Novel reactivity of tetracoordinate 1,2λ4-oxaselenetanes: Oxirane formation reaction with retention of configuration

Article abstract of DOI:10.1039/a704277i

Stable tetracoordinate 3-phenyl-1,2λ⁴-oxaselenetanes give the corresponding oxiranes upon thermolysis; in sharp contrast to Corey-Chaykovsky type reactions, oxirane formation proceeds with retention of configuration, and the reaction can be recognised as a new type of carbon-oxygen ligand coupling reaction of λ⁴-selenanes.

Full text of DOI:10.1039/a704277i

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4
Novel reactivity of tetracoordinate 1,2l -oxaselenetanes: oxirane formation
reaction with retention of configuration
Fumihiko Ohno, Takayuki Kawashima*† and Renji Okazaki*
Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
ButMe2SiO
CF3
CF3
4
F3C
CF3
OLi
F3C
CF3
OH
Stable tetracoordinate 3-phenyl-1,2l -oxaselenetanes give
the corresponding oxiranes upon thermolysis; in sharp
contrast to Corey–Chaykovsky type reactions, oxirane
formation proceeds with retention of configuration, and the
reaction can be recognised as a new type of carbon–oxygen
i –iii
iv
Li
SeBn
6 (79%)
SeBn
7 (88%)
5
4
v–vii
ligand coupling reaction of l -selenanes.
ButMe2SiO
CF3
CF3
F3C
CF3
F3C
CF3
OH
The reactions of carbonyl compounds with phosphorus ylides
viii, iii
(Wittig reaction) afford alkenes via 1,2l -oxaphosphetanes,1
5
ix
O
while those with group 16 element (S, Se, Te) ylides (Corey–
Chaykovsky type reaction) give oxiranes.2 The latter type of
oxirane formation reaction has been proposed to involve the
formation of an anti-betaine followed by a back side attack of an
oxido anion on the b-carbon.2,3 In the course of our study on
oxetanes bearing a highly coordinate main group element at the
position adjacent to the oxygen atom,4 we have reported the
syntheses and isolations of tetra- and penta-coordinate 1,2-oxa-
thietanes 1 and 2, and the oxirane formation reaction with
Ph
Ph
Ph
Se
Se
O
Se
R1
R2
R1
R2
R1
R2
HO
HO
8a (93%)
b (13%)
c (50%)
d (42%)
4a (54%)
b (44%)
c (56%)
d (65%)
9a (96%)
b (72%)
c (89%)
d (86%)
a R1 = R2 = Ph
b R1 = R2 = CF3
c R1 = Ph, R2 = CF3
d R1 = CF3, R2 = Ph
F3C
CF3
F3C
CF3
O
O
H
Ph
Scheme 1 Reagents and conditions: i, Se, THF, 0 °C, then 25 °C, 12 h; ii,
BnBr, 0 °C, then 25 °C, 2 h; iii, aq. NH4Cl; iv, ButMe2SiOSO2CF3, Et3N,
CH2Cl2, 0 °C, then 40 °C, 1 d; v, LDA (2 equiv.), THF, 278 °C, 20 min;
vi, R1R2CNO, THF, 278 °C, 30 min; vii, flash column chromatography (for
8c and 8d); viii, Bun4NF (2 equiv.), THF, 0 °C, 30 min; ix, Et3N (2 equiv.),
Br2 (1 equiv.), CCl4, 0 °C, then 25 °C, 4 h.
Se
O
S
R
R1
R2
R1
R2
O
1 R = lone pair
2 R = O
3
R
R
+
X
–
O
proton of the 3-carbon and the ortho-protons of the phenyl
group of the 4-carbon was observed for 4c but not for 4d.
The results of thermolysis (C6D5CD3, in a degassed sealed
tube) of 4 are summarised in Scheme 2 and Table 1. Although
the yield of oxirane 10a from the 3,4,4-triphenyl derivative 4a
was low because of concomitant phenyl-migrated ketone
formation, 4b gave oxirane 10b almost quantitatively. Further-
more, thermolysis of 4c and 4d afforded the corresponding
oxirane stereospecifically in high yield with retention of the
relative stereochemistry of the starting oxaselenetanes, although
a small amount (2%) of an inverted product was obtained from
4c.
anti-betaine
retention of configuration in the thermolysis of 2.5 This
stereochemistry suggests another possible mechanism for the
Corey–Chaykovsky reaction, i.e. the formation and carbon–
oxygen ligand coupling reaction6 of intermediary highly
coordinate 1,2-oxathietanes, which prompted us to examine the
reactivity of such a species on changing the central atom from
sulfur to a heavier chalcogen. Although no oxirane formation
was observed in the thermolysis of the first tetracoordinate
1,2l -oxaselenetanes 3 having no substituent at the 3-position,7
4
These results indicate that the stereochemistry of the oxirane
formation from 1,2-oxaselenetanes 4 is the reverse of that
3-phenyl derivatives were expected to give the corresponding
oxiranes in view of the reactivity of the sulfur analogues. We
now report on the first example of oxirane formation from
O
F3C CF3
R1
R2
H
R2
H
O
O
4
tetracoordinate 1,2l -oxaselenetanes and the stereochemistry of
Ph
+
+
+
R
the reaction.
O
Se
Ph R1
Ph
Tetracoordinate 3-phenyl-1,2-oxaselenetanes 4‡ were syn-
thesised from 58 by the same method as that for the synthesis of
sulfur analogues 1 (Scheme 1).5§ The 19F and 1H NMR spectra
of the crude reaction mixtures showed the signals due to the
diastereoisomers of 4 in which the phenyl group was cis to the
lone pair. However, the cis isomers were less stable toward
hydrolysis than 4 and gradually decomposed in the course of
purification. All compounds 4 were stable colourless plates at
room temperature in the air. The relative stereochemistry
between the 3- and 4-positions of 4c and 4d was determined by
differential NOE experiments; an NOE between the methine
Ph
10
10′
13
11 R = Ph
12 R = CF3
heat
4
F3C CF3
O
C6D5CD3
Ph
sealed
tube
+
O
R
Se
Ph
14 R = Ph
16
15 R = CF3
Scheme 2
Chem. Commun., 1997
1671

