Selenocarbonyl synthesis using Woollins reagent

Article abstract of DOI:10.1016/S0040-4039(01)01113-3

[PhP(Se)(μ-Se)]₂ selenates secondary and tertiary amides to the corresponding selenoamides in 30-70% yields at 130°C in toluene and indolizine-3-aldehydes to selenoaldehydes in 40-59% yield at 25°C.

Full text of DOI:10.1016/S0040-4039(01)01113-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5949–5951
Selenocarbonyl synthesis using Woollins reagent
Pravat Bhattacharyya and J. Derek Woollins*
School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
Received 6 June 2001; accepted 21 June 2001
Abstract—[PhP(Se)(m-Se)] selenates secondary and tertiary amides to the corresponding selenoamides in 30–70% yields at 130°C
2
in toluene and indolizine-3-aldehydes to selenoaldehydes in 40–59% yield at 25°C. © 2001 Elsevier Science Ltd. All rights
reserved.
The utility of selenocarbonyl compounds as intermedi-
ates in heterocycle synthesis and increasing interest in
the bioactivity of organoselenium compounds necessi-
tates the development of new techniques for the intro-
duction of selenium into organic molecules. One
popular modus operandi is selenation, the exchange of
a carbonyl oxygen atom for selenium. In 1997 Hill and
co-workers reported the use of ‘Woollins reagent’,
obtained from (PhP)5 and elemental selenium (P:Se
ratio 1:2), for converting tungsten(V) and molybde-
num(V) ketenyl complexes to their selenoketenyl coun-
with the thionation agent [(p-MeOC H )P(S)(m-S)]
6
4
2
(Lawesson’s reagent). Although 1 has not received fur-
ther attention as a selenation reagent, we have recently
found this compound to be active towards a range of
unsaturated organic substrates to give several unusual
2
–4
phosphorus containing heterocycles.
We communi-
cate here our usage of 1 for the selenation of amides
and aldehydes.
Compound 1, available in 60–70% yield upon oxidation
5
–7
of (PhP) with 10 equiv. of selenium (Fig. 1),
was
5
1
terparts, speculating upon the identity of Woollins
reagent as 2,4-bis(phenyl)-1,3-diselenadiphosphetane-
heated together with 3 equiv. of amide in toluene at
130°C for the duration indicated (Table 1). Conversion
is accompanied by the disappearance of insoluble 1 and
2
,4-diselenide [PhP(Se)(m-Se)] 1. Our subsequent crys-
2
2
tallographic analysis confirmed 1 to be isostructural
a
Table 1. Selenation using 1
Product
Reaction time (h)
Isolated yield (%)
I
II
1
2
7
1
21
2
2
2
2
2
72
70
30
13
38
44
47
53
59
40
III
IV
V
VI
VII
VIII
IX
X
a
Reactions were conducted under dinitrogen, subsequent operations
were performed in air. For I–VII, a mixture of 1 (0.2 mmol) and the
3
substrate (0.6 mmol) in anhydrous toluene (2 cm ) was heated at
1
30°C. The resulting orange solution was cooled to room tempera-
ture, the solvent was removed in vacuo and the selenoamide purified
by column chromatography on silica (dichloromethane). Physical
Figure 1. Structures of 1–4.
1
4–17
data for I–VII were in accord with literature values.
For the
Keywords: selenoamide; selenoaldehyde; selenation; Woollins reagent.
indolizine-3-aldehydes the reactions were performed at 25°C on a
similar scale to the amides, the products VIII–X being purified by
column chromatography on alumina (9:1 v/v toluene/diethyl ether).8
*
Corresponding author. Tel.: +44-1334-463861; fax: +44-1334-
63384; e-mail: jdw3@st-and.ac.uk
4
0
040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01113-3

