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Volumn , Issue 8, 1996, Pages 1259-1276

Alkylations of chiral imidazolidinones derived from di- and triglycine and attempts at cyclisations to give cycloisodityrosines

Author keywords

Diglycine; Imidazolidin 4 ones, 2 tert butyl , from di and triglycines; Li enolates of peptides; Li enolates, alkylations imidazolidinone derivatives; Triglycine

Indexed keywords


EID: 0010369610     PISSN: 09473440     EISSN: None     Source Type: Journal    
DOI: 10.1002/jlac.199619960805     Document Type: Article
Times cited : (2)

References (55)
  • 1
    • 33748973610 scopus 로고
    • Part of the Dissertation (ETH No 11350) of Eidgenössische Technische Hochschule Zürich
    • Part of the Dissertation (ETH No 11350) of O.B., Eidgenössische Technische Hochschule Zürich, 1995.
    • (1995)
    • B., O.1
  • 11
    • 0003598101 scopus 로고
    • (Eds.: B. Ernst, C. Leumann), Verlag Helvetica Chimica Acta (Basel) and VCH (Weinheim)
    • D. Seebach, A. K. Beck, A. Studer in Modern Synthetic Methods (Eds.: B. Ernst, C. Leumann), Verlag Helvetica Chimica Acta (Basel) and VCH (Weinheim), 1995.
    • (1995) Modern Synthetic Methods
    • Seebach, D.1    Beck, A.K.2    Studer, A.3
  • 21
    • 33748958868 scopus 로고    scopus 로고
    • note
    • We also synthesised the triglycine derivative with an imidazolidinone unit in the middle, see Scheme 1. However, this compound could be alkylated regioselectively only at its ester position, and we were unable to deprotect it by opening the imidazolidinone ring; consequently, we did not study it further.
  • 24
    • 33748963445 scopus 로고    scopus 로고
    • note
    • The electrophiles 10 and 16 were so reactive that they were slowly hydrolysed when in contact with silica gel under solvent-free conditions.
  • 27
    • 33748962208 scopus 로고    scopus 로고
    • note
    • We were not able to improve the reactivity by using three equiv. of LiHMDS as base or by trying to prepare the endo-cyclic monoenolate from the corresponding free acid 3 and two equiv. LDA.
  • 28
    • 33748986720 scopus 로고    scopus 로고
    • note
    • This problem became unsolvable with propionaldehyde, where reaction products could not be separated at all from the starting material.
  • 29
    • 33748980432 scopus 로고    scopus 로고
    • note
    • The reasons for these poor and not always reproducible yields are not clear. Especially in the case of alkylations via the dienolate there were substantial amounts of side products.
  • 30
    • 33748952135 scopus 로고    scopus 로고
    • note
    • [3e], the lower yields obtained here were rather unexpected. Since similar experiments with the corresponding Moc-protected imidazolidinone led to still lower yields (<15%), it seems to us that the aromatic ring of the Z-protecting group must play an important role in the alkylation of the enolates of these diglycine derivatives.
  • 31
    • 85086528260 scopus 로고    scopus 로고
    • note
    • 4) nor by adding DMPU or LiBr.
  • 35
    • 33748973956 scopus 로고    scopus 로고
    • note
    • Attempts to alkylate the corresponding ester 4 at its endo-cyclic position led to a mixture of products alkylated in both endo-and exo-cyclic positions.
  • 36
    • 85086526874 scopus 로고    scopus 로고
    • note
    • [3].
  • 37
    • 85086526584 scopus 로고    scopus 로고
    • note
    • [5].
  • 40
    • 33748973791 scopus 로고    scopus 로고
    • note
    • This effect was also observed in experiments aimed towards deprotection of 21 and 27.
  • 47
    • 33748968502 scopus 로고    scopus 로고
    • note
    • The reaction of methyl iodide with 1 was slower than those of the bromides 10, 12, and 16.
  • 53
    • 33748974633 scopus 로고    scopus 로고
    • note
    • It is well known that benzylic halides couple to 1,2-diphenyl-ethane derivatives upon treatment with alkyllithium.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.