Symmetrical spiro-phosphoroheterocycles from the selenation of carbohydrazides

Article abstract of DOI:10.1016/j.tetlet.2011.04.058

2,4-Bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide (Woollins' reagent) reacts with benzoic hydrazides in refluxing toluene to give new symmetrical spiro heterocycles in 48-76% isolated yields. However, under identical conditions, treating Woollins' reagent with thiophene-2-carbohydrazide leads to an additional product, 1,3,4-selenadiazole (27% yield) together with the spiro phosphorus heterocycle in 44% yield. Three representative X-ray structures are reported.

Full text of DOI:10.1016/j.tetlet.2011.04.058

Tetrahedron Letters 52 (2011) 3311–3314
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Symmetrical spiro-phosphoroheterocycles from the selenation
of carbohydrazides
⇑
Guoxiong Hua, David B. Cordes, Yang Li, Alexandra M. Z. Slawin, J. Derek Woollins
School of Chemistry, University of St. Andrews, Fife KY16 9ST, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
2,4-Bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide (Woollins’ reagent) reacts with benzoic
hydrazides in refluxing toluene to give new symmetrical spiro heterocycles in 48–76% isolated yields.
However, under identical conditions, treating Woollins’ reagent with thiophene-2-carbohydrazide leads
to an additional product, 1,3,4-selenadiazole (27% yield) together with the spiro phosphorus heterocycle
in 44% yield. Three representative X-ray structures are reported.
Received 24 March 2011
Revised 4 April 2011
Accepted 15 April 2011
Available online 23 April 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Phosphorus
Selenium
Heterocycle
Woollins’ reagent
X-ray structure
Spiro compounds
Phosphorus-containing heterocycles continue to attract consid-
erable attention, in part due to their large variety of interesting phar-
macological and biological activities, such as herbicidal, insecticidal,
antibacterial, antifungal and anticancer.1–4 2,4-Bis(phenyl)-1,3-
Woollins’ reagent leads to 2,5-disubstituted 1,3,4-selenadiazoles10
and so the formation of 5 is not surprising.
A possible reaction pathway for the formation of compounds 1–
4 and 6 proceeds via two step-wise nucleophilic substitutions in
which the selenium atoms in Woollins’ reagent are replaced twice
by nitrogen and oxygen atoms from the carbohydrazide. The lack
of selenation of the carbonyl group suggests that the hydrazide at-
tacks phosphorus through nitrogen first, rather than through the
carbonyl oxygen. At elevated temperatures WR is believed to be
in equilibrium with a diselenaphosphorane (PhPSe2) intermediate
A, which can be considered to be the reactive species in refluxing
solution. First, the reaction of A with one molecule of carbohydraz-
ide affords intermediate B via a nucleophilic substitution followed
by an intramolecular proton transfer. Intermediate C (the tautomer
of intermediate B) cyclizes and loses a molecule of H2Se to afford D,
which undergoes another nucleophilic substitution with a second
molecule of carbohydrazide, followed by an intramolecular proton
transfer to generate E. Intermediate F (the tautomer of intermedi-
ate E) cyclizes by eliminating a molecule of H2Se to give stable
compounds 1–4 or 6 (Scheme 3).
diselenadiphosphetane-2,4-diselenide [{PhP(Se)(l-Se)}2, Woollins’
reagent (WR)] has become a very useful selenium source or
selenation reagent in synthetic chemistry5–15 because of its ready
preparation and ease of handling.16 As part of our studies aimed at
the reactivity of Woollins’ reagent towards different organic
substrates, herein, we report the preparation of a series of novel
spiro organophosphorus heterocycles via the selenation of carbohy-
drazides with Woollins’ reagent.
Woollins’ reagent reacted with 2 equiv of benzohydrazides in
refluxing toluene for 4 h. During this period the red suspension
gradually disappeared and a pale yellow solution was formed with
precipitation of small amounts of grey elemental selenium. Upon
cooling to room temperature the solution was passed through a
silica gel column. The fractions containing the product were
combined and concentrated in vacuum to give the air- and mois-
ture-stable compounds 1–4 in 48–76% isolated yields (Scheme 1).
Interestingly, treating Woollins’ reagent with 2 equiv of
thiophene-2-carbohydrazide under identical conditions led to
1,3,4-selenadiazole 5 in 27% yield along with spiro phosphorus
heterocycle 6 in 44% yield after work-up in air (Scheme 2). We
have previously noted that reaction of 1,2 diacylhydrazines with
Reaction of Woollins’ reagent with one equimolar equivalent of
benzohydrazine was performed under identical conditions to
investigate if intermediate D could be isolated or was stable.