5
950
P. Bhattacharyya, J. D. Woollins / Tetrahedron Letters 42 (2001) 5949–5951
Figure 2. Selenocarbonyl products formed using 1.
precipitation of minor quantities of selenium; while 1 is
appreciably more soluble in pyridine than toluene at
elevated temperatures, no enhancements in yield are
noted when this solvent is used. Chromatographic
purification of I–VII (Fig. 2) on silica removed all
phosphorus(V) by-products, characterisation being per-
rocycles available from the (PhP) /Se system, namely
5
(PhP) Se 2, (PhP) Se 3 and (PhP) Se 4 (Fig. 1), pre-
4
3
2
3
3
pared by treating (PhP) with 1.25, 3.33 or 5 equiv. of
5
5,6
selenium in refluxing toluene. Using PhC(O)NMe as
2
substrate and under identical conditions to 1 we found
that 2 and 3 gave 5 and 19% yields, respectively, of
1
13
1
formed using H and C{ H} NMR, IR and mass
PhC(Se)NMe after 20 h at 130°C, while 4 gave 42%
2
spectroscopies. The 72% yield of PhC(Se)NMe from
yield after 1 h, underlining the importance of a PꢀSe
bond for high activity. For 2–4 chromatography
afforded, in addition to selenoamide, a phosphorus(V)
by-product (lP 24.5) which is tentatively assigned to
2
PhC(O)NMe compares favourably with the selenation
2
of 3-CH C H C(O)NEt by PhP(Se)Cl (61% yield after
3
6
4
2
2
8
5
h at 95–100°C) and the 50% yield after 220 h at 90°C
using (RP) Se [R=2,4- Bu (6-OMe)C H ].
t 9,10
Notably
PhP(O)(OH) , while for 2 unreacted heterocycle can be
3
5
2
6
2
2
only a 38% yield of PhC(Se)NMe using 1 is obtained
recovered. Although 2–4 exhibit some selenation capa-
bility their air sensitivity and highly unpleasant odours
compared with 1 precludes their wider usage.
2
after 1 h when selenation is carried out in pyridine.
Secondary amides are readily converted to
selenoamides by 1; in our hands neither PhC(O)NHMe
nor o-caprolactam were selenated satisfactorily using
The stability (shelf life of several months in air, indefin-
itely under nitrogen), ease of preparation and handling
of 1 contrasts markedly with reagents such as NaHSe,
PhP(Se)Cl , transformations which 1 effects in 70 and
2
4
4% yields, respectively. The slow conversion for
t
t
i
PhC(O)NH Bu reflects retardation due to the bulky Bu
substituent. Tetramethyloxamide is converted to the
selenoxamide Me NC(Se)C(O)NMe in 38% yield after
H Se, ( Bu Al) Se, (Me Si) Se and bis(1,5-cyclooc-
2
2
2
3
1–14
2
1
tanediylboryl)selenide,
which are either air/mois-
ture sensitive or require fresh preparation prior to use.
Additionally, substrates containing NH groups can be
satisfactorily selenated by 1, which does not appear to
2
2
2
1 h, with minor quantities (typically 2–3%) of the
diselenoxamide formed. While N,N%-diethylurea is con-
verted to (EtNH) CSe in moderate yield, N,N%-diphenyl-
be the situation for PhP(Se)Cl . Facile purification of
2
2
urea does not give (PhNH) CSe but an (as yet) unchar-
the selenocarbonyls allied to its moderate tolerance
towards amine protons makes 1 stand out as a selena-
tion reagent of great promise. We are currently investi-
gating the latitude of the reactivity of Woollins reagent
towards a range of carbonyl containing substrates.
2
1
acterised phosphorus compound (l 47.0, J 853 Hz).
P
PSe
1
also converts indolizine-3-aldehydes to the selenoalde-
hydes VIII–X at 25°C in yields of 40–59% after 2 h, cf.
2–81% after 10 min at room temperature using
6
8
PhP(Se)Cl . Benzamide is reluctant to undergo selena-
2
tion using 1, yields of PhC(Se)NH struggle to reach
2
double figures; we are unable to convert nicotinamide
Acknowledgements
to pyC(Se)NH under any conditions.
2
3
1
1
P{ H} NMR of a crude mixture from the selenation
We are grateful to the EPSRC (P.B.) for funding.
of PhC(O)NMe contain several sets of doublets cen-
2
tred at 75 and 2 ppm, indicating PꢀSe and PꢀO envi-
3
1
31
ronments, respectively. The P– P couplings, typically
3
6–50 Hz, suggest PꢁEꢁP (E=O or Se) linkages, per-
References
haps within a cyclic structure resembling the trimer
t
[
RP(O)(m-O)] [R=2,4- Bu (6-OMe)C H ] isolated by
1. Baxter, I.; Hill, A. F.; Malget, J. M.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Chem. Commun. 1997,
2049.
3
2
6
2
9,10
Yoshifuji in selenation reactions using (RP) Se .
We
3
5
also investigated the selenating capacity of other hete-

