Domino reaction for the construction of new 2-oxo[1,2,4]triazolo[5,1- c][1,4]thiazines

Article abstract of DOI:10.1055/s-0028-1087928

The synthesis of highly functionalized α-thiohydrazones by Michael addition of 3-mercapto-2-ketones to 1,2-diazabuta-1,3-dienes is described. The phosphorylated α-thiohydrazones were hydrolyzed into β-ketophosphine oxides or phosphonates containing a merc

Full text of DOI:10.1055/s-0028-1087928

LETTER
735
Domino Reaction for the Construction of New 2-Oxo[1,2,4]triazolo[5,1-
c][1,4]thiazines
N
ew 2-Oxo[1,2, 4]
r
triazolo[
a
5, 1-
c
]
[1,4]th
z
iazine
s
io A. Attanasi,a Samuele Lillini,a Fabio Mantellini,*a Jesús M. de los Santos,b Roberto Ignacio,b Francisco
Palacios*b
a
Istituto di Chimica Organica, Università degli Studi di Urbino ‘Carlo Bo’, Via I Maggetti 24, 61029 Urbino (PU), Italy
Departamento de Química Orgánica I, Facultad de Farmacia, Universidad del País Vasco, Apartado 450, 01080 Vitoria, Spain
b
Fax +39(0722)303441; E-mail: fabio.mantellini@uniurb.it
Received 17 November 2008
diazabuta-1,3-dienes 1a–i containing a phosphine oxide, a
phosphonyl or a carboxylate group in position 4 at room
temperature, in dichloromethane in the case of 1a,b,i or in
acetonitrile in the case of 1c–h (Scheme 1). The nucleo-
Abstract: The synthesis of highly functionalized a-thiohydrazones
by Michael addition of 3-mercapto-2-ketones to 1,2-diazabuta-1,3-
dienes is described. The phosphorylated a-thiohydrazones were hy-
drolyzed into b-ketophosphine oxides or phosphonates containing a
mercapto ketone in the a position, while the a-thiohydrazones with philic attack of the mercapto group of 2 at the terminal
a carboxylate group were subsequently transformed into 2-oxo-
carbon of the heterodiene system of 1,2-diazabuta-1,3-
2,3,8,8a-tetrahydro-1H-[1,2,4]triazolo[5,1-c][1,4]thiazines by means
of a domino reaction.
dienes 1 led to a-sulfur hydrazone 1,4-adducts 3a–m, iso-
lated by chromatography on silica in excellent yields
(Table 1).19
Key words: 1,2-diazabuta-1,3-dienes, [1,4]thiazines, [1,2,4]triaz-
ol-2-ones, Michael addition, domino reaction.
O
O
O
O
PR2
PR2
S
SH
Heterocycles containing nitrogen and sulfur possess im-
portant biological activities. For instance, the thiazine
substructure exhibits sedative,1 neuroleptic,2 antitussive,3
antipsoriatic,4 anti-HIV,5 antifungal, anti-inflammatory
and anthelminthic6 activities. Derivatives of [1,4]thiazine
act as myocardial calcium channel modulators7 and also
as a vasopressin receptor antagonist.8 On the other hand,
the triazolone ring structure is found in a number of bio-
logically active compounds, including antifungals,9 anti-
inflammatories,10 antitumor agents,11 PPARs agonists,12
and NK1 antagonists.13 Hence, it was considered of inter-
est to synthesize novel14 structures containing these two
fused rings.
