Tõnis Kanger - Academia.edu (original) (raw)
Papers by Tõnis Kanger
ChemInform, Aug 12, 2010
Enantioselective ortho-Lithiation of Benzaldehyde Chromiumtricarbonyl Complex.-The asym. ortho li... more Enantioselective ortho-Lithiation of Benzaldehyde Chromiumtricarbonyl Complex.-The asym. ortho lithiation of benzaldehyde chromiumtricarbonyl is performed by in situ temporary protection of the aldehyde functionality with a chiral amide (I)-(IV) and BuLi as metallating agent. The reaction with an electrophile MeI followed by acidic hydrolysis leads to the enantiomerically enriched ortho substituted benzaldehyde chromiumtricarbonyl as the major product. Best results are obtained using the chiral diamine (Ia) which gives exclusively the ortho methylated (R)-and (S)-enantiomers (6:1) in 68% yield with 72% e.e. The diamine (Ib) also gives a good enantioselectivity for the (R)-enantiomer (78% e.e.), but a lower regioselectivity (ortho: meta + para = 3:1).
Synthesis, Oct 1, 2015
A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-un... more A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an allcarbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group.
ChemInform, Jun 11, 2012
Ether (I) readily reacts with α,β-unsaturated aldehydes to give the adducts (III) as 1,2-diketone... more Ether (I) readily reacts with α,β-unsaturated aldehydes to give the adducts (III) as 1,2-diketone structural subunits with good e.e.values after reductive work-up and deprotection (no details for step 2 and 3 accessible).
Tetrahedron-asymmetry, Nov 1, 2002
Ti(OiPr) 4 /diethyl tartrate/tBuOOH system oxidizes 3-alkyl-1,2-cyclopentanediones resulting in h... more Ti(OiPr) 4 /diethyl tartrate/tBuOOH system oxidizes 3-alkyl-1,2-cyclopentanediones resulting in hydroxylated ring cleavage products 2-alkyl-g-lactone acids, in high enantioselectivity (95% ee) and satisfactory isolated yields (up to 55%).
Journal of Organic Chemistry, Apr 9, 2009
A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-un... more A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an allcarbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group.
Beilstein Journal of Organic Chemistry, Feb 3, 2022
An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied... more An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied in the presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities.
ChemInform, Jun 7, 2010
Synthesis of the AB-Ring of 9,11-Secosterols.-The synthesis of the A,B-ring title compounds (IX) ... more Synthesis of the AB-Ring of 9,11-Secosterols.-The synthesis of the A,B-ring title compounds (IX) is reported for the first time starting from (S)-Wieland-Miescher ketone (I). Three new stereocenters are introduced with high diastereoselectivity by consecutive stereoselective hydride reductions, double bond isomerization, and stereoselective hydroboration.
ChemInform, Aug 22, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Journal of Organic Chemistry, Jan 22, 2010
A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficie... more A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficient catalyst for the enantioselective Henry reaction. The easy availability of both catalyst components, mild reaction conditions, high yield, and good to excellent enantioselectivity make the catalyst useful for everyday practice.
Asymmetric Organocatalysis, Nov 18, 2022
ChemInform, Dec 22, 2014
Sonogashira Cross-Coupling of Arenediazonium Salts.-The title compounds are alkynylated by a domi... more Sonogashira Cross-Coupling of Arenediazonium Salts.-The title compounds are alkynylated by a domino iododediazoniation/Sonogashira cross-coupling using various terminal alkynes and a variety of functionalities is tolerated for both types of substrates. Synthesis of the arenediazonium salts and the iododediazoniation/Sonogashira cross-coupling sequence can also be performed as a one-pot process [cf. (IIId,e)]. 2-Phenylindole (X) is successfully prepared by subsequent treatment of (IX) with NaAuCl4.-(FABRIZI, G.
