- Reversal of enantioselectivity on protonation of enol(ate)s derived from 2-methyl-1-tetralone using C2-symmetric sulfonamides
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The synthesis of enantiomerically enriched (R)-2-methyl-1-tetralone 1 (64% e.e.) was achieved through protonation of its lithium enolate 3 using a C 2-symmetrical bis-sulfonamide 5d as an internal proton source. Access to the complementary (S)-enantiomer 1 (45% e.e.) can be achieved using an external quench strategy involving acetic acid as the external proton source.
- Boyd, Ewan,Coumbarides, Gregory S.,Eames, Jason,Hay, Alastair,Jones, Ray V.H.,Stenson, Rachel A.,Suggate, Michael J.
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- Synthesis of C2-symmetric aza- And azaoxa-macrocyclic ligands derived from (1R,2R)-1,2-diaminocyclohexane and their applications in catalysis
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Investigations have been undertaken into the synthesis of chiral derivatives of 1,4,7-triazacyclononane and 1,7-diaza-4-oxacyclononane that incorporate the C2-symmetric (R,R)-1,2-diaminocyclohexane backbone. The target ligands 17a and 17b have been prepared as their hydrochloride salts, the latter of which has been characterized by single crystal X-ray diffraction revealing an extensively hydrogen bonded polymeric network in the solid state. These investigations have shown that the formation of the fused bicyclic system in these ligands via standard Richman-Atkins macro-cyclisation conditions is extremely difficult, particularly for the intermediate 16a, when three tosyl amide nitrogen atoms must be accommodated in the macrocyclic ring. In addition to these target ligands the unexpected piperazine 15 as well as the novel binucleating ligand 19 have also been prepared. Preliminary investigation into the coordination chemistry of 17b resulted in the formation of the copper(II) complex [Cu(17b)Cl2] in which the copper centre exists in the expected square-pyramidal geometry with the two chloride ions and the nitrogen donors occupying the equatorial positions and with the oxygen donor apically situated. The complex has been screened for activity and found to be a potent catalyst for two hetero-Diels-Alder reactions. The first aza-Diels-Alder reaction of imine 20 with Danishefsky's diene 21 proceeds to yield the cycloadduct 22 in 94% yield. The second nitroso-Diels-Alder reaction relies on the in situ oxidation of hydroxylamine 23 to dienophile 24, catalysed by the complex in the presence of tert-butyl hydroperoxide, which is then trapped as cycloadduct 25 by cyclohexadiene in 69% yield. The Royal Society of Chemistry 2003.
- Pulacchini, Sonia,Sibbons, Kevin F.,Shastri, Kirtida,Motevalli, Majid,Watkinson, Michael,Wan, Hayley,Whiting, Andrew,Lightfoot, Andrew P.
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- Palladium-Catalyzed Modular Synthesis of Substituted Piperazines and Related Nitrogen Heterocycles
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We report here a novel method for the modular synthesis of highly substituted piperazines and related bis-nitrogen heterocycles via a palladium-catalyzed cyclization reaction. The process couples two of the carbons of a propargyl unit with various diamine components to provide nitrogen heterocycles in generally good to excellent yields and high regio- and stereochemical control. (Chemical Equation Presented).
- Montgomery, Thomas D.,Rawal, Viresh H.
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supporting information
p. 740 - 743
(2016/03/01)
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- MgBr2-promoted enantioselectIVe aryl addition of ArTi(OiPr)3 to ketones catalyzed by a titanium(IV) catalyst of N,N′-sulfonylated (1R,2R)-cyclohexane-1,2-diamine
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MgBr2-promoted asymmetric addition of ArTi(OiPr)3 to ketones catalyzed by a titanium catalyst of N,N′-sulfonylated (1R,2R)-cyclohexane-1,2-diamines is reported, and results showed that the chiral N,N′-sulfonylated cyclohex
- Shu, Chao-Chi,Zhou, Shuangliu,Gau, Han-Mou
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p. 98391 - 98398
(2015/12/04)
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- A study of base-catalyzed aldol reaction of trimethylsilyl enolates
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Mukaiyama-type aldol reaction of trimethylsilyl enolates with aldehydes in the presence of a base is a complicated reaction. It usually results in various products determined by the nature of base and reaction medium. The present study has been undertaken to understand these factors and design new Lewis base catalysts to optimize the yield of desired aldol product. It has been shown that mild Bronsted base with inbuilt hydrogen bonding sites are efficient catalysts for the reactions involving trimethylsilyl enolates. Based on the observed results, a mechanism is proposed to explain the reaction outcome.
