- Synthesis of E-α,β-unsaturated ketones with complete stereoselectivity via sequential aldol-type/elimination reactions promoted by samarium diiodide or chromium dichloride
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E-α,β-Unsaturated ketones can be obtained with complete E-selectivity by a sequential reaction of dichloroketones with a variety of aldehydes. This transformation was promoted by SmI2, SmI2 in the presence of FeCl3 or CrCl2. The best results were obtained when CrCl2 was used as the metallating agent. A mechanism based on a successive aldol-type reaction and a β-elimination is proposed to explain these results. Georg Thieme Verlag Stuttgart.
- Concellón, José M.,Rodríguez-Solla, Humberto,Concellón, Carmen,Díaz, Pamela
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- Aldol reactions of α-bromoalkyl phenyl ketones and aldehydes with tin(IV) iodide and tetrabutylammonium iodide
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Aldol reactions of α-bromoacetophenone and aldehydes in dichloromethane produced the corresponding E-α,β-unsaturated ketones at 25 °C with one equimolar amount of tin(IV) iodide, one equimolar amount of tetrabutylammonium iodide and one equimolar amount of N,N- diisopropylethylamine, and produced the corresponding β-hydroxy ketones at -80 °C with one equimolar amount of tin(IV) iodide and two equimolar amounts of tetrabutylammonium iodide. Using one equimolar amount of tin(IV) iodide and two equimolar amounts of tetrabutylammonium iodide at -80 °C in dichloromethane, α-bromopropiophenone reacted with aldehydes to afford the corresponding syn-α-methyl-β-hydroxy ketones selectively. Georg Thieme Verlag Stuttgart.
- Masuyama, Yoshiro,Ohtsuka, Masaru,Kondo, Ayako
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p. 3346 - 3348
(2008/09/18)
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- An efficient synthesis of (E)-α,β-unsaturated ketones and esters with total stereoselectivity by using chromium dichloride
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(E)-α,β-Unsaturated ketones 1 or esters 2 can be obtained with complete stereoselectivity by reaction of different 2-chloro-3-hydroxy ketones 3 or esters 4 and CrCl2. A comparative study of the results of synthesis of ketones 1 with CrCl2 or samarium is performed. A mechanism to explain both β-elimination reactions has been proposed.
- Concellón, José M.,Rodríguez-Solla, Humberto,Méjica, Carmen
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p. 3292 - 3300
(2007/10/03)
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- Asymmetric Michael reactions of aminocarbene complex anions
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The first Michael addition reactions of the anions of aminocarbene complexes to αβ-unsaturated carbonyl compounds are reported. Unlike their corresponding amide enolates, these anions give exclusive 1,4-addition to a number of enones. For chiral complex 27, it was shown that the formation of the 1,4-addition product is not reversible and that the initial 1,4-addition is thus kinetically controlled. The anions of aminocarbene complexes are much more effective in this regard than the anions of alkoxycarbene complexes. It was demonstrated that aminocarbene complexes can serve as synthons for amides in Michael additions since the metal can be liberated from the Michael adducts to give amide products by oxidation with either DMSO or dimethyldioxirane. The steric bulk of the metal unit in the aminocarbene complex anions plays a role in the facial selectivity in the addition to 1,4-diphenyl-2-penten-l-one which produces a 21:1 mixture of diastereomers in the case of methyl pyrrolidino complex 12. This is the highest facial selectivity that has ever been observed in the Michael additions of enolates to this enone. The Michael additions of the chiral amino complex 27 derived from prolinol methyl ether with several cyclic enones were investigated and represents the first examples of asymmetric reactions of any type of the "enolates" of either alkoxy- or amino-stabilized group 6 Fischer carbene complexes. Both enantiopodes of 27 were examined with cyclohexenone and found to give asymmetric induction in the range of 65-75% ee which is comparable with the best induction that has yet been reported for the addition of a chiral acetaldehyde equivalent to cyclohexenone.
- Andersen, Benjamin A.,Wulff, William D.,Rahm, Annette
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p. 4602 - 4611
(2007/10/02)
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- Efficient Wittig-Horner Synthesis of Acyclic α-Enones with an Asymmetric Carbon at the γ-Position Using Barium Hydroxide
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β-Monosubstituted acyclic α-enones with an asymmetric carbon at the γ-position: (E)-(5RS)-5-phenylhex-3-en-2-one, (4a), (E)-(6RS)-2,2-dimethyl-6-phenylhept-4-en-3-one, (4b), (E)-(4RS)-1,4-diphenylpent-2-en-1-one, (4c), (E)-(5RS)-6,6-dimethyl-5-phenylhept-
- Ibarra, Carlos Alvarez,Arias, Selma,Fernandez, Maria J.,Sinisterra, Jose V.
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p. 503 - 508
(2007/10/02)
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- Ba(OH)2 AS CATALYST IN ORGANIC REACTIONS - PART XIX - STRUCTURE-CATALYTIC ACTIVITY RELATIONSHIP IN THE AdN OF SEVERAL YLIDS TO CH=O GROUP, CATALYZED BY ACTIVATED BARIUM HYDROXIDE CATALYST
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The reactivity of several products R1R2CH-X(1+), 1, (X=N,P,S), which can produce ylids by reaction with bases, has been tested using the activated barium hydroxide catalysts, C-200.Wittig-Horner, Wittig, Corey-Chaykovsky and Kroehnke type reactions have been analyzed.The pKa of 1, and the structure of active sites control the process.When 1 has a strong acid character, the process takes place - dissolving the solid - in homogeneous phase.When 1, has pKa values 11.7), that control the reaction mechanism and the reactivity of adsorbed ylids.
- Sinisterra, J. V.,Marinas, J. M.,Riquelme, F.,Arias, M. S.
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p. 1431 - 1440
(2007/10/02)
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