- Titanium and Boron Mediated Aldol Reactions of β-Hydroxy Ketones
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The reaction of enolates derived from titanium and boron complexes of β-hydroxy ketones with aldehydes afforded aldol products in good to excellent yields.Whereas the boron mediated reactions gave exclusively anti aldol products derived from the reaction at Cα, the titanium mediated reactions produced primarily syn aldol products from reaction at Cα'.The product selectivites observed in the titanium mediated aldol reactions were highly dependent on the substitution pattern of the starting β-hydroxy ketone.
- Luke, George P.,Morris, Joel
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- Lithium hexamethyldisilazide-mediated enolizations: Influence of triethylamine on E/Z selectivities and enolate reactivities
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Lithium hexamethyldisilazide (LiHMDS) in triethylamine (Et 3N)/toluene is shown to enolize acyclic ketones and esters rapidly and with high E/Z selectivity. Mechanistic studies reveal a dimer-based mechanism consistent with previous studies of
- Godenschwager, Peter F.,Collum, David B.
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supporting information; experimental part
p. 8726 - 8732
(2009/02/02)
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- Stereoselective synthesis of a novel spiroacetal-dihydropyrone related to auripyrone
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A model spiroacetal-dihydropyrone related to that found in auripyrones A and B has been synthesised by a spiroacetalisation dehydration cascade. The route includes an unusual mutual kinetic diastereoselecting aldol reaction combining the key fragments.
- Perkins, Michael V.,Jahangiri, Saba,Taylor, Max R.
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p. 2025 - 2028
(2007/10/03)
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- Stereoselective crossed aldol reaction via boron enolate generated from α-iodoketones and 9-BBN-H
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Boron enolates were in situ generated smoothly by treating α-iodo ketones with 9-BBN-H, and aldols were produced in highly diastereoselective manner by successive reaction with various aldehydes at low temperature.
- Mukaiyama, Teruaki,Imachi, Shouhei,Yamane, Keiko,Mizuta, Masahiro
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p. 698 - 699
(2007/10/03)
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- Stereoselective aldol reaction of α-seleno carbonyl compounds: Preparation of (Z)-α,β-unsaturated carbonyl compounds
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The aldol reaction of the titanium enolates of α-seleno esters in the presence of Ph3P or Ph3PO gave the products with high stereoselectivity favoring the syn isomers. Reaction of α-seleno ketones with TiCl4 in the presence of 2 equiv. of Et3N, and subsequently with aldehydes, gave the aldol products with high syn selectivity. The stereoselectivity in the aldol reaction of 3-pentanone also increased by using an excess amount of Et3N. The aldol products thus obtained from the α-seleno carbonyl compounds could be stereospecifically converted to (Z)-α,β-unsaturated carbonyl compounds by treatment with pyridine. (Z)-Alkylidenecyclopentanones were exclusively formed by treatment of the syn-aldol products with Et3N in the dark.
- Nakamura, Shuichi,Hayakawa, Toshinobu,Nishi, Tatsuya,Watanabe, Yoshihiko,Toru, Takeshi
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p. 6703 - 6711
(2007/10/03)
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- Diastereoselective aldol and reformatsky reactions of α-halo carbonyl compounds and aldehydes mediated by Titanium(II) Chloride
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Highly diastereoselective aldol reactions of α-bromo ketones with several aldehydes were successfully carried out by using a combination of titanium(II) chloride and copper or sodium iodide in dichloromethane-pivalonitrile at low temperature. Similarly, Reformatsky reactions of α-bromo thioester with aliphatic aldehydes proceeded to afford β-hydroxy thioesters in good yields under mild conditions.
- Kagayama,Igarashi,Shiina,Mukaiyama
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p. 2579 - 2585
(2007/10/03)
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- Simple metal alkoxides as effective catalysts for the hetero-aldol-Tishchenko reaction
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(equation presented) This paper reports the utility of simple metal alkoxides for the catalytic, stereoselective hetero-aldol-Tishchenko reaction (eq 1). Choice of metal alkoxide is crucial to achieving high efficiency and stereoselectivity. Whereas NaO-t
- Mascarenhas, Cheryl M.,Duffey, Matthew O.,Liu, Shih-Yuan,Morken, James P.