R4
R4
R2
O
R2
O
4a–e
2
5
R1 = POR2
R4
ii
R1
R1
S
H
O
COR3
R2
N
i
SH
N
O
N
R2
+
NH
R4
2a,b
R3OC
3a–m
1a–i
R1 = COOR
R3 = NH2
R1 = COOR
R3 = NH2
iii
i, ii
To the best of our knowledge, few simple methods for the
synthesis of 2,3-substituted 5,6-dihydro-4H-1,4-thiazines
from readily available starting materials are reported in
the chemical literature.14,15 The most common ones em-
ploy 2-aminoethanethiol in a [4+2]-cyclization with a-ha-
logenated carbonylic compounds16 or with allenic
structures.17 Recently we have shown that the reaction be-
tween 2-aminoethanethiol and 1,2-diazabuta-1,3-dienes
first furnishes the hydrazone 1,4-adduct (Michael-type)
by means of nucleophilic attack of the sulfur at the hetero-
diene system. The amino group of the parent 2-amino-
ethanethiol subsequently gives rise to an internal
nucleophilic attack at the carbon of the hydrazono group
with formation of the [1,4]thiazine core.18
R4
S
R1
R2
R4
S
R1
N
HO
N
R2
HN
O
NH
H2N
NH
O
7a–h
6
Scheme 1 Synthesis of a-thiohydrazone 1,4-adducts 3a–m, mercapto
diketones 4a–e and 8,8a-dimethyl-2-oxo-2,3,8,8a-tetrahydro-1H-
[1,2,4]triazolo[5,1-c][1,4]thiazine-6-carboxylate derivatives 7a–h.
Reagents and conditions: (i) CH2Cl2, r.t. for 1a,b,i; MeCN, r.t. for 1c–
h; (ii) MeCN, r.t., Amberlyst 15H for 3a,b,k–m; (iii) MeCN, reflux,
Amberlyst 15H for 3c; MeCN, reflux for 3d–j.
Herein we report the addition of 3-mercaptobutan-2-one
2a or 3-mercaptopentan-2-one 2b to functionalized 1,2-
In the presence of Amberlyst 15H, the hydrazono double
bond of phosphorylated hydrazones 3a,b and 3k–m was
readily hydrolyzed in acetonitrile at room temperature to
give functionalized mercapto diketones 4a–e in good
SYNLETT 2009, No. 5, pp 0735–0738
x
x.
x
x.
2
0
0
9
Advanced online publication: 24.02.2009
DOI: 10.1055/s-0028-1087928; Art ID: D38908ST
© Georg Thieme Verlag Stuttgart · New York

736
O. A. Attanasi et al.
LETTER
Table 1 Yields of a-Thiohydrazones 3a–m, Functionalized Mercapto Diketones 4a–e, and 2-Oxo[1,2,4]triazolo[5,1-c][1,4]thiazines 7a–h
1
R1
R2
R3
2
R4
3
Yield (%)a
4
Yield (%)b
7
Yield (%)a Yield (%)b
1a
1b
1c
1d
1e
1f
POPh2
Me
Me
Me
Et
OEt
OEt
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
OEt
OEt
NH2
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2b
Me
Me
Me
Me
Me
Me
Me
Et
3a
3b
3c
3d
3e
3f
97
94
89
91
96
87
90
98
97
98
81
70
97
4a
4b
85
88
PO(OEt)2
CO2Me
CO2Me
CO2Et
7a
7b
7c
7d
7e
7f
31
32
40
38
35
36
31
39
34
41
37
35
32
31
34
Me
Me
Me
Me
Me
Me
Me
Me
Et
CO2i-Pr
CO2Allyl
CO2Et
1g
1e
1f
3g
3h
3i
CO2i-Pr
CO2Bn
POPh2
Et
7g
7h
1h
1a
1b
1i
Et
3j
Et
3k
3l
4c
4d
4e
67
87
60
PO(OEt)2
POPh2
Et
Et
3m
a Yield of isolated purified compounds 3a–m and 7b–h based on 1,2-diazabuta-1,3-dienes 1.
b Yield of isolated purified compounds 4a–e and 7a–h based on hydrazones 3.
yields (Scheme 1, Table 1).20 As far as we know,14 these hydroxy group by the ureidic nitrogen produces com-
functionalized b-ketophosphine oxides or phosphonates pounds 7 through a further ring closure process.
containing a mercapto ketone in the a position are de-
We have also performed the reaction between 1d–h and
2a,b in one pot without the isolation of the hydrazone in-
termediates 3d–j (Table 1). In this case, the reaction is
carried out at room temperature until disappearance of
1,2-diazabuta-1,3-dienes 1d–h, as evidenced by the disap-
pearance of the typical red color. The mixture is then di-
rectly refluxed in order to obtain the final products 7b–h.
