Showing papers by "Wolfgang Oppolzer published in 1986"
TL;DR: In this article, the loganin precursor was transformed into norbornanone 20, which upon Baeyer-Villiger oxidation led to the suitably substituted cyclo- pentane 22 from which 1-B-O-methyl lignin aglucone was rea- fily available.
118 citations
TL;DR: EtAlCl2-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation as mentioned in this paper.
Abstract: EtAlCl2-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived ‘anti’ -aldols (via silyl-directed α-methylation).
79 citations
TL;DR: Succesive treatment of chiral esters with LiN(i-Pr)2/Me3SiCl and di(tert-butyl) azodicarboxylate/TiCl4/Ti(i)-PrO)4 gave N,N′ -di[ (tertbutoxy)carbonyl]hydrazino esters 9 which on deacylation, hydrogenolysis, transesterification, and acidic hydrolysis furnished (2S)-α-amino acids 6 in high enantiomeric purity with efficient
Abstract: Succesive treatment of chiral esters 1 with LiN(i-Pr)2/Me3SiCl and di(tert-butyl) azodicarboxylate/TiCl4/Ti(i-PrO)4 gave N,N′ -di[(tert-butoxy)carbonyl]hydrazino esters 9 which on deacylation, hydrogenolysis, transesterification, and acidic hydrolysis furnished (2S)-α-amino acids 6 in high enantiomeric purity with efficient recovery of the auxiliary alcohol 7.
70 citations
TL;DR: In this article, the treatment of chiral α-haloesters with NaN3 gave azidoesters 3 which on successive transesterification and hydrogenolysis furnished α-amino acids 5 and 9 in high e.g.
65 citations
TL;DR: Conjugate 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 as discussed by the authors.
56 citations
TL;DR: In this paper, the TiCl4-mediated addition of silyketene acetals 2 and 7 to aldehydes gave aldols 4 and 9, respectively, with high π-face and "anti" differentiation.
Abstract: Starting from acetates 1 and propionates 6, TiCl4-mediated addition of their silyketene acetals 2 and 7 to aldehydes gave aldols 4 and 9, respectively, with high π-face and ‘anti’ differentiation (Schemes, and Tables 1 and 2). Alternation of the (E/Z)-enolate geometry led to reversed α- and β-inductions (7 → 9b, 8 → 10b). Non-destructive removal of the auxiliary yielded enantiomerically pure β -hydroxycarboxylic acids 13.
53 citations
TL;DR: The deoxypolyproplonate 13 was synthesized from (S)-2-methyl-1-butanol by a reaction sequence featuring two highly π-face selective organocopper/enoate additions 1 → 4 and 7 → 8.
52 citations
TL;DR: Starting from (S)-3-methyl-1-penten-5-o1 3a enantiomerically pure (+)-α-skytanthine 9, (+)-δ-skyTanthine 11 and (+)-iridomyrmecin 12 were synthesized via the magnesium-ene reaction.
48 citations
TL;DR: The 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 β-substitized carboxylic acids 5 or 6 in high e.g.
47 citations
TL;DR: In this paper, an asymmetric conjugate addtion/Mannich reaction tandem (10→12) and a type-II-magnesiumene cyclization/oxidation sequence (14→1 + 16) were synthesized starting from aldehyde 5.
Abstract: Enantiomerically pure β-necrodol (1) and its 1-epimer 16 have been synthesized starting from aldehyde 5. The two key steps are an asymmetric conjugate addtion/Mannich reaction tandem (10→12) and a type-II-magnesiumene cyclization/oxidation sequence (14→1 + 16).
46 citations
TL;DR: In this paper, P-stabilized 1-alkenylcopper reagents undergo efficient 1,4-additions to enoates 1 and 5, and obtain acids 3, 7 or alcohols 4, 8 with recovery of the auxiliary.
TL;DR: The sesquiterpene (±)chokol-A was synthesized in a diastereoselective manner starting from 1-hexen-5-one-trisylhydrazone as mentioned in this paper.
TL;DR: The sesquiterpene (±)-6-protoilludene and its C(3)-epimer 11 were synthesized from aldehyde 5. The key steps are a regio- and stereo-selective type-I-magnesium-ene reaction 4 → 3 and an intramolecular vinylketene/alkene addition 2 → 9a + 9b.
TL;DR: In this article, a cycloaddition of cyclopentadiene to allenic ester with 95 % endo-and 99.2% πpH-face selectivities was proposed.
Abstract: Starting from (+)- or (−)-camphor, the antipodal alcohols 14 and 18, respectively, have been prepared; the corresponding acrylates 15 and 19 underwent TiCl2(i-PrO)2-mediated Diels-Alder additions to cyclopentadiene to give adducts 20a and 22a respectively, with 95 % endo- and 99.2% πpH-face selectivities. Adduct 22a was converted to enantiomerically pure norbornenone 26. Addition of 1,3-butadiene to acrylate 15 in the presence of TiCl4 afforded 3-cyclohexenyl carboxylate 29 with > 95.6 % stereodifferentiation. The TiCl2(i-PrO)2-promoted [4 + 2] cycloaddition of cyclopentadiene to allenic ester 43 proceeding with 99 % face differentiation served as the key step for an efficient enantioselective synthesis of (−)-β-santalene ((−)-41) with concomitant recovery of the chiral control alcohol 14.