- Sutar,Joshi
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p. 1553 - 1560
(2015/02/02)
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- Chiral primary amine tagged to ionic group as reusable organocatalyst for asymmetric Michael reactions of C-nucleophiles with α,β-unsaturated ketones
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The first primary amine-derived organocatalyst modified with an ionic group for asymmetric Michael reactions of C-nucleophiles with α,β- unsaturated ketones was synthesized. In the presence of this catalyst and an acidic co-catalyst (AcOH), hydroxycoumarin and its sulfur-containing analogue reacted with benzylideneacetone derivatives or cyclohexenone to afford the corresponding Michael adducts in high yields (up to 97%) and with reasonable enantioselectivity (up to 80%). The catalyst could be easily recovered and efficiently reused three times, afterwards, its activity and stereodifferentiating ability gradually declined. The analysis of recovered catalyst samples by ESI-MS allowed us to detect undesirable side reactions that poisoned the catalyst, and propose an approach for its reactivation. Copyright
- Kucherenko, Alexander S.,Siyutkin, Dmitry E.,Nigmatov, Albert G.,Chizhov, Alexander O.,Zlotin, Sergei G.
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supporting information
p. 3078 - 3086
(2013/01/15)
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- Investigation of macrocyclisation routes to 1,4,7-triazacyclononanes: Efficient syntheses from 1,2-ditosylamides
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Two routes to the synthesis of a cyclohexyl-fused 1,4,7-triazacyclononane involving macrocyclisations of tosamides have been investigated. In the first approach, using a classic Richman-Atkins-type cyclisation of a cyclohexyl-substituted 1,4,7-tritosamide
- Stones, Graham,Tripoli, Regis,McDavid, Colin L.,Roux-Duplgtre, Kewin,Kennedy, Alan R.,Sherrington, David C.,Gibson, Colin L.
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p. 374 - 384
(2008/10/09)
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- Chiral bis(N-sulfonylamino)phosphine- and TADDOL-phosphite-oxazoline ligands: Synthesis and application in asymmetric catalysis
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A series of N,P-ligands has been prepared, containing a chiral oxazoline ring and as a second chiral unit a bis(N-sulfonylamino)phosphine group embedded in a diazaphospholidine ring or a cyclic phosphite group derived from TADDOL. These modular ligands are readily synthesized from chiral amino alcohols and chiral 1,2-diamines or TADDOLs. Palladium and iridium complexes derived from these ligands were found to be efficient catalysts for enantioselective allylic alkylation and olefin hydrogenation, respectively.
- Hilgraf, Robert,Pfaltz, Andreas
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- Synthesis and some octahedral complexes of a chiral triaza macrocycle
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The chiral and bulky tacn (1,4,7-triazacyclononane, L1) analogue chtacn (2,5,8-triazabicyclo[7.4.01,9]tridecane, L2), which has a cyclohexane ring fused to the tacn framework, has been synthesized commencing with (±), (+)-
- Golding, Simon W.,Hambley, Trevor W.,Lawrance, Geoffrey A.,Luther, Stephan M.,Maeder, Marcel,Turner, Peter
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p. 1975 - 1980
(2007/10/03)
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- Chemoenzymatic syntheses of two optically active hexa-azamacrocycles
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Two optically active hexa-azamacrocycles with C2 and D2 symmetry, respectively, have been efficiently synthesized from the enzymatically prepared (R,R)-cyclohexane-1,2-diamine bis(amidoester) derivative (R,R)-4.
- Alfonso, Ignacio,Rebolledo, Francisca,Gotor, Vicente
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p. 367 - 374
(2007/10/03)
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- Katalytische asymmetrische Aminohydroxylierung (AA) von Olefinen
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Keywords: β-Aminoalkohole; Asymmetrische Aminohydroxylierung; Chloramin T; Osmiumverbindungen; Taxolseitenkette
- Li, Guigen,Chang, Han-Ting,Sharpless, K. Barry
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p. 449 - 452
(2007/10/03)
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- Stereoselective Protonation of Carbanions, 4. Enantioselective Protonation of Lactone Enolates
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The prochiral lithium enolates derived from the five-membered lactones rac-1 and rac-2 were protonated by 37 OH- and 21 NH-chiral proton sources in THF at -78 deg C.The enantioselectivities, determined directly from the reaction mixture by chiral HPLC, ar
- Gerlach, Uwe,Haubenreich, Thomas,Huenig, Siegfried
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p. 1969 - 1980
(2007/10/02)
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- A Catalytic Enantioselective Reaction Using a C2-Symmetric Disulfonamide as a Chiral Ligand: Alkylation of Aldehydes Catalyzed by Disulfonamide-Ti(O-i-Pr)4-Dialkyl Zinc System
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Excellent enantioselective alkylation of aldehydes with dialkylzinc has been developed.This methodology is based on the concept of modifying the Lewis acid with a C2-symmetric, electron-withdrawing disulfonamide.The chiral Lewis acid catalysts used in the present study are the titanium complexes, prepared in-situ from disulfonamide and Ti(O-i-Pr)4.Key Words: Chiral disulfonamide; chiral titanium complex; enantioselective alkylation; dialkyl zinc; catalytic reaction
- Takahashi, Hideyo,Kawakita, Takashi,Ohno, Masaji,Yoshioka, Masato,Kobayashi, Susumu
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p. 5691 - 5700
(2007/10/02)
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