To the best of our knowledge, this simple strategy repre-
sents the first direct access to widely substituted 2-
oxo[1,2,4]triazolo[5,1-c][1,4]thiazines. Bicyclic [1,4]thi-
azine 1,2,4-triazol-3-one and 1,2,4-triazol-3-one deriva-
tives analogous to compound 7 are known as peripheral 5-
HT2 antagonists. Moreover this kind of compound has
shown a1-adrenoceptor antagonist activity which has been
scribed for the first time and could be interesting sub-
strates for the preparation of acyclic and cyclic
derivatives.21 Taking into account that hydrazones are the
starting material for the preparation of 1,2-diazabuta-1,3-
dienes 1a,b,i and that hydrazones can be considered as
protected carbonyl compounds, with this strategy it could
be possible to reverse the polarity (umpolung reaction) of
the a-carbon atom of the carbonyl group and/or of the
phosphine oxide (phosphonate) group22 of b-ketophos-
phine oxides 5 (R = Ph) or phosphonates 5 (R = OEt) fa-
voring the introduction of a nucleophilic reagent
(mercaptano ketone) in order to prepare the functionalized
carbonyl derivatives (see Scheme 1).
Under the same reaction conditions, carboxylated hydra- confirmed to be responsible for blood pressure reduc-
zones 3c–j surprisingly furnished new and interesting tion.24
8,8a-dimethyl-2-oxo-2,3,8,8a-tetrahydro-1H-[1,2,4]triaz-
In conclusion, this paper describes a simple procedure to
prepare a-thiohydrazones or functionalized mercapto
diketones and offers a straightforward access to new 2-
oxo[1,2,4]triazolo[5,1-c][1,4]thiazines. The synthesis
proceeds under mild conditions and utilizes readily avail-
olo[5,1-c][1,4]thiazine-6-carboxylate derivatives 7a–h
(Scheme 1, Table 1) by means of a domino reaction.23 The
first step of this process is the intramolecular nucleophilic
attack of the hydrazone nitrogen at the ketone moiety with
the formation of nonisolable 4-[(aminocarbonyl)amino]-
able starting materials. Furthermore, the present investi-
3-hydroxy-3,4-dihydro-2H-1,4-thiazine-6-carboxylate inter-
gations demonstrate once again the usefulness of 1,2-
diazabuta-1,3-dienes as building blocks in organic chem-
mediates 6. It is noteworthy that the nitrogen involved in
the formation of the thiazine ring is derived from 1,2-
istry.25
diazabuta-1,3-dienes
unlike
in
our
previous
communication18 and many classical synthesis in which
the nitrogen is furnished from an aminothiol deriva-
tive.16,17 The subsequent nucleophilic substitution of the
Acknowledgment
The Italian authors thank the Ministero dell’Università, dell’Istru-
zione e della Ricerca (MIUR)-Roma and the Università degli Studi
Synlett 2009, No. 5, 735–738 © Thieme Stuttgart · New York

LETTER
New 2-Oxo[1,2,4]triazolo[5,1-c][1,4]thiazines
737
di Urbino ‘Carlo Bo’ and the Spanish authors thank the Departa-
mento de Educación Universidades e Investigación del Gobierno
Vasco (IT 277- 07) and the Dirección General de Investigación del
Ministerio de Ciencia y Tecnología (MCYT, Madrid DGI,
CTQ2006-09323) for financial support.
amount of 1,2-diazabuta-1,3-dienes 1c–h (1.0 mmol) as a
mixture of E/Z isomers26 was added to a solution of 3-
mercaptobutan-2-one 2a (1.1 mmol) or 3-mercaptopentan-2-
one 2b (1.1 mmol) in MeCN (20 mL) with magnetic stirring
at r.t. The reactions were allowed to stand under these
conditions for 2 h until the complete disappearance of the
starting materials (monitored by TLC). The reaction solvent
was then evaporated under reduced pressure and products
3c–j were purified by flash column chromatography (silica
gel, EtOAc).