ChemInform, Aug 4, 2010
Asymmetric Baeyer-Villiger Reaction: Diastereodifferentiating Peracid Oxidation of Chiral Acetal ... more Asymmetric Baeyer-Villiger Reaction: Diastereodifferentiating Peracid Oxidation of Chiral Acetal in the Presence of Lewis Acid.-Oxidation of acetals, derived from prochiral cyclobutenones and an optically active C2 symmetric diol, using peracid in the presence of Lewis acid provides optically active lactones. The enantiomeric excess depends on the solvent, the chiral diol, the Lewis acid and its amount, and the temperature (79% e.e. for (III) if the reaction is carried out at-78 • C).-(SUGIMURA, T.;
ChemInform, Aug 12, 2010
Enantioselective ortho-Lithiation of Benzaldehyde Chromiumtricarbonyl Complex.-The asym. ortho li... more Enantioselective ortho-Lithiation of Benzaldehyde Chromiumtricarbonyl Complex.-The asym. ortho lithiation of benzaldehyde chromiumtricarbonyl is performed by in situ temporary protection of the aldehyde functionality with a chiral amide (I)-(IV) and BuLi as metallating agent. The reaction with an electrophile MeI followed by acidic hydrolysis leads to the enantiomerically enriched ortho substituted benzaldehyde chromiumtricarbonyl as the major product. Best results are obtained using the chiral diamine (Ia) which gives exclusively the ortho methylated (R)-and (S)-enantiomers (6:1) in 68% yield with 72% e.e. The diamine (Ib) also gives a good enantioselectivity for the (R)-enantiomer (78% e.e.), but a lower regioselectivity (ortho: meta + para = 3:1).
Synthesis, Oct 1, 2015
A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-un... more A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an allcarbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group.
ChemInform, Jun 11, 2012
Ether (I) readily reacts with α,β-unsaturated aldehydes to give the adducts (III) as 1,2-diketone... more Ether (I) readily reacts with α,β-unsaturated aldehydes to give the adducts (III) as 1,2-diketone structural subunits with good e.e.values after reductive work-up and deprotection (no details for step 2 and 3 accessible).
Tetrahedron-asymmetry, Nov 1, 2002
Ti(OiPr) 4 /diethyl tartrate/tBuOOH system oxidizes 3-alkyl-1,2-cyclopentanediones resulting in h... more Ti(OiPr) 4 /diethyl tartrate/tBuOOH system oxidizes 3-alkyl-1,2-cyclopentanediones resulting in hydroxylated ring cleavage products 2-alkyl-g-lactone acids, in high enantioselectivity (95% ee) and satisfactory isolated yields (up to 55%).
Journal of Organic Chemistry, Apr 9, 2009
A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-un... more A novel enantioselective (up to 90% ee) Michael addition of a-substituted cyanoacetates to a,b-unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an allcarbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group.
Beilstein Journal of Organic Chemistry, Feb 3, 2022
An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied... more An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied in the presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities.
ChemInform, Jun 7, 2010
Synthesis of the AB-Ring of 9,11-Secosterols.-The synthesis of the A,B-ring title compounds (IX) ... more Synthesis of the AB-Ring of 9,11-Secosterols.-The synthesis of the A,B-ring title compounds (IX) is reported for the first time starting from (S)-Wieland-Miescher ketone (I). Three new stereocenters are introduced with high diastereoselectivity by consecutive stereoselective hydride reductions, double bond isomerization, and stereoselective hydroboration.
ChemInform, Aug 22, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Journal of Organic Chemistry, Jan 22, 2010
A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficie... more A complex derived from the enantiomeric bipiperidine and copper(II) acetate hydrate is an efficient catalyst for the enantioselective Henry reaction. The easy availability of both catalyst components, mild reaction conditions, high yield, and good to excellent enantioselectivity make the catalyst useful for everyday practice.
Asymmetric Organocatalysis, Nov 18, 2022
ChemInform, Dec 22, 2014
Sonogashira Cross-Coupling of Arenediazonium Salts.-The title compounds are alkynylated by a domi... more Sonogashira Cross-Coupling of Arenediazonium Salts.-The title compounds are alkynylated by a domino iododediazoniation/Sonogashira cross-coupling using various terminal alkynes and a variety of functionalities is tolerated for both types of substrates. Synthesis of the arenediazonium salts and the iododediazoniation/Sonogashira cross-coupling sequence can also be performed as a one-pot process [cf. (IIId,e)]. 2-Phenylindole (X) is successfully prepared by subsequent treatment of (IX) with NaAuCl4.-(FABRIZI, G.
ChemInform, Aug 4, 2010
Asymmetric Baeyer-Villiger Reaction: Diastereodifferentiating Peracid Oxidation of Chiral Acetal ... more Asymmetric Baeyer-Villiger Reaction: Diastereodifferentiating Peracid Oxidation of Chiral Acetal in the Presence of Lewis Acid.-Oxidation of acetals, derived from prochiral cyclobutenones and an optically active C2 symmetric diol, using peracid in the presence of Lewis acid provides optically active lactones. The enantiomeric excess depends on the solvent, the chiral diol, the Lewis acid and its amount, and the temperature (79% e.e. for (III) if the reaction is carried out at-78 • C).-(SUGIMURA, T.;