Pummerer-type α-functionalization of arylseleninylacetates by treating with trimethylsilyl- or tri-n-butylstannyl-masked nucleophiles and trifluoroacetic anhydride or a Lewis acid

Article abstract of DOI:10.1016/S0040-4039(00)00681-X

Arylseleninylacetates underwent facile α-functionalization on treatment with trimethylsilyl- or tri-n-butylstannyl-masked nucleophiles and trifluoroacetic anhydride (TFAA) or a Lewis acid. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00681-X

Tetrahedron Letters 41 (2000) 4637±4640
Pummerer-type a-functionalization of arylseleninylacetates by
treating with trimethylsilyl- or tri-n-butylstannyl-masked
nucleophiles and tri¯uoroacetic anhydride or a Lewis acid
Kazuaki Shimada,* Yutaka Kikuta, Hiroyuki Koganebuchi, Fumi Yonezawa,
Shigenobu Aoyagi and Yuji Takikawa
Department of Applied Chemistry and Molecular Science, Faculty of Engineering, Iwate University, Morioka,
Iwate 020-8551, Japan
Received 27 March 2000; accepted 21 April 2000
Abstract
Arylseleninylacetates underwent facile a-functionalization on treatment with trimethylsilyl- or tri-n-
butylstannyl-masked nucleophiles and tri¯uoroacetic anhydride (TFAA) or a Lewis acid. # 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: selenoxide; Pummerer rearrangement; a-allylation; allyltrimethylsilane; a-azidation.
Recent interest in the ®eld of organic heteroatom chemistry has been concentrated on heteroatom-
stabilized carbenium ions, and several methods for a-functionalization of alkyl selenides, seleno-
acetals, a-haloselenides, or alkenyl selenides via chemically- or electrochemically-generated selonium
ions A (X=Se) or a-selenocarbenium ions B (X=Se) have been reported to date.1,2 However, the
lability of seleninyl functionalities has caused serious limitation in the synthetic use of selenoxides
in spite of their potentiality as synthetic equivalents of A or B (Scheme 1). It was expected that
selenoxides 23 bearing an alkyl chain on the selenium atom would undergo a-functionalization
via A or B that might be generated through a Pummerer-type reaction,4 by treating 2 with
nucleophilic reagents. In this paper, we would like to describe an a-functionalization of selenoxides
2 by the combined treatment of nucleophiles masked with a trimethylsilyl or a tri-n-butylstannyl
group and tri¯uoroacetic anhydride (TFAA) or a Lewis acid.
A CH2Cl2 solution of selenide 1a±b was at ®rst treated with mCPBA (1.1 mol amt.) through
the usual procedure to give selenoxides 2a±b as 1:1 epimeric mixtures.3,5 Unexpectedly, treatment
of 1c or 1d with mCPBA only gave the recovery of the compounds in almost quantitative yield
due to deoxygenation during the usual reductive workup (aq. Na2SO3 solution), puri®cation, or
* Corresponding author. Tel: +00-81-19-621-6324; fax: +00-81-19-621-6347; e-mail: shimada@iwate-u.ac.jp
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00681-X