References and Notes
(1) Iwahara, S.; Iwasaki, T.; Hasegawa, Y.
Psychopharmacologia 1968, 13, 341.
Ethyl 2-(Diphenylphosphoryl)-1-methyl-2-[(1-methyl-2-
oxopropyl)sulfanyl]ethylidene-1-hydrazinecarboxylate
(3a): yield: 433 mg (97%); obtained as a colorless solid as
described in the general procedure; mp 143–145 °C. IR
(KBr): 3457, 3195, 2978, 1733, 1533, 1436, 1236, 1042 cm–
1. 1H NMR (400 MHz, CDCl3): d = 1.19–1.23 (m, 6 H), 1.82
(s, 3 H), 1.90 (d, 3 H, 4JPH = 1.1 Hz, major), 1.91 (d, 3 H, 4JPH
= 1.1 Hz, minor), 3.34 (q, 1 H, 3JHH = 7.2 Hz, major), 3.40
(q, 1 H, 3JHH = 6.8 Hz, minor), 4.19–4.22 (m, 2 H), 4.39 (d,
1 H, 2JPH = 10.0 Hz), 4.42 (d, 1 H, 2JPH = 9.6 Hz), 7.41–7.88
(m, 10 H). 13C NMR (75 MHz, CDCl3): d = 13.4, 13.6, 14.4,
14.4, 16.1, 16.2, 25.1, 26.7, 48.7 (d, 3JPC = 6.5 Hz), 49.4 (d,
3JPC = 6.0 Hz), 52.1 (d, 1JPC = 65.5 Hz), 52.6 (d, 1JPC = 66.1
Hz), 61.7, 128.1, 128.2, 128.2, 128.3, 128.4, 128.6, 129.4,
130.0, 130.4, 130.6, 130.7, 130.7, 130.9, 131.0, 131.1,
131.1, 131.2, 131.2, 131.3, 131.4, 131.9, 131.9, 147.6,
148.4, 153.6, 204.4, 204.7. 31P NMR (120 MHz, CDCl3): d
= 28.1 (major), 28.4 (minor). HRMS: m/z [M+] calcd for
C22H27N2O4PS: 446.1429; found: 446.1434.
(2) Oelssner, W. Jr.; Peinhardt, G.; Buge, A. Pharmazie 1985,
40, 320.
(3) Parish, F. A. Med. Times 1959, 87, 1488.
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2004, 47, 1930.
(5) Arranz, M. E.; Diaz, J. A.; Ingate, S. T.; Witvrouw, M.;
Pannecouque, C.; Balzarini, J.; De Clercq, E.; Vega, S.
Bioorg. Med. Chem. 1999, 45, 3475.
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D.; Chiarini, A. J. Med. Chem. 2002, 45, 3475.
(8) Galanski, M. E.; Erker, T.; Handler, N.; Lemmens-Gruber,
R.; Kamyar, M.; Studenik, C. R. Bioorg. Med. Chem. 2006,
14, 826.
(9) Heers, J.; Backx, J. J.; Cutsem, J. V. J. Med. Chem. 1984, 27,
894.
(10) Mullican, M. D.; Wilson, M. W.; Connor, D. T.; Kostlan,
C. R.; Schrier, D. J.; Dyer, D. D. J. Med. Chem. 1993, 36,
1090.
(20) General Procedure for the Synthesis of Mercapto
Diketones 4a–e: To a solution of the a-thiohydrazone
3a,b,k,l,m (1.0 mmol) in MeCN (5 mL), Amberlyst 15H
ion-exchange resin (50 mg) was added. The reaction was
stirred at r.t. for 2 h. The solid was then filtered through a
sintered glass vacuum filtration funnel. The filtrate was
concentrated to dryness in vacuum. The crude products were
purified by flash column chromatography (silica gel,
EtOAc) to afford the corresponding mercapto diketones
4a–e.
