A Valuable Approach to Enantiopure Partially Saturated Pyrrolo- and Indolo[1,2-a]indoles by Intramolecular Nitrone Cycloadditions to the Cyclohexene Ring

Beccalli, Egle M.; Broggini, Gianluigi; Farina, Alessandra; Malpezzi, Luciana; Terraneo, Alberto; Zecchi, Gaetano

doi:10.1002/1099-0690(200207)2002:13<2080::aid-ejoc2080>3.0.co;2-3

Cited by 18 publications

(6 citation statements)

References 2 publications

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“…Similar reactions were described in the absence of solvent under microwave irradiation, which allowed for reducing the reaction time from 4–5 h to 10–12 min with the same high yield of the product .…”

Section: Introductionmentioning

confidence: 93%

Synthesis and Some Biological Properties of Pyrrolo[1,2‐a]indoles

Monakhova

Ryabova

Makarov

2015

Journal of Heterocyclic Chem

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Section: Introductionmentioning

confidence: 93%

Synthesis and Some Biological Properties of Pyrrolo[1,2‐a]indoles

Monakhova

Ryabova

Makarov

2015

Journal of Heterocyclic Chem

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“…In several of the substrates, the nitrogen is benzylic; thus we sought conditions that were mild enough such that these compounds would not be over-reduced. Use of 10% Pd/C with NH 4 O 2 CH, H 2 -Pd(OH) 2 in HCl-MeOH, 37 or SmI 2 conditions 38 gave incomplete conversions and/or inconsistent yields. How- ever, treatment of the isoxazolidines with LiAlH 4 in Et 2 O cleanly provided the target amine diols that were immediately protected to facilitate isolation.…”

Section: Resultsmentioning

confidence: 99%

Succinct Synthesis of β-Amino Acids via Chiral Isoxazolines

Fuller,

Chen,

Minter

et al. 2005

J. Am. Chem. Soc.

145

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beta-Amino acids are important synthetic targets due to their presence in a wide variety of natural products, pharmaceutical agents, and mimics of protein structural motifs. While beta-amino acids containing geminal substitution patterns have enormous potential for application in these contexts, synthetic challenges to the stereoselective preparation of this class of compound have thus far limited more complete studies. We present here a straightforward method employing chiral isoxazolines as key intermediates to access five different beta-amino acid structural types with excellent selectivity. Of particular note is the use of this approach to prepare highly substituted cis-beta-proline analogues. The ready access to these diversely substituted compounds is expected to facilitate future studies of the structure and function of this important class of molecules.

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“…For these substrates, however, the use of 10% Pd/C with NH 4 O 2 CH provided poor conversion to the desired amine diol, likely due to steric hindrance; complete consumption of starting material was achieved under more forcing conditions [Pd(OH) 2 , HCl-MeOH] but the target amine diol was isolated in low yields. 11 SmI 2 was also investigated as a reductant 12 with inconsistent results. Of the conditions examined, LiAlH 4 in diethyl ether produced the most consistent yields and in situ protection of the intermediate free amine provided the protected amino diols 12 and 13 (Table 2).…”

Section: Scheme 1 Retrosynthetic Analysis Of B-amino Acidsmentioning

confidence: 99%

Synthesis and Structural Characteristics of Geminally Disubstituted β-Amino Acids

Fuller¹,

Chen²,

Minter³

et al. 2004

Synlett

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The syntheses of seven new b-amino acids containing aryl, alkyl, and heteroaryl substituents are outlined. The synthetic strategy employs densely functionalized chiral isoxazolines as key intermediates, enabling the preparation of single stereoisomers of these challenging targets. Solid-state characterization of two of the sterically encumbered targets is also reported.Stereoisomerically pure b-amino acids (1) serve as important constituents of both natural and non-natural materials and, as a result, have been the focal point of much synthetic effort. 1,2 b-Peptides (oligomers of b-amino acids) often adopt stable secondary structures such as helices, beta turns and beta sheets and have successfully been used to mimic the structure and function of naturally occurring aamino acid oligomers. 1b,c,g An additional attractive feature of b-amino acids is their increased resistance to proteolysis relative to a-amino acids, increasing their utility in biological settings. 3 Both the propensity to adopt secondary structure and the proteolytic stability of b-peptides are dependent on the substitution patterns of the b-amino acid constituents. The selective synthesis of b-amino acids with specific substitution patterns thus continues to inspire the development of novel synthetic methods. 1-7 A class of b-amino acids that has proven particularly difficult to access as single stereoisomers are those highly substituted at the C3 position (e.g., b 3,3 -and b 2,3,3 -amino acids). 2c,4-7 This is especially true in cases where the substituents (R 2 and R 3 in Scheme 1) are either sterically similar 6 and/or are bulky in size. 7 Consequently, although b 3,3 -and b 2,3,3 -amino acids are predicted to impart interesting structural and thus functional properties to oligomers, they have remained largely unexplored. 2c In this report we describe the selective preparation of seven new b-amino acids of this class incorporating alkyl, aryl, and heteroaryl substituents, expanding the diversity of b-amino acids available for application and study. In addition, solid-state structures of two of these densely functionalized amino acids are provided, confirming the stereochemical assignments and revealing packing arrangements of infinite sheets or helices dictated by hydrogen bonding.Isoxazolines (3) provide an excellent starting point for the preparation of b-amino acids 7 as they are easily prepared as single isomers from the 1,3-dipolar cycloaddition of nitrile oxides and allylic alcohols (Scheme 1). 8 Addition of a nucleophile to the C=N moiety of 3 then provides isoxazolidines (2) that contain the substitution patterns and stereochemical relationships present in the b-amino acid target.

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A Valuable Approach to Enantiopure Partially Saturated Pyrrolo- and Indolo[1,2-a]indoles by Intramolecular Nitrone Cycloadditions to the Cyclohexene Ring

Cited by 18 publications

References 2 publications

Synthesis and Some Biological Properties of Pyrrolo[1,2‐a]indoles

Synthesis and Some Biological Properties of Pyrrolo[1,2‐a]indoles

Succinct Synthesis of β-Amino Acids via Chiral Isoxazolines

Synthesis and Structural Characteristics of Geminally Disubstituted β-Amino Acids

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