Indium(III) Salt Promoted Intramolecular Addition of Allylsilanes to Unactivated Alkynes

Katsukiyo Miura; Naoki Fujisawa; Sayaka Toyohara; Akira Hosomi

doi:10.1055/s-2006-947348

LETTER

Indium(III) Salt Promoted Intramolecular Addition of Allylsilanes to Unactivated Alkynes

Katsukiyo Miura*^a, Naoki Fujisawa^a, Sayaka Toyohara^a, Akira Hosomi*^b
^a Department of Chemistry, 21st Century COE, Graduate School of Pure and Applied Sciences, University of Tsukuba, and CREST, Japan Science and Technology Corporation (JST), Tsukuba, Ibaraki 305-8571, Japan
Fax: +81(29)8536503; e-Mail: miura@chem.tsukuba.ac.jp;
^b Faculty of University Evaluation and Research, National Institution for Academic Degrees and University Evaluation, Kodaira, Tokyo 187-8587, Japan
e-Mail: hosomi@chem.tsukuba.ac.jp;

Abstract

All articles of this category

Abstract

In the presence of a stoichiometric or catalytic amount of a Lewis acidic indium(III) salt, allylsilanes reacted intramolecularly with unactivated terminal alkynes to give cyclized products in good to high yields. The fact that the reaction proceeded in a trans-addition mode suggests a reaction mechanism via electrophilic activation of the triple bond by the indium salt.

Key words

alkynes - catalysis - cyclizations - indium - silicon

Full Text

References

References and Notes

<A NAME="RU04606ST-1A">1a</A> Miura K. Hosomi A. In Main Group Metals in Organic Synthesis Vol. 2: Yamamoto H. Oshima K. Wiley-VCH; Weinheim Germany: 2004. Chap. 10. p.409

<A NAME="RU04606ST-1B">1b</A> Hosomi A. Acc. Chem. Res. 1988, 21: 200

For Lewis acid promoted allylsilylations of alkynes and alkenes, see:

<A NAME="RU04606ST-2A">2a</A> Yamamoto Y. Asao N. Bull. Chem. Soc. Jpn. 2000, 73: 1071

<A NAME="RU04606ST-2B">2b</A> Jung IN. Yoo BR. Synlett 1999, 519

<A NAME="RU04606ST-3">3</A> Yamaguchi M. Sotokawa T. Hirama M. Chem. Commun. 1997, 743

<A NAME="RU04606ST-4">4</A> Miura K. Saito H. Nakagawa T. Hondo T. Tateiwa J. Sonoda M. Hosomi A. J. Org. Chem. 1998, 63: 5740

<A NAME="RU04606ST-5A">5a</A> Fernández-Rivas C. Méndez M. Echavarren AM. J. Am. Chem. Soc. 2000, 122: 1221

<A NAME="RU04606ST-5B">5b</A> Fernández-Rivas C. Méndez M. Nieto-Oberhuber C. Echavarren AM. J. Org. Chem. 2002, 67: 5197

<A NAME="RU04606ST-5C">5c</A> Méndez M. Echavarren AM. Eur. J. Org. Chem. 2002, 15

<A NAME="RU04606ST-6">6</A> Miura K. Fujisawa N. Hosomi A. J. Org. Chem. 2004, 69: 2427

<A NAME="RU04606ST-7A">7a</A> Fugami K. Oshima K. Utimoto K. Nozaki H. Bull. Chem. Soc. Jpn. 1987, 60: 2509

The original method, in which CuCN was not used, resulted in low reproducibility. Use of the copper catalyst achieved high yield of the desired adduct with good reproducibility.

<A NAME="RU04606ST-8">8</A> The competitive desilylation is attributable to higher nucleophilicity of the methallylsilane moiety. See: Hagen G. Mayr H. J. Am. Chem. Soc. 1991, 113: 4954

The formation of Me₃SiOTf is expected in the In(OTf)₃-promoted reaction (Scheme [3] ). A strong Brønsted acid generated by reaction of In(OTf)₃ or Me₃SiOTf with adventitious water [e.g., TfOH, H₂O·In(OTf)₃] would cause the competitive desilylation. In the case of InCl₃, its moderate Lewis acidity and water-tolerance may suppress the generation of a strong Brønsted acid causing the desilylation, see ref. 9b. Me₃SiCl, a by-product, can be a source of HCl, which has enough ability to desilylate allylsilanes. However, hydrolysis of Me₃SiCl is expected to be slower than that of Me₃SiOTf, a strong Lewis acid. The slow generation of HCl from Me₃SiCl may allow the efficient cyclization of 1e with InCl₃.

<A NAME="RU04606ST-9B">9b</A> Babu SA. Synlett 2002, 531

For synthetic reactions involving electrophilic activation of alkynes by an indium salt, see:

<A NAME="RU04606ST-10A">10a</A> Tsuchimoto T. Maeda T. Shirakawa E. Kawakami Y. Chem. Commun. 2000, 1573

<A NAME="RU04606ST-10B">10b</A> Tsuchimoto T. Hatanaka K. Shirakawa E. Kawakami Y. Chem. Commun. 2003, 2454

<A NAME="RU04606ST-10C">10c</A> Tsuchimoto T. Matsubayashi M. Kaneko M. Shirakawa E. Kawakami Y. Angew. Chem. Int. Ed. 2005, 44: 1336

<A NAME="RU04606ST-10D">10d</A> Sakai N. Annaka K. Konakahara T. Org. Lett. 2004, 6: 1527

<A NAME="RU04606ST-10E">10e</A> Takita R. Fukuta Y. Tsuji R. Ohshima T. Shibasaki M. Org. Lett. 2005, 7: 1363

In the InCl₃-promoted reaction of allylstannanes (Scheme [1] and ref. 6), a similar vinylindium species survived under almost the same conditions, and could be deuterated with good D-content. The present InCl₃-promoted reaction should form Me₃SiCl as well as the cyclized products. Me₃SiCl is more sensitive toward hydrolysis than Bu₃SnCl, a by-product of the reaction of allylstannanes. HCl generated from Me₃SiCl and adventitious water may cause the in situ protonation of vinylindium 4.

We tried the In(OTf)₃-promoted reaction of 1a using CaH₂ (1 equiv) as a dehydration agent; however, treatment of the reaction mixture with DCl-D₂O resulted in low D-content (<5%) of 2a.