(11) Neslihan, D.; Reyhan, U.; Ahmet, D. Bioorg. Med. Chem.
2002, 10, 3717.
(12) Xu, Y.; Mayhugh, D.; Saeed, A.; Wang, X.; Thompson,
R. C.; Dominianni, S. J.; Kauffman, R. F.; Sing, J.; Bean,
J. S.; Bensch, W. R.; Barr, R. J.; Osborne, J.; Montrose-
Rafizadeh, C.; Zink, R. W.; Yumibe, N. P.; Huang, N.;
Luffer-Atllas, D.; Rungta, D.; Maise, D. E.; Mantlo, N. B.
J. Med. Chem. 2003, 46, 5121.
(13) Cowden, C. J.; Wison, R. D.; Bishop, B. C.; Cottrel, I. F.;
Davies, A. J.; Dollong, U. Tetrahedron Lett. 2000, 41, 8661.
(14) SciFinder Scholar, CAS; American Chemical Society:
Columbus OH, 2006.
(15) Aitken, R. A. In Comprehensive Heterocyclic Chemistry III,
Vol. 8; Katritzky, A. R., Ed.; Elsevier: Oxford, 2008.
(16) For some recent applications, see: (a) Dixon, S.; Wang, X.;
Lam, K. S.; Kurth, M. J. Tetrahedron Lett. 2005, 46, 7443.
(b) Freed, J. D.; Hart, D. J.; Magomedov, N. A. J. Org.
Chem. 2001, 66, 839.
(17) Landor, S. R.; Landor, P. D.; Seliki-Muruumu, J.; Fomum,
Z. T.; Mbafor, J. T. J. Chem. Soc., Perkin Trans. 1 1998,
1759.
3-[1-(Diphenylphosphoryl)-2-oxopropyl]sulfanylbutan-
2-one (4a): isomeric mixture of the keto and enol tautomers;
yield: 306 mg (85%); obtained as a colorless oil as described
in the general procedure. IR (film): 3435, 3046, 2921, 1705,
1431, 1362, 1197, 1117 cm–1. 1H NMR (300 MHz, CDCl3):
d = 0.94 (d, 3 H, 3JHH = 7.2 Hz), 1.24 (d, 3 H, 3JHH = 7.2 Hz),
1.82 (s, 3 H), 1.91 (s, 3 H), 1.96 (s, 3 H), 2.37 (s, 3 H), 2.39
(s, 3 H), 3.31 (q, 1 H, 3JHH = 7.2 Hz), 4.12 (d, 1 H, 2JPH = 12.0
Hz), 4.15 (d, 1 H, 2JPH = 11.1 Hz), 7.55–7.92 (m, 10 H). 13
C
NMR (75 MHz, CDCl3): d = 15.1, 15.3, 21.1 (d, 3JPC = 6.1
Hz), 24.6, 26.2, 26.7, 29.4, 48.6 (d, 3JPC = 5.5 Hz), 48.7 (d,
3JPC = 5.5 Hz), 52.5, 54.0 (d, 1JPC = 45.1 Hz), 54.7 (d, 1JPC
45.5 Hz), 82.1 (d, 1JPC = 108.7 Hz), 128.2, 128.3, 128.5,
128.5, 128.6, 128.7, 131.1, 131.2, 131.2, 131.3, 131.4,
131.4, 131.5, 132.0, 132.2, 132.3, 132.3, 132.4, 132.5,
132.5, 132.6, 186.5 (d, 2JPC = 12.7 Hz), 200.8, 202.2, 203.6,
204.3, 205.9. 31P NMR (120 MHz, CDCl3):
=
(18) Attanasi, O. A.; Filippone, P.; Lillini, S.; Mantellini, F.;
Nicolini, S.; de los Santos, J. M.; Ignacio, R.; Aparicio, D.;
Palacios, F. Tetrahedron 2008, 64, 9264.
