Rapid, Selective Ru-Sulfonate-Catalyzed Allylation of Indoles Using Alcohols as Substrates

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• 作者：Stefan Gruber ; Alexey B. Zaitsev ; Michael Wrle ; Paul S. Pregosin ; Luis F. Veiros
• 刊名：Organometallics
• 出版年：2009
• 出版时间：June 22, 2009
• 年：2009
• 卷：28
• 期：12
• 页码：3437-3448
• 全文大小：433K
• 年卷期：v.28,no.12(June 22, 2009)
• ISSN：1520-6041

文摘

The Ru-catalyzed allylation of differing indole compounds using ArCH(OH)CH═CH₂ (Ar = Ph, 2-CH₃C₆H₄, 2-CH₃OC₆H₄ 2-ClC₆H₄, and 1-naphthyl) is relatively fast (usually <30 min for 100% conversion) at ambient temperature in the presence of [Ru(Cp*)(CH₃CN)₃](PF₆) + a sulfonic acid cocatalyst, RSO₃H (R = p-tolyl, a camphor fragment or CH₃). The new catalysts allow allyl alcohols rather than carbonates, halides, acetates, etc., to be used as substrates in this allylation chemistry, thereby avoiding the use of a (wasted) leaving group. The branched products are favored, and in a number of examples b/l ratios in excess of 20 are observed. The catalyst is selective in that there is little or no N-allylation. The use of acids such as CF₃SO₃H or HBF₄ results in slower and/or less selective reactions. Although phosphoric acid additives show some promise, carboxylic acids are much less effective or do not catalyze the reaction at all. The preformed isolated complexes [Ru(Cp*)(η³-C₃H₅)(RSO₃)₂] are efficient catalyst precursors; however, NMR experiments suggest that one of the active species is the monosulfonate cationic complex [Ru(Cp*)(η³-C₃H₅)(CH₃CN)(RSO₃)]⁺. Stoichiometric oxidative addition reactions are shown to be relatively rapid. New Ru(Cp*) complexes have been generated and characterized by NMR methods. DFT calculations suggest that the large b/l ratios observed have a structural basis in that the Ru−C(allyl) bond length for the substituted terminal allyl carbon, Ru−C(1), is relatively long. X-ray structures for Ru(Cp*)(η³-C₃H₅)(SO₄) and the dication [Ru(Cp*)(η³-C₃H₅)(H₂O)₂]²⁺ (as a camphor sulfonate salt) are reported.