Unfortunately, the same compounds 1–4 and 6 were isolated as
the only products with much lower yields (ca. 25–35%) rather than
intermediate D.
The release of H2Se in the above reactions was observed in the
bubbler (the formation of dark Se due to the decomposition of the
⇑
Corresponding author. Tel.: +44 1334 463384.
E-mail address: jdw3@st-and.ac.uk (J. Derek Woollins).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.058

3312
G. Hua et al. / Tetrahedron Letters 52 (2011) 3311–3314
Se
Ph
Se
Se
Ph
P
P
NH
P
N
Se
WR
O
C
O
R
R
NHNH2
R
toluene, reflux, 4 h
O
N
HN
1 R = H, 48% 2 R = Br, 58%
3 R = CH3, 54% 4 R = NO2, 76%
Scheme 1. Formation of spiro phosphorus heterocycles 1–4 from the selenation of benzohydrazines.
Se
Ph
Se
Se
P
P
O
C
N
NH
P
Se
WR
Ph
N
N
S
S
O
+
NHNH2
O
S
toluene, reflux, 4 h
Se
S
S
N
HN
5
6
Scheme 2. Formation of compounds 5 and 6 from the selenation of thiophene-2-carbohydrazide.
O
Ar
Ar
Ar
Se
C
NH NH2
N
C
C
NH
Se
Se
Se
Ph
Se
NH
NH
H transfer
O
HO
SeH
SeH
P
Ph
P
P
P
Ph
N
P
Ph
Se
WR
Ph
Se
Se
A
B
C
Ar
Ar
H2Se
HO
O
C
C
O
C
NH
P
N
NH
N
Ar
NHNH2
NH
P
NH
N
Se
Ph
P
N
H
N
H
H transfer
Ar
Ar
O
O
O
Ar
SeH
Ph
Ph
SeH
Cyclization
H2Se
E
D
F
N
NH
Ar
O
P
Ar
O
HN
1-4 and 6
N
Ph
Scheme 3. Possible reaction pathway for the formation of compounds 1–4 and 6.
H2Se) and could be trapped by sodium hydroxide as sodium sele-
nate (NaSeO4) after the bubbler.
35.0 ppm support the proposed formulation of these spiro hetero-
cyclic systems. For 5, the m(C
@
vibrations were observed at 1449
N)
The proposed structures of 1–6 are based on their spectral anal-
ysis and accurate mass measurement. Compounds 3, 5 and 6 were
further characterised by single crystal X-ray structure determina-
tion. Compounds 1–6 are stable to air and moisture for several
months without any apparent visible decomposition. All com-
pounds showed the anticipated [M]+ or [M+H]+ peak in their mass
spectra. The IR spectra of compounds 1–4 and 6 displayed m(C@N)
and 1406 cmÀ1. The presence of the typical 13C NMR signal at
164.1 ppm for the C@N double bond and 77Se NMR signal at
689.6 ppm (similar to related structures10) confirmed the forma-
tion of the five-membered C–N–N–C–Se ring.
Compounds 3, 5 and 6 were crystallized by slow diffusion of
dichloromethane solutions into hexane to give colourless crystals
of 3 and 6, and brown crystals of 5. The X-ray structures of 3 and
6 (Figs. 1 and 2) confirm the presence of the spiro heterocyclic rings,
best described as existing in a ‘T’ stage conformation. The two newly
formed phosphorus–nitrogen heterocycles in 3 or 6 have symmetri-
cal (6) or near-symmetrical (3) configuration about the
phosphorus–phenyl ring axis. Each phosphoroheterocycle is
almost co-planar with the toluene ring or furan ring, the two rings
vibrations in the range of 1397–1485 cmÀ1, with
of 1054–1097 cmÀ1 and
m
(P–O) in the range
m
(P–N) in the range of 660–710 cmÀ1 being
comparable with related heterocycles.17,18 The absence of m(C@O)
(1599–1637 cmÀ1) and the presence of the typical 13C NMR signals
in the range of 142.2–164.6 ppm for the C@N double bond and the
31P NMR spectra comprising only a singlet in the range of À37.1 to

G. Hua et al. / Tetrahedron Letters 52 (2011) 3311–3314
3313
Figure 3. Single crystal X-ray structure of compound 5 (hydrogen atoms omitted
for clarity). Selected bond lengths (Å) and angles (°) (esds in parentheses): Se(1)–
C(1) 1.881(8), Se(1)–C(11) 1.876(8), C(1)–N(1) 1.314(10), C(11)–N(11) 1.300(10),
N(1)–N(11) 1.372(9); C(1)–Se(1)–C(11) 81.9(4), Se(1)–C(1)–N(1) 113.6(6), Se(1)–
C(11)–N(11) 115.2(7), C(1)–N(1)–N(11) 115.4(7), C(11)–N(11)–N(1) 113.9(7).