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p. 1427 - 1429
(2008/02/09)
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- Stereoselective Aldol Reaction Using Titanium Ate Complexes - An Efficient Method For Achieving Anti Aldol Selectivity
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Carbonyl compounds react in the presence of titanium ate complexes in the sense of an aldol reaction.The influence of ligands on controlling stereoselection of syn and anti aldol products of the titanium ate complexes used are described.High yield of anti
- Mahrwald, Rainer
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p. 9015 - 9022
(2007/10/02)
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- Catalytic, Diastereoselective Aldol Reactions Using Titanium(IV) Halides
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The aldol reaction in the presence of titanium halides is described.Good yields of aldols 10-17 were obtained even with only catalytic amounts of titanium tetrafluoride.The reactions were carried out in the absence of a base. - Keywords: Aldol reaction /
- Mahrwald, Rainer
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p. 919 - 922
(2007/10/02)
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- Formation of (Z) Dialkylboron Enolates from Enolsilanes: Stereoconvergent Transmetallation and Diastereoselective Aldol Reactions
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Transmetallation of (E) and (Z) enolsilanes using halodialkylborane (R2BX) reagents provides predominantly the (Z) dialkylboron enolate under mild conditions.These enolates afford high levels of syn selectivity in subsequent aldol reactions.
- Duffy, Joseph L.,Yoon, Tehshik P.,Evans, David A.
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p. 9245 - 9248
(2007/10/02)
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- Ytterbium Trifluoromethanesulfonate Mediated Cross-Aldol Reaction between Ketones and Aldehydes
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The cross-aldol reaction between a ketone and an aldehyde proceeded smoothly with threo diastereoselection favorably mediated by ytterbium trifluoromethanesulfonate and tertiary amine in diethyl ether or in dichloromethane.A ytterbium enolate was trapped
- Fukuzawa, Shin-ichi,Tsuchimoto, Teruhisa,Kanai, Takeshi
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p. 2227 - 2232
(2007/10/02)
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- ENANTIO- AND DIASTEREOSELECTIVE ALDOL REACTIONS OF ACHIRAL ETHYL AND METHYL KETONES WITH ALDEHYDES: THE USE OF ENOL DIISOPINOCAMPHEYLBORINATES.
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Enol diisopinocampheylborinates, derived from achiral ethyl and methyl ketones by enolisation in the presence of tertiary amine bases (iPr2NEt or Et2N), undergo enantio- and diastereoselective aldol reactions with aldehydes.The reagents employed, (+)- and (-)-(Ipc)2BOTf, are easily prepared in enantiomerically pure form in two steps from (-)- and (+)-α-pinene, respectively.The aldol reaction between ethyl ketones and aldehydes using (+)- or (-)-(Ipc)2BOTf/iPr2NEt in dichloromethane gives, via the derived chiral Z-enol borinates, syn-α-methyl-β-hydroxy ketones in good enantiomeric excess (66-93percent ee) and with high diastereoselectivity (>95percent).In contrast, the anti-selective aldol reaction of diethylketone via the isomeric E-enol diisopinocampheylborinate (by enolisation with (-)-(Ipc)2BCl) with methacrolein proceeds with negligible enantioselectivity.Use of both the triflate and chloride reagents in the aldol reaction of methyl ketones with aldehydes gives β-hydroxy ketones in moderate enantiomeric excess (53-78percent ee) with a reversal in the enantioface selectivity of the aldehyde compared to the corresponding ethyl ketone syn aldol.This variable selectivity is interpreted as evidence for the participation of competing chair and boat transition states.Other chiral dialkylboron triflate reagents investigated led to reduced enantioselectivities in diethylketone-aldehyde aldol reactions.
- Paterson, Ian,Goodman, Jonathan M.,Lister, M. Anne,Schumann, Russell C.,McClure, Cynthia K.,Norcross, Roger D.
