Asymmetric Steering of Oxa Diels–Alder Reactions with Silyloxydienes Employing Proline Esters as Chiral Auxiliary Groups

Bläser, Edwin; Kolar, Patrik; Fenske, Dieter; Goesmann, Hellmut; Waldmann, Herbert

doi:10.1002/(sici)1099-0690(199901)1999:1<329::aid-ejoc329>3.0.co;2-z

Cited by 13 publications

(6 citation statements)

References 26 publications

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“…These values are consistent with the upfield shift for one of the two alkene CHs in both 1 and 2 . Compound 9 in D 2 O has an alkene chemical shift at 6.90 ppm, while 10 in CDCl 3 has two alkene CH chemical shifts observed at 7.29 and 7.08 ppm …”

Section: Resultsmentioning

confidence: 99%

Solution and Solid-State Models of Peptide CH···O Hydrogen Bonds

et al. 2002

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Fumaramide derivatives were analyzed in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography in order to characterize the formation of CH...O interactions under each condition and to thereby serve as models for these interactions in peptide and protein structure. Solutions of fumaramides at 10 mM in CDCl(3) were titrated with DMSO-d(6), resulting in chemical shifts that moved downfield for the CH groups thought to participate in CH...O=S(CD(3))(2) hydrogen bonds concurrent with NH...O=S(CD(3))(2) hydrogen bonding. In this model, nonparticipating CH groups under the same conditions showed no significant change in chemical shifts between 0.0 and 1.0 M DMSO-d(6) and then moved upfield at higher DMSO-d(6) concentrations. At concentrations above 1.0 M DMSO-d(6), the directed CH...O=S(CD(3))(2) hydrogen bonds provide protection from random DMSO-d(6) contact and prevent the chemical shifts for participating CH groups from moving upfield beyond the original value observed in CDCl(3). X-ray crystal structures identified CH...O=C hydrogen bonds alongside intermolecular NH...O=C hydrogen bonding, a result that supports the solution (1)H NMR spectroscopy results. The solution and solid-state data therefore both provide evidence for the presence of CH...O hydrogen bonds formed concurrent with NH...O hydrogen bonding in these structures. The CH...O=C hydrogen bonds in the X-ray crystal structures are similar to those described for antiparallel beta-sheet structure observed in protein X-ray crystal structures.

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Section: Resultsmentioning

confidence: 99%

Solution and Solid-State Models of Peptide CH···O Hydrogen Bonds

et al. 2002

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“…Until now, numerous synthetic approaches have been examined to effect a facile synthesis of this core structure . It is well-known that one of the most convenient methods is hetero-Diels−Alder (HDA) reaction 3 of Brassard's diene 4 with suitable aldehydes or ketones . The scope of the methodology can also be limitlessly expanded when coupled with Winkler's transformation of 4-alkoxy-α,β-unsaturated δ-lactones to 2,3-dihydropyran-4-ones …”

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confidence: 99%

Efficient Enantioselective Hetero-Diels−Alder Reaction of Brassard's Diene with Aliphatic Aldehydes: A One-Step Synthesis of (R)-(+)-Kavain and (S)-(+)-Dihydrokavain

Lin

Chen

et al. 2008

Org. Lett.

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An efficient catalytic asymmetric hetero-Diels-Alder reaction of Brassard's diene with aliphatic aldehydes was reported. The catalyst, which was generated from (R)-BINOL, Ti(i-PrO)4, and 4-picolyl chloride hydrochloride, promoted the reaction smoothly to afford the corresponding alpha,beta-unsaturated delta-lactone derivatives in moderate-to-good yields (46-79%) with high enantioselectivities (up to 88% ee). Natural products (R)-(+)-kavain (70% ee, >99% ee after single recrystallization) and (S)-(+)-dihydrokavain (84% ee) were also prepared in one step by using this methodology.

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“…175 Esters derived from (S)-proline are useful as chiral auxiliaries in a three-component reaction leading to propargylamines, 176 in conjuguate addition 177 and in oxa-Diels-Alder reactions. 178 Proline methyl ester is easily homologated to the corresponding β-amino ester by Kowalski procedure with high yield and clean preservation of the initial optical purity. 179 Derivatization of alcohols to esters by an esterification reaction with N-benzenesulfonyl-(S)proline has been performed for some crystallographic purposes in the total synthesis of palmarumycin and preussomerin natural products.…”

Section: %mentioning

confidence: 99%