- Pivaloylmetals (tBu-COM: M=Li, MgX, K) as equilibrium components
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Short-lived pivaloylmetals, (H3C)3C-COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu2 from the overcrowded metal alkoxides tBuC(=O)-C(-OM)tBu2 (M=MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu-COM by O=C(tBu)-C(CD3)3 with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu-COM species "dimerize" to give the enediolates MO-C(tBu)=C(tBu)-OM along with O=CtBu2 (2 equiv). A common-component rate depression by surplus O=CtBu2 proves the existence of some free tBu-COM (separated from O=CtBu2); but companion intermediates with the traits of an undissociated complex such as tBu-COM & O=CtBu2 had to be postulated. The slow fission step generating tBu-COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu-COLi and tBu-COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu2 by H3CLi or PhCH2K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu-COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product-forming dimerization. Both tBu-COLi and tBu-COK form tBu-CH=O with HN(SiMe3)3, but only tBu-COK is basic enough for being protonated by the precursor acyloin tBuC(=O)-C(-OH)tBu2. Copyright
- Knorr,Boehrer,Schubert,Boehrer
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supporting information; experimental part
p. 7506 - 7515
(2012/07/27)
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- Catalytic intermolecular hetero-dehydro-diels-alder cycloadditions: Regioand diasteroselective synthesis of 5,6-dihydropyridin-2-ones
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A novel catalyzed intermolecular heterodehydro-Diels-Alder reaction between push-pull 1,3-dien-5-ynes and aldimines or silylaldimines is reported. The sequence is promoted both by gold(I) or silver(I) catalysts and leads to the diastereo- and regioselective formation of 5,6- dihydropyridin-2-ones.
- Fernandez-Garcia, Jesus Manuel,Fernandez-Rodriguez, Manuel A.,Aguilar, Enrique
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supporting information; experimental part
p. 5172 - 5175
(2011/12/04)
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- Novel dithia-aza-norbornanes as 'stiff' bicyclic dithiazines
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Addition of lithiated 4,5-dihydro-1,3,5-dithiazines to in situ generated N-silylimines in THF produces 2-(α-aminoalkyl)dithiazines, which rearrange into 3,5-dithia-1-azabicyclo[2.2.1]heptanes upon aqueous workup. These novel bicyclic dithiazines can in tu
- Kurchan, Alexei N.,Wade, Edmir,Kutateladze, Andrei G.
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p. 1731 - 1733
(2007/10/03)
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- Synthesis of substituted tetrahydroisoquinolines and benzo[d]azepines from phthalan or isochroman and N-silylaldimines
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The 4,4'-di-tert-butylbiphenyl-catalyzed lithiation of phthalan (1a) and isochroman (1b) in THF at 0°C affords the corresponding functionalized benzyllithiums 2, which by reaction with N-silylaldimines yield, after acid-base work-up, the expected amino al
- Foubelo,Gomez,Gutierrez,Yus
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p. 1061 - 1064
(2007/10/03)
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- Convenient Access to Primary Amines by Employing the Barbier-Type Reaction of N-(Trimethylsilyl)imines Derived from Aromatic and Aliphatic Aldehydes
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A new versatile preparation of primary amines via benzylation of aromatic and aliphatic aldimines is described. Sonochemical and traditional methods for generation of the reactive intermediates are compared and contrasted. Competitive reactions were analyzed via free energy relationships to support the proposed alkylative mechanism.
- Gyenes, Ferenc,Bergmann, Kathryn E.,Welch, John T.
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p. 2824 - 2828
(2007/10/03)
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- A REGIO- AND STEREOSELECTIVE SYNTHESIS OF SUBSTITUTED PIPERIDONES
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The new activated 2-aza-1,3-dienes 1 are readily prepared by acylation of N-trimethylsilylimines 3.They react with electrophilic olefins to yield substituted piperidones 4 and 6 with high diastereoselectivity.
- Bayard, Philippe,Ghosez, Leon
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p. 6115 - 6118
(2007/10/02)
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- Preparation of Primary Amines and 2-Azetidinones via N-Trimethylsilyl Imines
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Nonenolizable aldehydes react with lithium bis(trimethylsilyl)amide at ambient temperatures to afford solutions of N-trimethylsilyl aldimines.Treatment of these solutions with Grignard reagents or alkyllithiums followed by an aqueous workup gives primary amines in moderate to excellent yields.Treatment of N-trimethylsilyl aldimines with ester enolates provides an expedient route to 1-unsubstituted 2-azetidinones.
- Hart, David J.,Kanai, Ken-ichi,Thomas, Dudley G.,Yang, Teng-Kuei
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p. 289 - 294
(2007/10/02)
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