P. Bhattacharyya, J. D. Woollins / Tetrahedron Letters 42 (2001) 5949–5951
5951
2
3
4
5
. Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D. J.
Chem. Soc., Dalton Trans. 2001, 300.
. Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D.
Angew. Chem., Int. Ed. 2000, 39, 1973.
. Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D. J.
Organomet. Chem. 2001, 623, 116.
. Pilkington, M. J.; Slawin, A. M. Z.; Williams, D. J.;
Wood, P. T.; Woollins, J. D. Heteroatom Chem. 1990, 1,
11. Li, G. M.; Zingaro, R. A. J. Chem. Soc., Perkin Trans.
1998, 647.
12. Li, G. M.; Zingaro, R. A.; Segi, M.; Riebenspies, J. H.;
Nakajima, T. Organometallics 1997, 16, 756.
13. Shimada, K.; Jin, N.; Kawaguchi, M.; Dobashi, K.;
Nagano, Y.; Fujimura, M.; Kudoh, E.; Kai, T.; Saito, N.;
Masuda, J.; Iwaya, M.; Fujisawa, H.; Aoyagi, S.;
Takikawa, Y. Bull. Chem. Soc. Jpn. 1997, 70, 197.
14. Takikawa, Y.; Watanabe, H.; Sasaki, R.; Shimada, K.
Bull. Chem. Soc. Jpn. 1994, 67, 876.
3
51.
6
7
8
9
. Fitzmaurice, J. C.; Williams, D. J.; Wood, P. T.;
Woollins, J. D. J. Chem. Soc., Chem. Commun. 1988, 741.
. Wood, P. T.; Woollins, J. D. J. Chem. Soc., Chem.
Commun. 1988, 1190.
15. Jensen, K. A.; Nielsen, P. H. Acta Chem. Scand. 1966, 20,
597.
16. Rae, I. D.; Wade, M. J. Int. J. Sulfur Chem. 1976, 8, 519.
17. Selected data for Me NC(O)C(Se)NMe : l (CDCl3,
. Michael, J. P.; Reid, D. H.; Rose, B. G.; Speirs, R. A. J.
2
2
H
Chem. Soc., Chem. Commun. 1988, 1494.
300.0 MHz): 3.45 (s, 3H), 3.15 (s, 3H), 3.00 (s, 3H),
2.95 (s, 3H). lC (75.3 MHz): 197.9 (CꢀSe), 168.0 (CꢀO),
44.0, 43.7, 37.9, 34.6 (CH3). Found (calcd for
C H N OSe): C 35.8 (34.8), H 6.0 (5.8), N 13.4 (13.5)%.
. An, D. L.; Toyota, K.; Yasunami, M.; Yoshifuji, M.
Chem. Lett. 1995, 199.
1
0. Yoshifuji, M.; Higeta, N.; An, D. L.; Toyota, K. Chem.
6
12
2
+
Lett. 1998, 17.
EI: m/z 207, M .
.