Diastereoselective oxyselenylation of 1,n-diolefins utilizing PET generated [PhSeSePh]+ · as an electrophilic species: An efficient and general strategy for the synthesis of α,α'-trans-dialkyl cyclic ethers

Article abstract of DOI:10.1055/s-1999-2809

PET generated electrophilic species [PhSeSePh]⁺ · is found to effect stereoselective oxyselenylation of 1,n-diolefins (1) leading to a novel strategy for the synthesis of α,α'-trans-dialkyl cyclic ethers (5) in good yields.

Full text of DOI:10.1055/s-1999-2809

LETTER
1257
Diastereoselective Oxyselenylation of 1,n-Diolefins Utilizing PET Generated
[PhSeSePh]+. as an Electrophilic Species: An Efficient and General Strategy
for the Synthesis of α,α′-trans-Dialkyl Cyclic Ethers
Ganesh Pandey*, R. Sochanchingwung, Shashi Kant Tiwari
Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune - 411008, INDIA.
Fax 91-(020)-393153; Email : pandey@ems.ncl.res.in
Received 26 May 1999
Abstract: PET generated electrophilic species [PhSeSePh]+. is
found to effect stereoselective oxyselenylation of 1,n-diolefins (1)
leading to a novel strategy for the synthesis of α,α′-trans-dialkyl
cyclic ethers (5) in good yields.
Key Words: photosensitized electron transfer (PET), episelenoni-
um radical cation, oxyselenylation, α,α′-dialkyl cyclic ethers.
Figure 1
Stereoselective synthesis of α,α′-dialkyl cyclic ethers
[PhSeSePh]+. employing 1,4- dicyanonaphthalene (DCN)
have attracted considerable attention, recently, owing to
as light-harvesting electron acceptor
their unique structural features and presence in the large
through the photosystem as shown in fig.1 and the utility
of this transient species was suggested for the efficient
selenoetherification9 and enyne cyclisation10 reactions.
Intrigued by the possible utilisation of [PhSeSePh]+. for
trans-selective oxyselenylation of 1, owing to the envis-
aged syn-addition11 of the hydroxyl group to the episele-
nonium radical cation12 moiety from the expected
transition state structure 4, we initiated our study and are
pleased to disclose herein the success and application of
our concept for the synthesis of various α,α′-trans-dialkyl
substituted tetrahydrofurans, tetrahydropyrans and ox-
epanes.
number of polyether antibiotics and other biologically ac-
tive natural products1. In majority of these natural prod-
ucts, cyclic ether units display α,α′-trans-dialkyl
substituents. For example, majority of Annonaceous ace-
togenins possess trans-2,5-dialkyl tetrahydrofurans2
while swinholides,3 potent cytotoxic agents4, and
laurapinnacins5 display trans-2,6-dialkyl tetrahydropyran
and trans-2,7-dialkyl oxepans moieties, respectively.
Among the various strategies reported6 for the synthesis
of these structural units, bis addition of an oxygen nucleo-
phile across the 1,n-diolefins (dienes) moiety represents
an attractive approach,7 however, these strategies afforded
mixture of diastereomers. Oxyselenylation of diolefins 1,
reported8 by using PhSeCN-CuCl2 or PhSeCl as reagents
in aqueous acetonitrile, though, is known to produce α,α′-
dialkyl cyclic ethers, however, this strategy apart from
utilising very toxic and unstable reagents is also not stere-
oselective. The non-stereoselectivity of these reagents
may be understood by considering the possible lack of
steric restriction for the face selection from the transition
Scheme 2
The [PhSeSePh]+. mediated oxyselenylation reaction was
initially carried out by irradiating a mixture of 1,5-hexadi-
ene (1, n=1) (6.0 mmol), PhSeSePh (6.0 mmol), and DCN
(0.6 mmol) in CH3CN:H2O (4:1) solvent, utilizing 450-W
Hanovia medium pressure lamp without removing dis-
solved oxygen from the solvent. The lamp was housed in
a water cooled pyrex immersion vessel which allowed
only >280 nm light to pass through. Under the irradiation
condition mentioned, most of the light was absorbed by
DCN only. After about 8 h of irradiation when 1 was sub-
stantially consumed (60%, monitored by GC) photolysis
was discontinued. Removal of the solvent followed by
column chromatographic purification of the crude pho-
tolysate gave 5 (n=1) in 80% yield. The yield of 5 was cal-
culated based on the starting material utilized.
Scheme 1
state structure 2 during the intramolecular selenoetherifi-
cation step.
Few years back, we had reported9, 10 a photosensitized
electron transfer (PET) strategy of activating PhSeSePh
for in situ generation of electrophilic selenium species
Synlett 1999, No. 8, 1257–1258 ISSN 0936-5214 © Thieme Stuttgart · New York

