Reaction of 1,2,3-selenadiazoles with phosphines

Article abstract of DOI:10.1023/B:COHC.0000033546.79059.91

Nucleophilic attack of tributyl- and triphenylphosphines on 4-phenyl- and 5-ethoxycarbonyl-4-methyl-1,2,3-selenadiazoles leads to the quantitative formation of selenophosphoranes and substituted acetylenes. The molecular structure of 4-phenyl-1,2,3-selenadiazole was confirmed by X-ray crystallography.

Full text of DOI:10.1023/B:COHC.0000033546.79059.91

Chemistry of Heterocyclic Compounds, Vol. 40, No. 4, 2004
REACTION OF 1,2,3-SELENA-
DIAZOLES WITH PHOSPHINES
P. Arsenyan, K. Oberte, K. Rubina, S. Belyakov, and E. Lukevics
Nucleophilic attack of tributyl- and triphenylphosphines on 4-phenyl- and 5-ethoxycarbonyl-4-methyl-
1
,2,3-selenadiazoles leads to the quantitative formation of selenophosphoranes and substituted
acetylenes. The molecular structure of 4-phenyl-1,2,3-selenadiazole was confirmed by X-ray
crystallography.
Keywords: selenadiazole, selenium, phosphine, crystal structure, nucleophilic attack.
1
,2,3-Selenadiazole and its derivatives play an important role in the solution of many theoretical and
practical questions in organic chemistry [1] which explains the great interest of researchers in these compounds.
Compounds containing the selenadiazole ring show aromatic character, but they have a considerable tendency to
eliminate molecules of nitrogen and selenium with ring opening with formation of both acyclic compounds and
new heterocycles [2, 3], therefore they are promising materials for the investigation of the mechanism of some
reactions and for the synthesis of many compounds interesting in a practical sense [4].
A number of methods for the preparation of selenophosphoranes have been described in the literature.
Boiling of triphenylphosphine with metallic selenium in THF gave triphenylselenophosphorane in 66% yield [5],
while use of toluene increased the yield to 88% [6]. When selenium black was used in boiling toluene for 6 h the
yield increased to 100% [7]. Selenophosphorane was also formed by keeping triphenylphosphine and
tetrachloroselenotungsten (WCl Se) in toluene for 2 days [8]. Benzhydrylidenetriphenylphosphorane underwent
4
an exchange reaction with metallic selenium to give selenophosphorane in 71% yield [9, 10].
5
Triphenylselenophosphorane was formed on heating triphenyl(phenyl-p-tolylmethylene)-λ -phosphorane with
selenium in toluene at 85°C for 4 h [11].
In this work a method is developed for the preparation of selenophosphoranes from 4-phenyl- and
5
-ethoxycarbonyl-4-methyl-1,2,3-selenadiazoles.
-Phenyl-1,2,3-selenadiazole (1) reacted with tributylphosphine in benzene at room temperature. In the
4
first stage the Se–N bond is broken as a result of nucleophilic attack by tributylphosphine. Elimination of a
molecule of nitrogen follows. A molecule of phenylacetylene is released from the intermediate and
tributylselenophosporane (3) is produced. When triphenylphosphine is used, triphenylselenophosphorane (4) is
formed in quantitative yield only after boiling for one hour. In the case of 5-ethoxycarbonyl-4-methyl-1,2,3-
selenadiazole (2) selenophosphoranes 3 and 4 are formed in 100% yield. Ethyl but-2-ynecarboxylate (6) was
isolated from the reaction mixtures in 92% yield.
_
_________________________________________________________________________________________
Latvian Institute of Organic Synthesis, Riga, LV -1006; e-mail: pavel.arsenyan@lycos.com. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 599-603, April 2004. Original article submitted
October 7, 2003.
0
009-3122/04/4004-0503©2004 Plenum Publishing Corporation
503