4638
Scheme 1.
storage. These results indicated the e€ective kinetic protection of the seleninyl functionality of 2 by
using the neighboring l-menthyloxycarbonyl moiety. Sulfoxides 4a, 4c, and 4d were also prepared
by similar treatment of sul®des 3 with mCPBA. Subsequently, when a CH2Cl2 solution of 2a or
sulfoxides, 4a, 4c, or 4d, were treated with allyltrimethylsilane or allyltri-n-butylstannane (5, 5.0 mol
.
amt.) and TFAA or BF3 OEt2 (2.2 mol amt.), inseparable diastereomeric mixtures of a-allylation
products, 6a, 8a, 8c, or 8d, respectively, were obtained in modest yields along with 1a or 3 in each
.
case. A similar treatment of 2a with 2-ethoxycarbonylallyltrimethylsilane and BF3 OEt2 also
a€orded 7a predominantly. However, the use of acetic anhydride in place of TFAA for the
reaction of 2a only gave a diastereomeric mixture (about 1:1) of a-acetoxyselenide 14a in 62%
yield. The treatment of 2b with the same reagents or the treatment of 2a with TFAA and an
allylsilane bearing an ethyl or a phenyl group at the g-position only gave a complex mixture. These
results suggested that the steric factor between the g-position (R2) of allylsilanes and the a-position
of the phenylseleninyl group of 2 might a€ect the reaction course. In addition, treatment of a
CH2Cl2 solution of 2a with TFAA in the presence of an additive, such as cyclohexene, phenyl-
acetylene, or anisole, only gave a complex mixture in which no products originated from
electrophilic addition of these adducts were found.1 A similar treatment of 2a or 4c±d with tri-
methylsilyl azide and TFAA also gave a-azidation products, 12a or 13c±d, respectively. All the
results are shown in Tables 1 and 2.
However, one-pot treatment of a CH2Cl2 solution of 1a with mCPBA, allyltrimethylsilane, and
TFAA only gave a complex mixture containing diphenyl diselenide (9), selenide 1a, allyl phenyl
selenide (10), 1-trimethylsilyl-3-phenylseleno-2-propanol (11), and several unidenti®ed products.
1H NMR monitoring of the reaction of a CDCl3 solution of 1a with mCPBA (1.1 mol amt.) at
27ꢀC exhibited the formation of a 1:1 diastereomeric mixture of selenurane X (ꢀ=3.83, 3.85, 4.21,
and 4.25 ppm for the non-equivalent four protons of the methylene groups of X) at the primary
stage.4d,6 However, the signals of X gradually disappeared within several minutes, and new signals
of a diastereomeric mixture of a-acyloxyselenides 15a were observed. Actually, 15a was isolated
as a stable compound and was unreactive toward the a-allylation.
Subsequently, when a CDCl3 solution of 2a was treated with TFAA and the reaction was
monitored by H NMR at 27ꢀC, the formation of bis(tri¯uoroacetoxy)selenurane Y (ꢀ=4.70
1
and 4.75 ppm for the non-equivalent geminal protons of the methylene group of Y) was observed
at the primary stage.6 But, selenurane Y caused facile decomposition within a few minutes into
a-tri¯uoroacetoxyselenide 16a in the CDCl3 solution. Compound 16a seemed stable enough in
the solution but caused facile decomposition to give a complex mixture including 9, 1a, and several
unidenti®ed products, during the usual workup and puri®cation. When a CH2Cl2 solution of 16a,

4639
Table 1
a-Allylation of selenoxides 2 and sulfoxides 4 by treating with an allylating agent 5 and an electrophilic reagent
Table 2
a-Azidation of selenoxide 2a or sulfoxides 4 by treating with trimethylsilyl azide (5) and TFAA
prepared preliminarily by adding TFAA (2 mol amt.) to a CH2Cl2 solution of 2a, was treated
with allyltrimethylsilane (5 mol amt.) at room temperature, only a complex mixture in which
allylation products 6a were found in rather low yield was obtained. These results indicated that
isolation of selenoxides 2 was essentially required for the a-functionalization and that the reactions
might occur only via selonium ions Z (or a-selenocarbenium ions Z0) generated through elimination
of tri¯uoroacetic acid and tri¯uoroacetate ion from Y.3,6 However, several attempts to detect Z
or Z0 by NMR measurements were not successful at all.