Figure 1. Single crystal X-ray structure of compound 3 (hydrogen atoms bound to
carbon omitted for clarity). Selected bond lengths (Å) and angles (°) (esds in
parentheses): P(1)–N(1) 1.652(4), P(1)–N(11) 1.650(4), P(1)–O(1) 1.739(2), P(1)–
O(11) 1.720(2), O(1)–C(1) 1.355(5), O(11)–C(11) 1.356(5), C(1)–N(2) 1.309(5),
C(11)–N(12) 1.288(5), N(1)–N(2) 1.398(4), N(11)–N(12) 1.403(4); N(1)–P(1)–N(11)
128.74(16), N(1)–P(1)–O(1) 86.51(15), N(11)–P(1)–O(11) 86.56(16), O(1)–P(1)–
O(11) 172.05(11), C(1)–O(1)–P(1) 111.1(2), C(11)–O(11)–P(1) 111.9(2), N(12)–
N(11)–P(1) 117.6(3), N(2)–N(1)–P(1) 118.3(3), N(2)–C(1)–O(1) 117.2(3), N(12)–
C(11)–O(11) 116.6(3), C(1)–N(2)–N(1) 106.3(3), C(11)–N(12)–N(11) 107.3(3).
The X-ray structure of 5 (Fig. 3) shows the formation of a new
five-membered ring compound,
a
bis-thiophene-substituted
1,3,4-selenadiazole. The C2N2Se ring is approximately co-planar
with the two thiophene substituents, with angles between the
ring-planes of 3.1° and 4.2°. The C–Se bond lengths [1.876(8) and
1.881(8) Å] are similar to those in the 2,5-diarylselenophenes (ca.
1.86–1.89 Å),12 although they are slightly shorter than those ob-
served in related structures containing single C–Se bonds (ca.
1.92–1.94 Å),23,24 indicating a degree of delocalisation. However,
the C–Se–C angle [81.9(4)°] is considerably smaller than those
[ca. 87.7(7)–88.7(10)°] in 2,5-diarylselenophenes.13
In conclusion, the selenation of carbohydrazides to give a series
of new symmetrical spiro-phosphoroheterocycles were effectively
achieved using Woollins’ reagent under mild conditions in moder-
ate to high yields.27
Acknowledgments
Figure 2. Single crystal X-ray structure of compound 6 (hydrogen atoms bound to
carbon, and the minor occupancy form of the disordered thiophene ring omitted for
clarity). Selected bond lengths (Å) and angles (°) (esds in parentheses): P(1)–N(1)
1.653(3), P(1)–O(1) 1.734(3), N(1)–N(2) 1.409(5), O(1)–C(1) 1.332(5), C(1)–N(2)
1.290(5); P(1)–N(1)–N(2) 117.7(3), N(1)–P(1)–N(1A) 128.6(3), N(1)–P(1)–O(1)
86.34(15), O(1)–P(1)–O(1A) 173.1(2), C(1)–O(1)–P(1) 111.2(2), N(2)–C(1)–O(1)
118.6(4), C(1)–N(2)–N(1) 105.8(3).
The authors are grateful to the University of St. Andrews and
the Engineering and Physical Science Research Council (EPSRC,
UK) for financial support.
References and notes
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172.05(11)° in 3, N(1)–P(1)–N(1A) 128.6(3)° and O(1)–P(1)–O(1A)
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nearly planar, and all the phenyl rings project from the same side
of the chain, whereas in 6 the chain adopts a more zigzag form,
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G. Hua et al. / Tetrahedron Letters 52 (2011) 3311–3314
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25. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
HRMS [CI+, m/z]: 298.9220 [M+H]+, calculated mass for C10H7N2S2Se: 298.9216.
Compound 6: 0.171 g as a pale white solid in 44% yield. Mp 202–204 °C.
