3.336 Å), and short C–H···O
Scheme 5: Mechanism of formation of 5.
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Beilstein J. Org. Chem. 2010, 6, No. 45.
Scheme 6: Reactions of dioxa-1,2-diaza-anthracene scaffold 5 with nucleophiles.
Figure 1: Molecular structure of 4-allylamino-3-fluoro-9,10-dioxa-1,2-diaza-anthracene (9b).
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Beilstein J. Org. Chem. 2010, 6, No. 45.
contacts (C···O 3.387 Å) bind adjacent chains in the [100] and 7.7, H-3′); 13C NMR (175 MHz, CDCl3, δC): 116.4 (s, C-2′),
[010] directions, respectively.
124.9 (s, C-4′), 129.7 (s, C-3′), 137.2 (dd, 2JCF = 20.6, 3JCF =
12.9, C-4), 155.2 (s, C-1′), 160.1 (dd, 1JCF = 251.2, 4JCF = 6.8,
Again, the regiospecificity of these reaction processes occurs C-3); 19F NMR (658 MHz, CDCl3 δF): −88.2 (s); MS (ES+)
because of the activating effect of ring nitrogen directly m/z: 301 ([MH]+, 100%).
opposite the site of nucleophilic substitution.
Synthesis of 3,4-difluoro-9,10-dioxa-1,2-diaza-
Conclusions
anthracene (5)
A small range of dioxa-1,2-diaza-anthracene analogues 5 and 9 Catechol (0.80 g, 7.2 mmol) was dissolved in THF (20 mL) at
have been synthesised from tetrafluoropyridazine in two effi- 0 °C under an argon atmosphere with stirring and added to
cient steps, further expanding the application of highly fluorin- sodium hydride (0.35 g, 14.5 mmol, 60% dispersion in mineral
ated heterocycles for the synthesis of rare heterocyclic architec- oil). Tetrafluoropyridazine (1.00 g, 6.6 mmol) was added drop-
tures.
wise and the mixture stirred at 0 °C for 8 h. After this period,
the solvent was evaporated, and the crude material redissolved
in dichloromethane (25 mL) and water (25 mL). The organic
Experimental
Synthetic procedures for the preparation of all the new com- layer was separated and the aqueous layer extracted with
pounds described in this paper are given below.
dichloromethane (3 × 25 mL). The combined organic extracts
were then dried (MgSO4), filtered and evaporated to provide a
crude yellow material. Crystallisation from acetonitrile gave
3,4-difluoro-9,10-dioxa-1,2-diaza-anthracene (5) (1.09 g, 75%)
as white solid; mp 146–148 °C; Anal. Calcd for C8H11FN4O: C,
Reactions of tetrafluoropyridazine (3) with
sodium phenoxide
3,4,6-Trifluoro-5-phenoxypyridazine (7)
Phenol (0.17 g, 1.81 mmol) was dissolved in THF (20 mL) and 54.1; H, 1.8; N, 12.6%. Found: C, 54.0; H, 1.9; N, 12.6. IR,
added to sodium hydride (0.07 g, 1.8 mmol, 60% dispersion in νmax/cm−1: 1015, 1035, 1094, 1115, 1260, 1416, 1464, 1490,
mineral oil) which was cooled to 0 °C and stirred. Tetra- 1568, 1654; 1H NMR (400 MHz, CDCl3, δH): 7.13–7.06 (4 H,
fluoropyridazine (3) (0.25 g, 1.64 mmol) was added slowly and m, ArH); 13C NMR (100 MHz, CDCl3, δC): 117.0 (s, C-5),
the mixture stirred at 0 °C for 8 h. The solvent was evaporated 118.1 (s, C-6), 126.0 (s, C-7), 126.8 (s, C-8), 133.4 (dd, 2JCF =
and the crude material partitioned between dichloromethane 6.3 Hz, 3JCF = 6.3 Hz, C-4a), 136.8 (dd, 1JCF = 278.0 Hz,
(25 mL) and water (25 mL). The organic layer was separated 2JCF = 30.0 Hz, C-4), 138.6 (s, C-8a), 140.3 (s, C-9a), 154.5 (s,
and the aqueous layer extracted with dichloromethane C-10a), 156.9 (dd, 1JCF = 290 Hz, 2JCF = 8.0 Hz, C-3);
(3 × 25 mL). The combined organic extracts were then dried 19F NMR (376 MHz, CDCl3, δF): −96.4 (1F, d, 3JFF = 25.8 Hz,
(MgSO4), filtered and evaporated in vacuo to provide a crude F-3), −151.9 (1F, d, 3JFF = 25.9 Hz, F-4); MS (EI+) m/z: 222
yellow material. Column chromatography on silica gel using ([M]+, 10%), 138 (43), 74 (66), 63 (67), 50 (100).
hexane:ethyl acetate (4:1) as elutant gave 3,4,6-trifluoro-5-
Reaction of 3,4-difluoro-9,10-dioxa-1,2-diaza-
phenoxypyridazine (7) (0.25 g, 68%) as a colourless oil; Anal.