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4
Table 1 Yields of products in the thermolysis of 1,2l -oxaselenetanes 4
Yield (%)a
R1
R2
T/°C
t
10
10A
11
12
13
14
15
16
b
c
4a
4b
4c
4d
Ph
CF3
Ph
Ph
130
200
200
200
3 d
6 d
30 h
5 h
43
quant.
88
—
—
2
52
—
—
—
—
—
8
95
quant.
97
—
—
—
—
—
—
2
5
—
2
b
CF3
CF3
Ph
CF3
quant.
—
—
quant.
—
—
a Estimated by 19F and 1H NMR spectroscopy. b 10A is equal to 10. c Observed by GC–MS.
7.32–7.41 (m, 3 H), 7.44–7.51 (m, 3 H), 7.54 (d, 3J 7.6, 4 H), 7.64–7.68 (m,
2 H), 7.75–7.81 (m, 1 H), 8.57 (d, 3J 7.9, 1 H); 77Se NMR (CDCl3, 95 MHz):
d 792.9 (q, 4JSeF 27). Calc. for C24H15F9O2Se: C, 49.25; H, 2.58. Found: C,
49.25; H, 2.64%.
For 4d: colourless plates (hexane–Et2O); mp 149.0–150.5 °C (decomp.);
1H NMR (CDCl3, 500 MHz): d 6.46 (s, 1 H, SeCHPh), 6.85 (d, 3J 7.4, 2 H),
7.16–7.32 (m, 8 H), 7.74–7.79 (m, 2 H), 7.85–7.90 (m, 1 H), 8.57 (d, 3J 8.0,
1 H); 77Se NMR (CDCl3, 51.5 MHz): d 781.0 (s). Calc. for C24H15F9O2Se:
C, 49.25; H, 2.58. Found: C, 49.39; H, 2.70%. Satisfactory 13C and 19F
NMR spectra were obtained for both 4c and 4d.
§ In the synthesis of 8b, other products formed by an electrophilic reaction
of hexafluoroacetone at the para-position of the benzyl group were
obtained.
¶ The phenyl migration in 4c and 4d was additionally retarded by the
electronic effect of the adjacent trifluoromethyl group.
F3C
CF3
F3C
CF3
O
O
δ+
Se
H
H
heat
Ph
Ph
Se
O
R1
R2
R1
R2
O
δ–
4
F3C
CF3
R1
R2
O
H
+
O
Ph
Se
10
13
retention
∑ Although the stereochemistry of the oxirane formation from 4,4-diaryl-
3-phenyl derivatives has not been elucidated, it is unlikely that the
trifluoromethyl group at the 4-position changed its stereochemistry
completely, because the electron-withdrawing group of the position can
electronically stabilise both the ground state and the transition state.
Scheme 3
expected from the back side attack of the oxido anion, and hence
the reaction can be recognised as a carbon–oxygen ligand
coupling reaction of l -selenanes (Scheme 3). In the thermol-
4
1 For reviews, see I. Gosney and A. G. Rowley, in Organophosphorus
Reagents in Organic Synthesis, ed. J. I. G. Cadogan, Academic Press,
New York, 1979, pp. 17–153; B. E. Maryanoff and A. B. Reitz, Chem.
Rev., 1989, 89, 863.
ysis of 4, migration of the phenyl group on the 4-carbon¶ and
deprotonation from the 3-position by the oxido anion can be
considered to be sterically inhibited by the phenyl group on the
3-position, which is absent in 3. Moreover, it can be assumed
that the phenyl group on the 3-carbon assists the Se–C bond
cleavage by stabilising the anionic character of the 3-carbon
induced in the transition state.
2 For the Corey–Chaykovsky reaction, see J. Aube´, in Comprehensive
Organic Synthesis: Selectivity, Strategy, and Efficiency in Modern
Synthetic Chemistry, ed. B. M. Trost and I. Fleming, Pergamon, Oxford,
1991, vol. 1, pp. 822–825. For aminosulfoxonium ylides, see C. R. John-
son, Acc. Chem. Res., 1973, 6, 341. For selenonium ylides, see A. Krief,