Selected IR (KBr, cmÀ1): 1610(m), 1527(m), 1439(s), 1360(s), 1349(m),
1323(m), 1054(s), 1027(m), 851(m), 697(s). 1H NMR (CD2Cl2, d), 7.81 (d,
J(H,H) = 6.3 Hz, 2H, Thioph-H), 7.58 (d, J(H,H) = 6.3 Hz, 2H, Thioph-H), 7.42–
7.35 (m, 5H, ArH), 7.19 (d, J(H,H) = 6.3 Hz, 2H, Thioph-H), 7.02 (d, 2H, NH
2J(P,H) = 47 Hz) ppm. 13C NMR (CD2Cl2, d), 157.5 (d, 2J(P,C) = 11.4 Hz, C@N),
131.2, 130.9, 130.3, 129.9, 128.8, 128.7, 128.3, 127.6, 127.5, 127.1, 125.0 ppm.
31P NMR (CD2Cl2, d), À37.1 ppm. MS (EI+, m/z), 388 [M]+, 111 [M-C11H11N4OS]+.
HRMS [CI+, m/z]: 389.0291 [M+H]+, calculated mass for C16H14O2N4PS2:
389.0290.
26. Superflip Palatinus, L.; Chapuis, G. J. Appl. Crystallogr. 2007, 40, 786–790.
27. Compound 1: 0.090 g as a white solid in 48% yield. Mp 240–242 °C. Selected IR
(KBr, cmÀ1): 1608(w), 1547(m), 1485(s), 1446(m), 1333(m), 1069(s), 782(m),
710(s), 687(s). 1H NMR (CD2Cl2, d), 8.13–8.11 (m, 6H, ArH), 7.93 (d, 2H, NH,
2J(P,H) = 43 Hz), 7.55–7.49 (m, 9H, ArH) ppm. 13C NMR (CD2Cl2, d), 164.6 (d,
J(P,C) = 11.4 Hz, C@N), 131.7, 131.1, 129.2, 128.7, 128.4, 126.9, 125.3,
124.1 ppm. 31P NMR (CD2Cl2, d), À37.1 ppm. MS (EI+, m/z), 376 [M]+. HRMS
[CI+, m/z]: 377.1161 [M+H]+, calculated mass for C20H18O2N4P: 377.1162.
Compound 2: 0.153 g as a white solid in 58% yield. Mp 254–256 °C. Selected IR
(KBr, cmÀ1): 1613(m), 1594(m), 1491(s), 1397(m), 1333(vs), 1130(m),
1101(m), 1071(s), 1035(s), 1012(m), 896(m), 828(m), 733(m), 719(m),
694(s), 660(s), 480(m). 1H NMR (THF-d8, d), 8.22 (d, 2H, NH 2J(P,H) = 46 Hz),
7.67–7.63 (m, 4H, ArH), 7.53–7.49 (m, 5H, ArH), 7.35 (m, 4H, ArH) ppm. 13C
NMR (THF-d8, d), 154.0 (d, J(P,C) = 11.3 Hz, C@N), 138.1, 131.3, 130.0, 128.8,
128.5, 128.3, 128.2, 128.1, 127.9, 126.8, 123.3 ppm. 31P NMR (THF-d8, d),
À35.6 ppm. MS (EI+, m/z), 532 [M]+, 534 [M]+, 379 [M-PhBr]+. HRMS [EI+, m/z]:
531.99293 [M]+, calculated mass for C20H15O279Br2N4P: 531.9294.
Compound 3: 0.055 g as a yellow solid in 54% yield. Mp 242–244 °C. Selected IR
(KBr, cmÀ1): 1656(m), 1421(s), 1389(m), 1233(m), 1233(m), 1097(s), 829(m),
690(s). 1H NMR (CD2Cl2, d), 8.01–7.81 (m, 5H, ArH), 7.49 (d, 2H, NH
2J(P,H) = 44 Hz), 7.36–7.30 (m, 4H, ArH), 7.18–7.14 (m, 4H, ArH), 2.33 (s, 6H,
CH3) ppm. 13C NMR (CD2Cl2, d), 142.4 (d, J(P,C) = 11.4 Hz, C@N), 129.8, 129.4,
129.1, 128.5, 127.5, 126.7, 125.3, 121.4 ppm. 31P NMR (CD2Cl2, d), À37.4 ppm.