Calcd for C10H5F3N2O: C, 53.1; H, 2.2; N, 12.4%. Found: C, anthracene (5) with morpholine
53.2; H, 2.5; N, 12.2. 1H NMR (200 MHz, CDCl3, δH): 3-Fluoro-4-(morpholin-4-yl)-9,10-dioxa-1,2-diaza-
7.04–7.42 (5H, m, ArH); 19F NMR (188 MHz, CDCl3, δF): anthracene (9a)
−86.2 (1F, dd, 5JFF = 31.2 Hz, 4JFF = 23.7 Hz, F-6), −94.5 (1F, A mixture of 3,4-difluoro-9,10-dioxa-1,2-diaza-anthracene (5)
dd, 5JFF = 31.2 Hz, 3JFF = 23.7 Hz, F-3), −140.4 (1F, dd, 3JFF = (0.20 g, 0.90 mmol), morpholine (0.16 mL, 1.80 mmol) and
23.7 Hz, 4JFF = 23.7 Hz, F-4); MS (ES+) m/z: 227 ([MH]+, acetonitrile (2 mL) were placed in a 0.5–2 ml microwave vial
100%).
under an argon atmosphere and subjected to microwave irradi-
ation at 150 °C for 20 min. The mixture was partitioned
between dichloromethane (20 mL) and water (20 mL) and the
3,6-Difluoro-4,5-diphenoxypyridazine (8)
Using the procedure described above, phenol (0.32 g, 3.45 organic layer separated. The aqueous layer was then extracted
mmol), sodium hydride (0.138 g, 3.45 mmol, 60% dispersion in with dichloromethane (3 × 20 mL) to give a crude yellow ma-
mineral oil), tetrafluoropyridazine (0.25 g, 1.64 mmol) and THF terial. Column chromatography on silica gel using hexane:ethyl
(20 mL) gave 3,6-difluoro-4,5-diphenoxypyridazine (8) (0.29 g, acetate (2:1) as eluent gave 3-fluoro-4-(morpholin-4-yl)-9,10-
59%) as a white solid; mp 123–124 °C; Anal. Calcd for dioxa-1,2-diaza-anthracene (9a) (0.18 g, 71%) as white crystals;
C16H10F2N2O2: C, 64.0; H, 3.4; N, 9.3%. Found: C, 63.7; H, mp 207–208 °C; Found: [MH]+, 290.09345. C14H12FN3O3
3.5; N, 9.2. 1H NMR (700 MHz, CDCl3, δH): 6.80 (2H, d, 3JHH requires: [MH]+, 290.09355; 1H NMR (700 MHz, CDCl3, δH):
= 7.7, H-2′), 7.09 (1H, t, 3JHH = 7.7, H-4′), 7.23 (2H, t, 3JHH = 3.44 (4H, t, 3JHH = 4.4 Hz, H-2′), 3.84 (4H, t, 3JHH = 4.4 Hz,
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Beilstein J. Org. Chem. 2010, 6, No. 45.
Reaction of 3,4-difluoro-9,10-dioxa-1,2-diaza-
H-3′), 6.94 (1H, d, 3JHH = 7.6 Hz, ArH), 7.01 (1H, tm, 3JHH =
7.6 Hz, ArH), 7.06 (2H, m, ArH); 13C NMR (175 MHz, CDCl3, anthracene (5) with sodium ethoxide
δC): 50.4 (d, 4JCF = 4.0 Hz, C-2′), 67.3 (s, C-3′), 116.5 (s, C-5), 4-Ethoxy-3-fluoro-9,10-dioxa-1,2-diaza-anthracene
117.7 (s, C-8), 125.2 (s, C-6), 125.9 (s, C-7), 126.0 (d, 2JCF = (9c)
25.4 Hz, C-4), 134.6 (d, 3JCF = 8.9 Hz, C-4a), 139.4 (s, C-8a), Using the procedure described above, 3,4-difluoro-9,10-dioxa-
140.9 (s, C-10a), 153.7 (s, C-9a), 159.0 (d, 1JCF = 237.7 Hz, 1,2-diaza-anthracene (5) (0.10 g, 0.45 mmol), sodium ethoxide
C-3); 19F NMR (658 MHz, CDCl3, δF): −86.4 (s); MS (ES+) (0.06 g, 0.90 mmol) and ethanol (2 mL) gave 4-ethoxy-3-
m/z: 290 ( [MH]+, 100%).
fluoro-9,10-dioxa-1,2-diaza-anthracene (9c) (0.07 g, 66%), as
white crystals; mp 131–133 °C; Anal Calcd for C12H9FN2O3:
C, 58.1; H, 3.7; N, 11.3%. Found: C, 58.0; H, 3.7; N, 11.2.