(19) General Procedure for the Synthesis of a-Thiohydrazone
1,4-Adducts 3a–m: To an ice-cooled solution of 1,2-
diazabuta-1,3-diene 1a,b,i as a mixture of E/Z isomers (1.0
mmol) in CH2Cl2 (5 mL), the 3-mercaptobutan-2-one 2a (1.1
mmol) or 3-mercaptopentan-2-one 2b (1.1 mmol) was
added. The reaction was allowed to stir at r.t. for 4 h. The
solvent was removed by rotary evaporation and the crude
products were purified by crystallization for compound 3m
or by flash column chromatography (silica gel, EtOAc) for
compounds 3a,b,k,l to afford a-thiohydrazone 1,4-adducts
derived from phosphine oxide and phosphonate-substituted
1,2-diazabuta-1,3-dienes. To obtain 3c–j, a stoichiometric
d = 26.8, 27.7, 41.4. HRMS: m/z [M+] calcd for C19H21O3PS:
360.0949; found: 360.0952.
(21) (a) Palacios, F.; Alonso, C.; de los Santos, J. M. Chem. Rev.
2005, 105, 899. (b) Moonen, K.; Laureyn, I.; Stevens, C. V.
Chem. Rev. 2004, 104, 6177.
(22) Palacios, F.; Aparicio, D.; López, Y.; de los Santos, J. M.
Tetrahedron 2005, 61, 2815.
(23) General Procedure for the Synthesis of
[1,2,4]Triazolo[5,1-c][1,4]thiazines 7a–h: To obtain
[1,2,4]triazolo[5,1-c][1,4]thiazines 7b–h, the a-thiohydra-
zones 3d–j (1 mmol) were refluxed in MeCN for 26–48 h.
Synlett 2009, No. 5, 735–738 © Thieme Stuttgart · New York

738
O. A. Attanasi et al.
LETTER
(25) For some recent developments, see: (a) Attanasi, O. A.;
To prepare compounds 7b–h directly, a stoichiometric
amount of 1,2-diazabuta-1,3-dienes 1d–h (1 mmol) was
added to a solution of 3-mercaptobutan-2-one 2a (1.1 mmol)
or 3-mercaptopentan-2-one 2a (1.1 mmol) in MeCN (20 mL)
with magnetic stirring at r.t. until the disappearance of the
reagent, as evidenced by disappearance of typical red color
of the 1,2-diazabuta-1,3-dienes 1. The crude was then
refluxed for 26–48 h. In the case of 7a the hydrazone 3c (1
mmol) was refluxed for 28 h in the presence of a
stoichiometric amount of Amberlyst 15H ion-exchange resin
(1 mmol). After disappearance of the starting materials
(monitored by TLC), the reaction solvent was evaporated
under reduced pressure and products 7a–h were purified by
flash column chromatography (silica gel; EtOAc–cyclo-
hexane, 50:50).
Methyl 5,8,8a-Trimethyl-2-oxo-2,3,8,8a-tetrahydro-1H-
[1,2,4]triazolo[5,1-c][1,4]thiazine-6-carboxylate (7a):
yield: 72 mg (31%); obtained as a blue oil as described in the
general procedure. IR (nujol): 3243, 1753, 1712, 1643 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 1.22 (d, 3 H, 3J = 6.4
Hz), 1.39 (s, 3 H), 2.37 (s, 3 H), 2.58 (q, 1 H, 3J = 6.4 Hz),
3.56 (s, 3 H), 8.38 (s, 1 H), 9.15 (s, 1 H). 13C NMR (100
MHz, DMSO-d6): d = 13.5 (q), 17.1 (q), 22.2 (q), 40.8 (d),
51.0 (q), 83.1 (s), 87.6 (s), 149.0 (s), 159.4 (s), 165.0 (s). MS:
m/z (%) = 257 (96)[M+], 225 (100), 197 (67), 166 (57), 139
(81), 108 (16). Anal. Calcd for C10H15N3O3S: C, 46.68; H,
5.88; N, 16.33. Found: C, 46.82; H, 5.92; N, 16.19.
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