R
N
R
-
R''3P
N
+
PR''3
R''3P
Se
R
R'
+
–
N2
Se
, 2
3, 4
5, 6
R'
Se
R'
1
1
, 5 R = Ph, R' = H; 2, 6 R = Me, R' = COOEt; 3 R" = Bu; 4 R" = Ph
When trimethyl- or triethyl phosphite was used the reaction stopped at the first stage to give
selenophosphates [12]. Destruction of the selenadiazole ring with phosphines is an alternative method for the
preparation of substituted acetylenes under mild conditions.
The molecular structure of compound 1 was determined by X-ray diffractometry (Fig. 1).
In the crystalline state the molecule of selenadiazole 1 is practically planar with a torsion angle C(5)–
C(4)–C(6)–C(7) of 178.6°. The C(5)–Se(1) bond (1.814 A) is shorter than the N(2)–Se(1) bond (1.878 A), and
the C(5)–Se(1)–N(2) angle equals to 86.41° (Tables 1 and 2). There are 8 independent molecules in the unit cell.
TABLE 1. Bond Lengths and Intermolecular Contacts (l) in Compound 1
Bond
Se(1)–C(5)
l, Å
Bond
l, Å
1.814(3)
1.405(4)
1.472(5)
1.371(4)
1.387(4)
1.391(5)
1.07(3)
Se(1)–N(2)
C(6)–C(11)
C(5)–C(4)
C(11)–C(10)
N(3)–N(2)
C(9)–C(10)
C(7)–H(7)
C(8)–H(8)
C(10)–H(10)
1.878(3)
1.391(4)
1.355(4)
1.389(4)
1.265(4)
1.367(5)
0.990(3)
1.04(4)
C(6)–C(7)
C(6)–C(4)
C(7)–C(8)
N(3)–C(4)
C(8)–C(9)
C(5)–H(5)
C(11)–H(11)
C(9)–H(9)
0.96(3)
1.03(4)
1.10(3)
Contact
l contact, Å
Contact
l contact, Å
Se(1)···Se(1)
Se(1)···Se(1)
3.8062(8)
3.6294(8)
Se(1)···N(2)
N(2)···H(5)
3.379(3)
2.59(3)
Fig. 1. Molecular structure of 4-phenyl-1,2,3-selenadiazole (1).
5
04

a
b
Fig. 2. Crystal Packing of Compound 1: Projections Along the Y (a) and Z (b) Axes.
TABLE 2. Torsion Angles (τ) in Compound 1
Angle
τ, deg.
Angle
τ, deg.
C(5)–Se(1)–N(2)
C(7)–C(6)–C(4)
Se(1)–C(5)–C(4)
C(6)–C(11)–C(10)
C(7)–C(8)–C(9)
C(11)–C(10)–C(9)
C(6)–C(4)–N(3)
Se(1)–N(2)–N(3)
C(4)–C(5)–H(5)
C(8)–C(7)–H(7)
C(10)–C(11)–H(11)
C(9)–C(8)–H(8)
C(10)–C(9)–H(9)
C(9)–C(10)–H(10)
86.41(12)
120.6(2)
111.0(2)
120.8(3)
120.9(3)
120.2(3)
119.3(2)
110.9(2)
126.(2)
C(7)–C(6)–C(11)
C(11)–C(6)–C(4)
C(6)–C(7)–C(8)
C(4)–N(3)–N(2)
C(8)–C(9)–C(10)
C(6)–C(4)–C(5)
C(5)–C(4)–N(3)
Se(1)–C(5)–H(5)
C(6)–C(7)–H(7)
C(6)–C(11)–H(11)
C(7)–C(8)–H(8)
C(8)–C(9)–H(9)
C(11)–C(10)–H(10)
118.4(3)
121.0(3)
120.1(3)
117.3(3)
119.7(3)
126.4(3)
114.3(3)
122.(2)
115.(2)
125.(2)
119.(2)
121.(2)
121.(2)
118.(2)
115.(2)
125.(2)
123.7(13)
116.0(14)
There are intermolecular contacts between selenium atoms of neighbouring molecules of selenadiazole 1 crystal
within the limits of 3.63-3.81 Å, which is less than the sum of the van der Waals radii [13]. In addition to
Se(1)···Se(1) contacts there are Se(1)···N(2) and N(2)···H(5) contacts of 3.38 Å and 2.59(3) Å respectively.
EXPERIMENTAL
For the X-ray Structural Analysis 1961 reflections were measured with a Nonius KappaCCD
diffractomer using molybdenum radiation, MoKα (0.7103 Å). Monocrystals of compound 1 (mp 76-77°C)
grown from acetone–water (60:40) were monoclinic with unit cell parameters: a = 36.833(2), b = 5.7406(2),
3
3
-1
c = 7.3839(4) Å; β = 92.975(2)°; V = 1559.44(13) Å ; D = 1.781 g/cm ; µ = 4.74 cm ; coefficient of absorption
x
5
05

-
1
4
F
.74 mm ; space group P21/a; Z = 8. In the calculations 1114 independent reflections with |F| > 2σ were used
for 124 refined parameters. The final residual factor was 0.057. Calculations were carried out using a suite of
programs [14-16].
Selenophosphoranes 3, 4 (General Method). Mixture of equimolar amounts of 1,2,3-selenadiazole and
phosphine was dissolved in benzene and stirred for 1 h (it was necessary to boil the mixture for
triphenylphosphine). The reaction mixture was evaporated and selenophosphoranes separated in quantitative
yield from the substituted acetylenes by crystallization from hexane. The structure of the products was confirmed
by mass and NMR spectra [6, 8].
The authors express their sincere thanks to the Latvian Committee on Science (grant no. 189) for
financial support.
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