1H NMR (500 MHz, CDCl3, δH): 1.49 (3H, t, 3JHH = 7.0 Hz,
CH3), 4.52 (2H, qd, 3JHH = 7.0 Hz, 5JHF = 1.4 Hz, OCH2),
7.00–7.11 (4H, m, ArH); 13C NMR (125 MHz, DMSO-d6, δC):
Reaction of 3,4-difluoro-9,10-dioxa-1,2-diaza-
anthracene (5) with allylamine
4-Allylamino-3-fluoro-9,10-dioxa-1,2-diaza-anthra-
cene (9b)
Using the procedure described above, 3,4-difluoro-9,10-dioxa- 15.7 (s, CH3), 70.6 (d, 4JCF = 3.9 Hz, OCH2), 116.7 (s, C-5),
1,2-diaza-anthracene (5) (0.15 g, 0.67 mmol), allylamine 117.8 (s, C-6), 125.4 (s, C-7), 126.1 (s, C-8), 133.6 (d, 2JCF =
(0.10 mL, 1.35 mmol) and acetonitrile (2 mL) gave 27.2 Hz, C-4), 135.1 (d, 3JCF = 8.2 Hz, C-4a), 139.2 (s, C-8a),
4-allylamino-3-fluoro-9,10-dioxa-1,2-diaza-anthracene (9b) 140.7 (s, C-10a), 154.0 (d, 4JCF = 1.5 Hz, C-9a), 158.2 (d,
(0.14 g, 80%) as white crystals; mp 175–177 °C; Anal Calcd for 1JCF = 239.5 Hz, C-3); 19F NMR (470 MHz, CDCl3, δF) −92.4
C13H10FN3O2: C, 60.2; H, 3.9; N, 16.2%. Found: C, 60.3; H, (s); MS (ES+) m/z: (249 ([MH]+), 100%).
4.0; N, 16.3. 1H NMR (500 MHz, DMSO-d6, δH): 4.04 (2H, t,
3JHH = 5.1 Hz, NCH2), 5.10 (1H, dd, 3JHH = 10.3 Hz, 2JHH =
Supporting Information
1.5 Hz, =CH2), 5.17 (1H, dd, 3JHH = 17.2 Hz, 2JHH = 1.5 Hz,
=CH2), 5.94 (1H, ddt, 3JHH = 17.2 Hz, 10.2, 5.1, -CH=), 6.96
Supporting Information with 1H NMR and 13C NMR
(1H, br t, 3JHH = 5.1 Hz, NH), 7.07 (3H, m, ArH), 7.12 (1H, m,
spectra for 3,4,6-trifluoro-5-phenoxypyridazine (7),
ArH); 13C NMR (125 MHz, DMSO-d6, δC): 45.7 (d, 4JCF =
1H NMR, 13C NMR and 19F NMR spectra for
2.5 Hz, NCH2), 115.3 (s, =CH2), 116.4 (s, C-5), 117.0 (s, C-6),
3,6-difluoro-4,5-diphenoxypyridazine (8),
124.6 (d, 2JCF = 28.2 Hz, C-4), 125.1 (s, C-7), 125.2 (s, C-8),
3,4-difluoro-9,10-dioxa-1,2-diaza-anthracene (5),
127.2 (d, 3JCF = 9.6 Hz, C-4a), 136.1 (s, CH=), 139.4 (s, C-8a),
3-fluoro-4-(morpholin-4-yl)-9,10-dioxa-1,2-diaza-anthrace
140.5 (s, C-10a), 152.3 (s, C-9a), 155.2 (d, 1JCF = 230.4 Hz,
ne (9a),
C-3); 19F NMR (470 MHz, DMSO-d6, δF) −93.7 (s); MS (ES+)
4-allylamino-3-fluoro-9,10-dioxa-1,2-diaza-anthracene
m/z: 323 ([M+MeCN+Na]+, 100%), 260 ([MH]+, 68), 219 (69).
(9b), 4-ethoxy-3-fluoro-9,10-dioxa-1,2-diaza-anthracene
(9c).
Crystal data for 9b: C13H10FN3O2, M = 259.24, monoclinic,
Supporting Information File 1
NMR spectra of all synthesized compounds 7, 8, 5 and
9a–9c
space group P21/n, a = 4.9065(1), b = 19.5663(4), c =
11.8180(2) Å, β = 94.25(1)°, U = 1131.44(4) Å3, F(000) = 536,
Z = 4, Dc = 1.5220 mg·m−3, μ = 0.117 mm−1 (Mo Kα, λ =
0.71073 Å), T = 120.0(2) K. 14166 reflections were collected
on a Bruker SMART 6000 diffractometer (ω-scan, 0.3°/frame)
yielding 2875 unique data (Rmerg = 0.0615). The structure was
solved by direct method and refined by full-matrix least squares
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-6-45-S1.pdf]
on F2 for all data using Olex2 software. All non-hydrogen Acknowledgements
atoms were refined with anisotropic displacement parameters, We thank GlaxoSmithKline and EPSRC for funding (student-
H-atoms were located on the difference map and refined ship to GP).
isotropically. Final wR2(F2) = 0.1275 for all data (212 refined
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