In the past Wolfgang Oppolzer has collaborated on articles with WOLFGANG OPPOLZER and Jef De Brabander. One of their most recent publications is Asymmetric 1,4-additions of gilman reagents to α,β - disubstitoted (e)-enoylsultams / “enolate” protonations. Which was published in journal Tetrahedron.

More information about Wolfgang Oppolzer research including statistics on their citations can be found on their Copernicus Academic profile page.

Wolfgang Oppolzer's Articles: (17)

Asymmetric 1,4-additions of gilman reagents to α,β - disubstitoted (e)-enoylsultams / “enolate” protonations

AbstractSuccessive treatment of (E)-Cα,Cβ-disubstltuted N-enoyl sultams 6 and 13 with organocopper reagents (Me2CuLi, (CH2CH)2CuLi, Ph2CuLi in the presence of PBu3 or SCN−) and aq. NH4Cl gave products 7 and 14. respectivety, with good to excellent stereoface differentiation at Cβ and Cα. Crystallization and mild saponification 7 → 11 and 14 → 15 furnished enantiomerically pure carboxylic acids containing two new stereogenic centers. The postulated reaction topology is supported via acetylatlon of the transient “nolate” (22 → 23) and compared with that of the related organomagnesium- addition/protonation sequence.


Abstract1Highly enantioselective C,C-bond formation has been achieved in a predictable manner1.1by Lewis-acid-mediated processes such as intramolecular ene-type reactions (synthesis of (+)-α-allokainic acid), bimolecular Diels-Alder- and 1,4-additions using enoates derived from various chiral alcohols followed by regeneration of the auxiliary group;1.2in the “chiral pool”-synthesis of (-)-α-kainic acid from (S)-(-)-glutamic acid via a thermal intramolecular ene reaction, proving the absolute configuration of the neurophysiologically interesting natural products (-)-α-Kainic acid, (-)-α-allokainic acid and domoic acid.2Intramolecular “magnesium-ene” reactions of 2-alkenyl-magnesium chlorides to olefinic bonds have been systematically studied and applied, as illustrated by2.1the development of a reliable and efficient preparation of 2-alkenyl Grignard reagents using slurries of evaporated magnesium;2.2a synthesis of (±)δ9,12-capnellene using an iterative cyclopentane-annulation based on type-I-ene reactions;2.3a synthesis of the unusual sesquiterpene(±)sinularene via a type-I-reaction;2.4regio-and stereochemical studies of unprecedented type-II-reactions;2.5a direct and highly selective synthesis of the olfactively interesting norsesquiterpene (±)-khusimone exploiting a type-II-reaction.

11 - Sultam-directed asymmetric syntheses of α-amino acids

Publisher SummaryEnantiomerically pure α-amino acids are of immense interest not only per se, but also as chiral building blocks and as starting materials for chiral reagents and catalysts. This chapter describes practical routes to this class of compounds via π-face-selective formation of either the Cα-R or Cα-NH2 bond. Convenient sources of chirality are bornane-10,2-sultam, (-)-2 and its antipode (+)-2, accessible from inexpensive (+)- and (-)-camphorsulfonic acids in two simple operations. Both chirophore enantiomers are commercially available in kg-quantities. Addition reactions to N-enoyl derivatives (I), and reactions of enolates (II) with electrophiles, proceed in high yield and with good to excellent π-face discrimination. The chapter also describes that compared to a plethora of auxiliaries so far developed for asymmetric synthesis, sultams are among the most practical and universal.

Enantioselective total synthesis of (−)-denticulatins A and B using a novel group-selective aldolization of a meso dialdehyde as a key step

AbstractThe diastereoselective synthesis of (−)-denticulatin A (1a) was achieved for the first time in 9 steps (41% yield) based on a novel group-selective aldolization of a meso dialdehyde as a key step. The inherent chirality present in bornanesultam 4 was thus transmitted to the five stereocenters spanning C4–C8 in key intermediate 8. In addition, denticulatin B (1b) was obtained from the common intermediate 8 en route to denticulatin A in 10 steps and 35% overall yield.

