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Synlett 2006(12): 1883-1886  
DOI: 10.1055/s-2006-947348
LETTER
© Georg Thieme Verlag Stuttgart · New York

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

Katsukiyo Miura*a, Naoki Fujisawaa, Sayaka Toyoharaa, 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;
Further Information

Publication History

Received 22 April 2006
Publication Date:
24 July 2006 (online)

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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

    References and Notes

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11

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.

12

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.