1258
G. Pandey et al.
LETTER
Diastereomeric purity of 5 in >97% was established by
comparing the HPLC analysis (reverse phase, C18 Bonda
pack 0.5 µm column) with the authentic mixture prepared
by following the reported8 procedure. The characteriza-
tion and confirmation of the 2,5-trans-stereochemistry for
Acknowledgement
One of us (RS) is thankful to CSIR, New Delhi for financial support.
References and Notes
1
5 was established by detailed H NMR, 13C NMR and
(1) Westley, J. W. Ed., Polyether Antibiotics; Naturally
Occurring Acid Ionophores. Marcell-Dekkar,New York,
1983, Vol. I & II.
mass spectral analysis. DCN was recovered almost quan-
titatively (≈ 98 %) at the end of the reaction.
(2) (a) Rupprecht, J.K.; Hui, Y.- H.; Mc Laughlin, J. L., J. Natural
Products, 1990, 53, 237. (b) Hoppe, R.; Scharf, H.-D.
Synthesis 1995, 1447. (c) Koert, U., Synthesis, 1995, 115.
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(4) Doi, M.; Ishida, T.; Kobayashi, M.; Kitagawa, I., J. Org.
Chem. 1991, 56, 3629.
Table: trans-selective Oxyselenylation of 1,n-diolefins
(5) Kotsuki, H.; Ushio, Y.; Kadota, I.; Ochi, M., J. Org. Chem.
1989, 54, 5153. and references cited therein.
(6) (a) Elliott, M.C. J. Chem. Soc. Perkin Trans.1 1998,4175.
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Chem. Commun. 1989, 416.( b) Pandey, G.; Soma Shekhar,
B.B.V., J. Org. Chem., 1992, 57, 4019.
(10) (a) Pandey, G.; Soma Sekhar, B.B.V. J. Chem. Soc. Chem.
Commun. 1993, 1636. (b) Pandey, G.; Soma Sekhar, B.B.V.,
Tetrahedron, 1995, 51, 1483.
(11) For a recent syn-addition approach to trans-2,5-dialkyl
tetrahydrofuran, see Towne, T.B.; McDonald, F.E. J. Am.
Chem. Soc. 1997, 119, 6022.
(12) For direct addition of a nucleophile to a radical-cation
possessing stabilising functionalities, see Reitstoen, B.;
Parker, V. D. J. Am. Chem. Soc. 1991, 113, 6954.
(13) Representative 1H NMR and 13C NMR data of cyclic ethers:
Compound 5; 1H NMR (200 MHz, CDCl3): δ 7.53 (4H, m),
7.33 (6H, m), 4.31 (1H, m), 4.17 (1H, m), 3.16 (2H, m), 3.01
(2H, m), 2.15 (2H, m), 1.76 (2H, m). 13C NMR (50 MHz,
CDCl3): δ 132.58, 132.49, 130.92, 129.43, 129.09, 126.65,
79.18, 78.70, 33.20, 32.13, 31.26. Compound 12: 1H NMR
(200 MHz, CDCl3) δ 7.60 (4H, m), 7.25 (6H, m), 3.90 (1H,
m), 3.75 (3H, m), 3.55 (1H, dd, J = 5.3, 11.2 Hz), 3.05 (4H,
m), 2.73 (1H, dd, J = 5.3, 11.2 Hz). 13C NMR (50 MHz,
CDCl3) δ 133.32, 133.15, 129.50, 127.48, 75.54, 70.61, 70.38,
69.50, 28.68, 28.32. Compound 14: 1H NMR (200 MHz,
CDCl3) δ 7.50 (2H, m), 7.24 (3H, m), 4.08 (1H, m), 3.88 (1H,
m), 3.71 (1H, m), 3.08 (1H, dd, J = 7.2, 12.9 Hz), 2.95 (1H, dd,
J = 7.2, 12.9 Hz), 2.05 (2H, m), 1.87 (2H, m), 1.59 (2H, m),
1.87 (3H, bs). 13C NMR (50 MHz, CDCl3) δ 132.77, 130.56,
129.24, 127.03, 78.55, 68.56, 33.26, 31.75, 26.17.
(14) (a) Pandey, G.; Soma Sekhar, B.B.V.; Bhalerao, U.T. J.Am.
Chem. Soc. 1990, 112, 5650. (b) Pandey. G.; Soma Sekhar,
B.B. V. J. Org. Chem. 1994, 59, 7367.
In order to establish the generality of this reaction, number
of substrates (6–10) were studied and the results are sum-
marized in the Table. The α,α′-trans-dialkyl stereochem-
istry in each product was established, beyond doubt, by
detailed spectral analyses.13 In each case, the products
were isolated in the diselenylated form except for 9 where
monodeselenylated product 14 was obtained, obviously,
by the further oxidative PET cleavage of -C-Se- bond as
reported by us earlier.14
In conclusion, a novel strategy involving atom economy
concept15 has been developed for the synthesis of α,α′-
trans cyclic ethers by the oxyselenylation of dienes utiliz-
ing in situ generated electrophilic selenium species. Fur-
ther, application of this strategy utilizing optically active
diaryldiselenide is in progress .
(15) (a) Trost, B.M., Science, 1991, 254, 1471. (b) Trost, B. M.
Angew. Chem. Int. Ed. Eng. 1995, 34, 259.
Article Identifier:
1437-2096,E;1999,0,08,1257,1258,ftx,en;L06799ST.pdf
Synlett 1999, No. 8, 1257–1258 ISSN 0936-5214 © Thieme Stuttgart · New York