Enantioselective synthesis and absolute configuration of (−)-pulo'upone by asymmetric intramolecular diels-alder reaction☆

Abstract(−)-Pulo'upone (1) was synthesized via an asymmetric, bornane-10,2-sultam- directed, intramolecular Diels- Alder reaction (3 → 2) and a 2-pyridylcuprate/allylacetate coupling (18 → 1). The (6'R, 9'S, 13'R, 14'R)- configuration of (−)-1 follows from an X-ray diffraction analysis of the cycloaddition product 2.

Efficient asymmetric hydrogenations of camphor-soltam-imide-conjugated alkenes.

AbstractThe trisubstituted olefinic bond of sultam-imides 2 was hydrogenated in the presence of Pd/C with >90% diastereoface discrimination to give after saponification recovered auxiliary 7 and the β-substituted carboxylic acids 5 or6 in high e.e..

Asymmetric syntheses of α-amino acids from α-halogenated 10-sulfonamido-isobornyl esters.

AbstractTreatment of chiral α-haloesters 2 with NaN3 gave azidoesters 3 which on successive transesterification and hydrogenolysis furnished α-amino acids 5 and 9 in high e.e.

Asymmetric induction at C(β) and C(α) of N-enoyl sultams by 1,4-hydride addition/enolate trapping☆

AbstractConjugate addition of L-Selectride to α, β-enoyl sultams 1 and 4 followed by electrophilic trapping of the resulting enolates gave in one operation saturated imides with high β- and/or α- stereodifferentiation.

Optically pure, crystalline ‘acetate’-aldols from N-acetylbornane-10,2-sultam

AbstractO-Silylation of N-acetylsultam 2 gives O-silyl-N,O-ketene acetal 3 which undergoes TiCl4 promoted addition to aromatic and aliphatic aldehydes to afford, after flash chromatography, diastereomerically pure, crystalline aldols 5 which are readily converted to enantiomerically pure β-hydroxy carboxylic acids or esters.

Enantioselective addition of (Z)- and (E)-alkenylzinc bromides to aldehydes: asymmetric synthesis of sec-allylalcohols

AbstractIn situ prepared (Z)- and (E)-1-alkenylzinc bromides 5 were added to various aldehydes 1 in the presence of lithiated (+)-N-methylephedrine or (+)-2-(N,N-dimethylamino)-1,2-diphenylethanol to give sec. allyalcohols 7 in high optical purity with simple recovery of the chiral aminol 6.

Asymmetric alkylation of N-acylsultams: A general route to enantiomerically pure, crystalline C(α,α)-disubstituted carboxylic acid derivatives

AbstractSuccessive treatment of acylsultams 2 with nBuLi or NHMDS and primary alkyl halides, followed by crystallization, gave pure C(α)-alkylation products 4 and, via their non-destructive cleavage, enantiomerically pure alcohols 5 or carboxylic acids 6.

Asymmetric michael addition of a chiral ester-dienolate: enantioselective synthesis of (−)-khusimone☆

AbstractA double π-face-selective aprotic Michael addition of the lithium dienolate derived from the chiral senecioate 2b to cyclopentenone coupled with recovery of the auxiliary 14 serves for the enantioselective synthesis of (−)-khusimone (12) (Schemes 1 and 4).

Enantioselective synthesis of the Prelog-Djerassi lactonic acid via group-selective aldolization/desymmetrization of a meso dialdehyde with a chiral N-propionylsultam

AbstractThe group-selective aldolization/desymmetrization of meso dialdehyde 5 with a borylenolate derived from N-propionylbornanesultament-2 yields very efficiently lactols 6 with simultaneous generation of four stereogenic centers. Oxidation (6 → 7) followed by saponification of the sultam moiety (7 → 4) provided the Prelog-Djerassi lactonic acid 4 in a three step sequence in 61–71% overall yield.

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