Bontront, Jean-Louis J.

Bures, Edward

Hunt, Ian R.

Keay, Brian A

Nieman, James A.

Rauk, Arvi

Spinazzé, Patrick G.

Yu, Shuyuan

PRISM: University of Calgary Digital Repository

Access to full text denied by publisher.  Please contact your local library to acquire the following paper:  Citation:  Regioselective Preparation of 2,4-, 3,4-, and 2,3,4-Substituted Furan Rings. 2.  Regioselective Lithiation of 2-Silylated-3-substituted Furan Rings1 Edward Bures, James A. Nieman, Shuyuan Yu, Patrick G. Spinazzé, Jean-Louis J. Bontront, Ian R. Hunt, Arvi Rauk, and Brian A. Keay pp 8750 – 8759.  Abstract: A new method for the preparation of 3,4- and 2,5-disubstituted furan rings is described. A variety of 2-silylated-3-(hydroxymethyl)furans and 2-silylated-3-furoic acids lithiate exclusively at C-4 when treated with 2.2 equivs of BuLi. The resulting dianions were quenched with a variety of electrophiles to provide 2-silylated-3-(hydroxymethyl)-4-substituted furans and 2-silylated-4-substituted 3-furoic acids in good to excellent yields. Removal of the silyl group (n-Bu4NF) provided a variety of 4-substituted-3-(hydroxymethyl)furans and methyl 4-substituted-3-furoates, respectively. The latter esters were prepared due to difficulties encountered in isolating 4-substituted-3-furoic acids. The site of lithiation was altered by protecting the 3-hydroxyl group with a triethylsilane. Lithiation of 2-silylated-3-(((triethylsilyl)oxy)methyl)furan with 1.2 equivs of BuLi followed by the addition of electrophiles provided 2-silylated-3-(((triethylsilyl)oxy)methyl)-5-substituted furan rings. Subsequent removal of both silyl groups provided 2,4-disubstituted furan rings in moderate to good yields. A rationale is provided to explain why protection of the hydroxyl group at C-3 leads to a change in lithiation from the C-4 to the C-5 position of the furan ring. In addition, an explanation for the observed effect of adding HMPA or LiCl to the solution during the lithiation of 2-(tert-butyldimethylsilyl)-3-(hydroxymethyl)furan is provided.  Tables:            Schemes:                    DOI: 10.1021/jo971098b  

English

Regioselective Preparation of 2,4-, 3,4-, and 2,3,4-Substituted Furan Rings. 2. Regioselective Lithiation of 2-Silylated-3-substituted Furan Rings

Regioselective Preparation of 2,4-, 3,4-, and 2,3,4-Substituted Furan Rings. 2. Regioselective Lithiation of 2-Silylated-3-substituted Furan Rings

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