W. Dumont, D. Van Ende, S. Halazy, D. Labar, J.-L. Laboureur and
T. Q. Leˆ, Heterocycles, 1989, 28, 1203. For telluronium ylides, see
A. Osuka and H. Suzuki, Tetrahedron Lett., 1983, 24, 5109; L.-L. Shi,
Z.-L. Zhou and Y.-Z. Huang, Tetrahedron Lett., 1990, 29, 4173;
Z.-L. Zhou, Y.-Z. Huang, L.-L. Shi and J. Hu, J. Org. Chem., 1992, 57,
6598.
3 C. R. Johnson and C. W. Schroeck, J. Am. Chem. Soc., 1971, 93, 5303;
T. Durst, R. Viau, R. Van Den Elzen and C. H. Nguyen, J. Chem. Soc.,
Chem. Commun., 1971, 1334; J. M. Townsend and K. B. Sharpless,
Tetrahedron Lett., 1972, 3313; T. Durst, C. R. Johnson, C. W. Schroeck
and J. R. Shanklin, J. Am. Chem. Soc., 1973, 95, 5298.
In the case of the sulfur analogues 1,5a,b oxirane formation
was observed to a minor extent, with fragmentation back to the
starting ketone or isomerisation via a 1,3-proton shift being the
major decomposition pathways; this made it difficult to
elucidate the reaction mechanism although oxirane formation
from 1 with retention of configuration was observed.9 In sharp
contrast, in the reaction of 4c and 4d, yields of oxirane were
almost quantitative and the stereochemistry exhibited 96 and
100% retention of configuration, respectively. The present
results and the stereochemistry of the thermolysis of 25c
strongly suggest that such a concerted oxirane formation from
highly coordinate oxachalcogenetanes generally proceeds re-
gardless of the central atom or its coordination number.∑
This work was partially supported by a Grant-in-Aid for
Scientific Research on Priority Area (No. 09239101) (T. K.)
from the Ministry of Education, Science, Sports and Culture,
Japan. F. O. is grateful for a Research Fellowship from the
Japan Society for the Promotion of Science for Young
Scientists. We thank Shin-etsu Chemicals, Central Glass and
Tosoh Akzo Co. Ltd. for gifts of silyl chlorides, organofluorine
compounds, and alkyllithiums, respectively.
4 T. Kawashima and R. Okazaki, Synlett, 1996, 600 and references cited
therein.
5 (a) T. Kawashima, F. Ohno and R. Okazaki, Angew. Chem., Int. Ed.
Engl., 1994, 33, 2094; (b) F. Ohno, T. Kawashima and R. Okazaki, J. Am.
Chem. Soc., 1996, 118, 697; (c) T. Kawashima, F. Ohno, R. Okazaki,
H. Ikeda and S. Inagaki, J. Am. Chem. Soc., 1996, 118, 12455.
6 For a recent review, see S. Oae and Y. Uchida, Acc. Chem. Res., 1991, 24,
202. For a recent example, see S. Ogawa, S. Sato and N. Furukawa,
Tetrahedron Lett., 1992, 33, 7925.
7 T. Kawashima, F. Ohno and R. Okazaki, J. Am. Chem. Soc., 1993, 115,
10434.
8 E. F. Perozzi, R. S. Michalak, G. D. Figuly, W. H. Stevenson III,
D. B. Dess, M. R. Ross and J. C. Martin, J. Org. Chem., 1981, 46,
1049.
Footnotes and References
9 F. Ohno, T. Kawashima and R. Okazaki, unpublished results.
† E-mail: takayuki@chem.s.u-tokyo.ac.jp
‡ Selected data for 4c: colourless plates (hexane–Et2O); mp 192.4–194.0 °C
(decomp.); 1H NMR (CDCl3, 500 MHz): d 6.21 (s, 1 H, SeCHPh),
Received in Cambridge, UK, 18th June 1997; 7/04277I
1672
Chem. Commun., 1997