- Gold-catalyzed alkylation of silyl enol ethers with ortho-alkynylbenzoic acid esters
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Unprecedented alkylation of silyl enol ethers has been developed by the use of ortho-alkynylbenzoic acid alkyl esters as alkylating agents in the presence of a gold catalyst. The reaction probably proceeds through the gold-induced in situ construction of leaving groups and subsequent nucleophilic attack on the silyl enol ethers. The generated leaving compound abstracts a proton to regenerate the silyl enol ether structure.
- Aikawa, Haruo,Kaneko, Tetsuro,Asao, Naoki,Yamamoto, Yoshinori
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scheme or table
p. 648 - 652
(2011/08/03)
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- Acylsilane chemistry. Synthesis of regio- and stereoisomerically defined enol silyl ethers using acylsilanes
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The preparation of enol silyl ethers using a carbonyl addition-Brook rearrangement-elimination sequence was studied. The key intermediate α-silyl-β-X-alkoxides could be prepared in several different ways, including the addition of organolithium or hydride reagents to α-X-acylsilanes (path a, using RM with R = alkyl, aryl, vinyl, alkynyl, silyl, stannyl, phosphinyl, and cyano), the addition of α-X-lithium reagents to acylsilanes (path b, X = phenylthio, phenylsulfonyl), or the addition of silyllithium reagents to α-X-ketones (path c, X = phenylthio, alkoxy). All of the reactions gave complete regiocontrol of silyl enol ether formation, and many gave excellent (>99%) stereocontrol as well. The selectivity of the carbonyl addition, silyl rearrangement, and elimination was studied. For path a, when the R group of RM was a poor carbanion stabilizing group the elimination of the intermediate α-silyl-β-X-alkoxides was stereospecific, and there was a large difference in rate between erythro and threo (erythro > threo). When R was a carbanion stabilizing group, such as aryl or alkynyl, the elimination process became nonstereospecific in some cases, and only small differences between threo and erythro were observed. Path b was especially effective with α-sulfonyl lithium reagents, and these reactions gave predominantly E enol silyl ethers (4/1 to 20/1). The addition of organolithium reagents to β-X-acylsilanes (the homologue of path a) was also briefly explored as a synthesis of siloxy-cyclopropanes.
- Reich, Hans J.,Holtan, Ronald C.,Bolm, Carsten
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p. 5609 - 5617
(2007/10/02)
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- Silyl Ketone Chemistry. Synthesis of Regio- and Stereoisomerically Pure Enol Silyl Ethers Using α-Phenylthio Silyl Ketones
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The addition of a number of organometallic reagents to α-phenylthio silyl ketones proceeds with good to excellent diastereoselectivity.The products undergo Brook rearrangement and fragmentation to enol silyl ethers with, in most cases, excellent stereoche
- Reich, Hans J.,Holtan, Ronald C.,Borkowsky, Samuel L.
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p. 312 - 314
(2007/10/02)
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