4640
In conclusion, a-functionalization of selenoxides 2 was achieved by treating with silyl- or
stannyl-masked nucleophilic reagents and TFAA or Lewis acid through the route including
generation of intermediary selonium ions Z or a-selenocarbenium ions Z0 via selenuranes Y.
Further attempts for the synthetic applications of these reactions are in progress in our laboratory.
Acknowledgements
This work was ®nancially supported in part by a Grant-in-Aid for Scienti®c Research (No.
06650995) from the Ministry of Education, Science, Sports, and Culture of Japan.
References
1. (a) Renard, M.; Hevesi, L. Tetrahedron Lett. 1983, 24, 3911±3912. (b) Silveira, C. C.; Comasseto, J. V.; Catani, V.
Synth. Commun. 1985, 15, 931±937. (c) Hevesi, L. Phosphorus and Sulfur 1988, 38, 191±200. (d) Hevesi, L.; Lavoix,
A. Tetrahedron Lett. 1989, 30, 4433±4434. (e) Hermans, B.; Hevesi, L. Tetrahedron Lett. 1990, 31, 4363±4366. (f)
Hevesi, L. Bull. Soc. Chim. Fr. 1990, 127, 697±703. (g) Silveira, C. C.; Lenardao, E. J.; Comasseto, J. V.;
Dabdoub, M. J. Tetrahedron Lett. 1991, 32, 5741±5744. (h) Hevesi, L. Phosphorus, Sulfur Silicon Relat. Elem.
1992, 67, 155±168. (i) Silveira, C. C.; Araujo, M. A.; Lenardao, E. J.; Braga, A. L.; Dabdoub, M. J. Synthesis
1995, 1305±1310. (j) Hermans, B.; Hevesi, L. J. Org. Chem. 1995, 60, 6141±6147.
2. Surowiec, K.; Fuchigami, T. J. Org. Chem. 1992, 57, 5781±5783.
3. (a) Sharpless, K. B.; Lauer, R. F. J. Am. Chem. Soc. 1973, 95, 2697±2699. (b) Reich, H. J.; Renga, J. M.; Reich,
I. L. J. Am. Chem. Soc. 1975, 97, 5434±5447. (c) Reich, H. J. Acc. Chem. Res. 1979, 12, 22±30 and references cited
therein. (d) Davis, F. A.; Billmers, J. M.; Stringer, O. D. Tetrahedron Lett. 1983, 24, 3191±3194. (e) Kamigata, N.
Yuki Gosei Kagaku Kyokaishi 1990, 48, 229±239 and references cited therein. (f) Reich, H. J.; Yelm, K. E. J. Org.
Chem. 1991, 56, 5672±5679. (g) Kamigata, N.; Shimizu, T. Reviews on Heteroatom Chemistry 1991, 4, 226±248 and
references cited therein. (h) Davis, F. A.; Reddy, R. T. J. Org. Chem. 1992, 57, 2599±2606. (i) Takahashi, T.;
Kurose, N.; Kawanami, S.; Arai, Y.; Koizumi, T.; Shiro, M. J. Org. Chem. 1994, 59, 3262±3264. (j) Bosch, E.;
Kochi, J. K. J. Chem. Soc., Perkin Trans. 1 1996, 2731±2738. (k) Stuhr-Hansen, N.; Sùrensen, H. O.; Henriksen,
L.; Larsen, S. Acta Chem. Scand. 1997, 51, 1186±1191. (l) Shimizu, T.; Enomoto, M.; Taka, H.; Kamigata, N.
J. Org. Chem. 1999, 64, 8242±8247.
4. (a) Sonoda, N.; Miyoshi, N. Tetrahedron Lett. 1977, 851±854. (b) Fujihara, H.; Saito, R.; Yabe, M.; Furukawa, N.
Chem. Lett. 1992, 1437±1440. (c) Uneyama, K.; Tokunaga, Y.; Maeda, K. Tetrahedron Lett. 1993, 34, 1311±1312.
(d) Lowe, W.; Rutjes, T. J. Heterocycl. Chem. 1995, 32, 43±48.
5. Physical data of compounds 1±16 are available as the supplementary materials.
6. (a) Horn, V.; Paetzold, R. Z. Anorg. Allg. Chem. 1973, 398, 186±192. (b) Marino, J. P.; Larsen Jr., R. D. J. Am.
Chem. Soc. 1981, 103, 4642±4643. (c) Uemura, S.; Fukuzawa, S. J. Chem. Soc., Perkin Trans. 1 1985, 471±480. (d)
Tiecco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.; Bartoli, D. Gazz. Chim. Ital. 1987, 117, 423±427. (e) Kurose,
N.; Takahashi, T.; Koizumi, T. Tetrahedron 1997, 53, 12115±12129. (f) Takahashi, T.; Nakano, N.; Koizumi, T.
Tetrahedron: Asymmetry 1997, 8, 3293±3308. (g) Zhang, J.; Kurose, N.; Saito, S.; Takahashi, T.; Koizumi, T. Yuki
Gosei Kagaku Kyokaishi 1999, 57, 587±597 and references cited therein.