MS (EI+, m/z), 404 [M]+. HRMS [CI+, m/z]: 405.1478 [M+H]+, calculated mass for
X-ray crystal data for compounds 3, 5 and 6 were collected at 93 K by using a
Rigaku MM007 High brilliance RA generator/confocal optics and Mercury CCD
system. Intensity data were collected using
x steps accumulating area detector
images spanning at least a hemisphere of reciprocal space. All the data were
corrected for Lorentz polarization effects. Absorption effects were corrected on
the basis of multiple equivalent reflections or by semi-empirical methods.
Structures were solved by direct methods (SHELXTL25or Superflip26
) and
refined by full-matrix least-squares against F2 using the programme
SHELXTL.25 Hydrogen atoms bound to carbon were assigned riding isotropic
displacement parameters and constrained to idealized geometries, whereas
those bound to nitrogen were located from the difference Fourier map and
refined isotropically subject to a distance restraint. The thiophene in 6 was
found to be disordered, with occupancies of 0.7:0.3, the lower occupancy
component was refined anisotropically. Both components were subject to
distance restraints. CCDC-818632–818634 contains the supplementary
crystallographic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk.
Crystal data for compound 3: C22H21N4O2P, M = 404.40, monoclinic, space group
C
22H22O2N4P: 405.1475.
P21,
a = 11.457(4) Å,
b = 6.074(2) Å, c = 15.495(6) Å,
b = 107.218(9)°,
Compound 4: 0.175 g as a white solid in 76% yield. Mp 243–245 °C. Selected IR
(KBr, cmÀ1): 1613(m), 1594(m), 1490(m), 1397(s), 1333(vs), 1130(s), 1101(m),
1071(s), 1035(s), 1011(m), 894(m), 827(m), 732(m), 660(s), 479(m). 1H NMR
(DMSO-d6, d), 9.01 (d, 2H, NH 2J(P,H) = 47 Hz), 7.82–7.58 (m, 9H, ArH), 7.53–
7.37 (m, 4H, ArH) ppm. 13C NMR (DMSO-d6, d), 154.1 (d, J(P,C) = 11.4 Hz, C@N),
141.3, 138.1, 132.2, 131.4, 130.9, 129.5, 129.2, 128.9, 128.8, 128.6, 127.4, 125.9,
123.7 ppm. 31P NMR (DMSO-d6, d), À35.0 ppm. MS (EI+, m/z), 466 [M]+. HRMS
[CI+, m/z]: 467.0862 [M+H]+, calculated mass for C20H16O6N6P: 467.0869.
Compound 5: 0.080 g as a pale yellow solid in 27% yield. Mp 174–176 °C.
Selected IR (KBr, cmÀ1): 1536(m), 1449(s), 1406(s), 1236(m), 1078(m),
1048(m), 831(s), 691(vs). 1H NMR (CD2Cl2, d), 7.52 (d, J(H,H) = 6.3 Hz, 2H,
Thioph-H), 7.35 (d, J(H,H) = 6.3 Hz, 2H, Thioph-H), 7.13 (dd, J(H,H) = 6.3 Hz, 2H,
Thioph-H) ppm. 13C NMR (CD2Cl2, d), 164.1 (C@N), 129.7, 128.1, 127.6,
127.5 ppm. 77Se NMR (CD2Cl2, d), 689.6 ppm. MS (CI+, m/z), 298 [M+H]+.
U = 1029.9(7) A3, Z = 2,
l
= 0.16 mmÀ1
, 7292 reflections collected, 3544
independent reflections, Rint = 0.099, final R indices [I >2r(I)] R1 = 0.058, wR2
(all data) = 0.133. CCDC 818632.
Crystal data for compound 5: C10H6N2S2Se, M = 297.25, monoclinic, space group
P21/c, a = 6.227(3) Å, b = 9.516(4) Å, c = 18.225(7) Å, b = 95.951(11)°,
U = 1074.1(7) A3, Z = 4,
l , 6238 reflections collected, 2216
= 3.85 mmÀ1
independent reflections, Rint = 0.097, final R indices [I >2r(I)] R1 = 0.072, wR2
(all data) = 0.182. CCDC 818633.
Crystal data for compound 6: C16H13N4O2PS2, M = 388.39, monoclinic, space
group C2/c, a = 18.561(6) Å, b = 8.563(3) Å, c = 11.118(4) Å, b = 91.951(15)°,
U = 1766.1(10) A3, Z = 4,
l , 5000 reflections collected, 1755
= 0.41 mmÀ1
independent reflections, Rint = 0.058, final R indices [I >2r(I)] R1 = 0.091, wR2
(all data) = 0.207. CCDC 818634.