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p. 4663 - 4684
(2007/10/02)
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- Diastereofacial Selectivity of Enolates
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Results from our research in macrolide total synthesis prompted us to investigate ways of altering the diastereofacial selectivity of enolates without making major changes in the enolates' structure.The variation in the diastereofacial selectivity of enolates 7a-g derived from 3,4-syn-3-alkoxy-2,4-dimethylheptan-5-ones (5a-g) is presented.The parent enolate 7a was si-facial selective, while protecting the 3-hydroxyl group gave enolates that were re-facial selective (7b-g).Thus, without changing any chiral centers or backbone functionality, the diastereofacial selectivity of enolates can be varied or reversed.The implications of this finding to natural products synthesis are discussed.
- McCarthy, Peter A.,Kageyama, Masanori
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p. 4681 - 4686
(2007/10/02)
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- ENANTIOSELECTIVE ALDOL CONDENSATIONS: THE USE OF KETONE BORON ENOLATES WITH CHIRAL LIGANDS ATTACHED TO BORON.
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Aldol condensation between diethylketone and simple aldehydes using (Ipc)2BOTf/iPr2NEt in CH2Cl2 gives syn adducts in good ee (66-90percent) and with high diastereoselectivity (>=90percent).Other chiral dialkylboron triflate reagents examined give lower ees.
- Paterson, Ian,Lister, M. Anne,McClure, Cynthia K.
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p. 4787 - 4790
(2007/10/02)
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- Diastereoselective Aldol Addition Using Boron Trichloride or Alkoxydichloroborane
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Under carefully controlled conditions, boron trichloride or alkoxytrichloroborane/ethyldiisopropylamine in CH2Cl2 can be used to effect diastereoselective aldol additions of ethyl ketones to saturated, α,β-unsaturated, or aromatic aldehydes.The C-C bond formation takes place with relative topicity ul ('syn' configuration of the aldols), in selectivities ranging from 90 to 99percent ds (Tables 1-3).Mechanistic aspects of the reaction are discussed.
- Chow, Hak-Fun,Seebach, Dieter
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p. 604 - 614
(2007/10/02)
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- SYNTHETIC CONTROL LEADING TO CHIRAL COMPOUNDS
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A highly diastereoselective cross aldol reaction is developed using divalent tin enolates formed from stannous trifluoromethanesulfonate and carbonyl compounds.The reaction is extended to a highly enantioselective cross aldol reaction employing chiral dia
- Mukaiyama, Teruaki,Iwasawa, Nobuharu,Stevens, Rodney W.,Haga, Toru
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p. 1381 - 1390
(2007/10/02)
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- ERYTHRO-SELECTIVE ALDOL CONDENSATION VIA ENAMINOSILANES
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In the presence of BF3*OEt2, enaminosilanes derived from acyclic and cyclic ketones have been shown to undergo erythro selective kinetic aldol condensation.
- Ando, Wataru,Tsumaki, Hidetoshi
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p. 1409 - 1412
(2007/10/02)
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- STANNOUS TRIFLATE: A NEW ALDOL REACTION VIA DIVALENT TIN ENOLATES
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Divalent tin enolates formed from stannous triflate and ketones react with carbonyl compounds under mild conditions to give the corresponding aldol products in good yields.In the case of crosscoupling with aldehydes, good to excellent erythro-selectivity
- Mukaiyama, Teruaki,Stevens, Rodney. W.,Iwasawa, Nobuharu
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p. 353 - 356
(2007/10/02)
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- A NEW METHOD FOR THE REGIO- AND STEREOSELECTIVE SYNTHESIS OF ALDOLS FROM α-BROMOKETONE AND CARBONYL COMPOUNDS BY USING METALLIC TIN
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Tin(II) enolates, generated in situ by the oxidative addition of α-bromoketones to metallic tin, react with a variety of carbonyl compounds under mild conditions to give the corresponding aldols in good yields.In the case of reactions of the enolate resul
- Harada, Taira,Mukayiama, Teruaki
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p. 467 - 470
(2007/10/02)
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