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  • 1
    Electronic Resource
    Electronic Resource
    An Unusual Rearrangement of a Lithiated N-Acyl-tetrahydroisoquinoline to an Amino-indan Skeleton and Structural Comparison of 3-Amino-2-methylindan- and -tetrahydronaphthalene-2-carboxylic Acids as Possible Building Blocks for Peptide-Turn Mimics (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2640-2653 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium 1-lithio-6,7-dimethoxy-3-methyl-2-pivaloyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylate rearranges to the dilithio derivative of 5,6-dimethoxy-2-methyl-1-(pivaloylamino)indan-2-carboxylic acid (2, [1,2]-sigmatropic shift with retention of configuration) by 1,2-migration resembling the Wittig rearrangement of deprotonated ethers (Scheme 2). The structure, including absolute configuration of the rearrangement product, was determined by X-ray diffraction. Structural conditions for the rearrangement to occur are tested by subjecting various other tetrahydroisoquinoline derivatives (6, 7, 10, 15) to the metalating conditions. Only one other compound was found to undergo the same rearrangement (15 → 16). Possible mechanisms of the rearrangement are discussed (B-G). Due to the presence of a tetrasubstituted C-atom, the indan-type β-amino-acid derivative 2 has a conformationally locked structure (N—C—C—CO2R dihedral angle 44°). For comparison, the corresponding tetralin-type β-aminoacid derivatives 19-22 were prepared, and it was shown by X-ray analysis (of the ester 21) that these have larger dihedral angles (ca. 60°). It is proposed that β-amino acids of the type described here could be incorporated into peptides, providing bents of known angles along the peptide backbone.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760721
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  • 2
    Electronic Resource
    Electronic Resource
    Scope and limitations of the TiCl4-mediated additions of isocyanides to aldehydes and ketones with formation of α-hydroxycarboxylic acid amides (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 507-517 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Anwendungsbreite der TiCl4-induzierten Addition von Isocyaniden an Aldehyde und Ketone unter Bildung von α-HydroxycarbonsäureamidenDie Umsetzung der aus achiralen (8-12) oder chiralen (13-22) Isocyaniden und TiCl4 gebildeten Addukte mit aliphatischen oder aromatischen Aldehyden oder mit Ketonen (Aceton, Cyclohexanon, Acetophenon) liefert nach wäßriger Aufarbeitung α-Hydroxyamide (27-55) in einer Passerini-artigen Reaktion. Dies ist mit Substraten durchführbar, Welche die verschiedensten funktionellen Gruppen enthalten: aromatische, auch methoxysubstituierte Ringe, Heterocyclen, Amino-, Ether-, Ester- und Amidgruppen, Halogen- und Phosphonatsubstituenten. Die Ausbeuten liegen zwischen 14 und über 95%, wobei die tieferen Werte bei höher funktionalisierten Isocyaniden auftreten. Mit den chiralen Isocyaniden wird keine Diastereoselektivität beobachtet. Bei Derivaten R—NC, deren R-Gruppe relativ stabile Kationen bildet (z. B. t-Alkyl-, Benzyl-), kommt es zu einer Cyanhydrine liefernden Konkurrenzreaktion (s. Schema 2).
    Notes: The adducts obtained from TiCl4 and achiral (8-12) or chiral, nonracemic (13-22) isocyanides are combined with aldehydes (aromatic or aliphatic) and ketones (acetone, cyclohexanone, acetophenone) to give, after aqueous workup, α-hydroxyamides (27-55) [Passerini-type reaction]. The transformation is compatible with a variety of functional groups (aromatic and heterocyclic rings, amino, ether, ester, and amido groups, halides, and phosphonate substituents). The yields range from 14 to over 95% (with the lower values in the case of more highly functionalised isocyanides). No diastereoselectivity is observed with chiral isocyanides. If the R groups of the isocyanide (R—NC) form a rather stable cation (t-alkyl or benzylic), cyanohydrins may result from the reaction, rather than the N-substituted α-hydroxyamides (see Scheme 2).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881210319
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  • 3
    Electronic Resource
    Electronic Resource
    Herstellung von α-verzweigten Phenylalaninen und von 1,1-disubstituierten Ethylendiaminen über chirale Imidazolidinone und Oxazolidinone aus Glycin - präparative und mechanistische Aspekte (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 785-799 
    Details
    ISSN: 0170-2041
    Keywords: Tetrahydroisoquinoline to indane rearrangement ; α-Amino acids, α-branched, enantiomerically pure ; Cyclic acetals of glycine ; 1,3-Imidazolidinones ; 1,3-Oxazolidinones ; 1,2-Ethylendiamines, geminally substituted, enantiomerically pure ; Mechanism of alkylation of heterocyclic enolates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of α-Branched Phenylalanines and of 1,1-Disubstituted Ethylenediamines via Chiral Imidazolidinones and Oxazolidinones of Glycine - Preparative and Mechanistic AspectsTo test the structural prerequisites for a new carbanionoid rearrangement of 3-methyl-2-pivaloyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid to N-(t-butoxycarbonyl)-1-amino-2-methylindan-2-carboxylic acid (A → B), various α-branched phenylalanines (C) were required. Geminal dialkylation of the chiral glycine building block Boc-BMI (1) occurs in excellent yields and selectivities and can be carried out in a one-pot procedure (products 2-10). However, phenylalanines with methoxy groups on the benzene ring and α-branching by substituents larger than methyl cannot be set free by hydrolysis of the corresponding imidazolidinones, which, on the other hand can be reduced through N-methyl amino acid amides (13-15) to geminally disubstituted N-methyl-ethylenediamines (16-18). A series of 2-t-butyl-5-oxo-1,3-oxazolidin-3-carboxylates (19-27) was prepared and could be resolved on ChiraSphere, Chiralcel OD, and Pirkle columns (Table 1). Alkylation (Me, Et, Bu), allylation, and benzylation of the rac-oxazolidinones lead to trans-disubstituted products (29-43) which were alkylated a second time (products 44-51); yields and selectivities are satisfactory (Table 2). Hydrolysis of 4,4-dibenzyl-substituted oxazolidinones to the amino acid derivatives is possible (examples 52-54). - Comparison of the methylation selectivities of seven 2-t-butyl-1,3-oxazolidin-5-one Li-enolates bearing different N-acyl groups (Figure 1) and an X-ray crystal structure analysis of a phenol carbamate (26, Figure 2 and Table 3) show that our previous mechanistic model obtains: t-butyl in the COR group gives the poorest selectivity (3:1), O-phenyl the highest (〉50:1). This is compatible with the view that the acylgroups (on pyramidalized nitrogens!) in these heterocyclic acetals occupy one face of the average plane of the rings, and the substituents on the acetal center (here t-Bu) the other one (Figure 1).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301124
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