Oxazolines

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Oxazolines (dihydrooxazoles) are heterocyclic compounds whose five-membered ring contains one oxygen atom and one nitrogen atom as well as a double bond in the ring. The heteroatoms oxygen and nitrogen are in the 1,3-position to one another, the oxygen atom being assigned the 1 position and the nitrogen atom the 3 position. Depending on the position of the double bond in the heterocyclic ring, there are several isomeric oxazolines:

Isomers 2-oxazolines, 3-oxazolines and 4-oxazolines (from left to right)

synthesis

2-Oxazolines are formed during the dehydration of N - (2-hydroxyalkyl) amides by intra-molecular cyclization. 2-Oxazolines can also be prepared from β-haloalkylamides by heating with aqueous or alcoholic alkalis. They can also be obtained by the condensation reaction of 1,2-amino alcohols with carboxylic acid esters, carboxylic acid amides or nitriles. 2-Oxazolines substituted in the 2-position can be obtained by reacting benzaldehydes with ethanolamine using 1,3-diiodo-5,5-dimethylhydantoin (DIH) as the oxidizing agent. The targeted synthesis of the 3-oxazolines takes place analogously to a variant of the Asinger reaction from 2-haloaldehydes, ammonia, sodium hydroxide solution and an oxo component (usually a ketone). In some syntheses, 3-oxazolines are obtained as by-products.

The first oxazoline was synthesized in 1884.

properties

Unsubstituted oxazolines
Surname 2-oxazoline 3-oxazoline 4-oxazoline
other names 4,5-dihydrooxazole 2,5-dihydrooxazole 2,3-dihydrooxazole
Structural formula 2-Oxazoline.png 3-Oxazoline.png Oxazoline4.png
CAS number 504-77-8 95879-85-9 6569-13-7
PubChem 21865211
Molecular formula C 3 H 5 NO
Molar mass 71.08 g mol −1
Physical state liquid
Brief description colorless liquid
boiling point 98 ° C
density 1.075 g cm −3
  • 2-Oxazolines contain a C = N double bond between carbon atom 2 and the nitrogen atom
  • 3-Oxazolines contain a C = N double bond between carbon atom 3 and the nitrogen atom
  • 4-Oxazolines contain a C = C double bond between carbon atoms 4 and 5.

By far the most important are the 2-oxazolines. They are mostly colorless, pyridine- like smelling liquids of a weakly basic character, the lower parts of which dissolve in water .

Reactivity

2- Oxazolines are cyclic imidic acid esters (synonym: imido esters ) and can be treated with strong reducing agents , e.g. B. with sodium and alcohol, with ring cleavage to N -substituted amino alcohols are split. With methyl p -toluenesulfonate as initiator , 2-alkyl-substituted 2-oxazolines can be polymerized. After saponification , a linear polyethyleneimine is formed from it . 3-Oxazolines react like imines ( Schiff bases ). 4-Oxazolines also belong to the enamine class of compounds .

2-Oxazolin-5-ones react with carbonyl compounds with elimination of water to form azlactones .

Metalation of the 2-alkyl substituent in 2-oxazolines enables a large number of chiral and achiral carboxylic acid derivatives to be produced from acids with one carbon atom poorer. Other reactions lead to aldehydes, ketones, lactones, amino acids, thiiranes and olefins. Because the oxazoline system is resistant to many reagents (RMgX, LiAlH 4 , CrO 3 , weak acids and bases), it can serve as a protective group for carboxylic acids in reactions in which these substances are involved.

See also

Individual evidence

  1. ^ Siegfried Hauptmann : Organic chemistry. 2nd Edition. German publishing house for basic industry, Leipzig 1985, ISBN 3-342-00280-8 , p. 577.
  2. ↑ S. Takahashi, H. Togo: An Efficient Oxidative Conversion of Aldehydes into 2-Substituted 2-Oxazolines Using 1,3-Diiodo-5,5-dimethylhydantoin. In: Synthesis . 2009, pp. 2329-2332, doi: 10.1055 / s-0029-1216843 .
  3. ↑ e-EROS Encyclopedia of Reagents for Organic Synthesis , 1999-2013, John Wiley and Sons, entry for 1,3-Diiodo-5,5-dimethylhydantoin, accessed December 19, 2017.
  4. ^ C. Ricco: 1,3-Diiodo-5,5-dimethylhydantoin. In: Synlett . 24, 2013, pp. 2173-2174, doi: 10.1055 / s-0033-1339477 .
  5. ↑ a b Maya Weber, Jürgen Jakob, Jürgen Martens : Synthesis and reactivity of 3-oxazolines. In: Liebig's annals of chemistry . 1992, pp. 1-6.
  6. ^ Julien Capra, Thierry Le Gall: Oxidative Conversion of Imines into Azadienes. In: Synlett. 2010, pp. 441-444.
  7. ↑ David C. Palmer: The Chemistry of Heterocyclic Compounds, Oxazoles Synthesis, Reactions, and Spectroscopy . John Wiley & Sons, 2004, ISBN 0-471-64930-9 , pp. 332 ( limited preview in Google Book search).
  8. ↑ a b c d Henry Wenker: Syntheses from Ethanolamine. V. Synthesis of Δ 2 -oxazolines and of 2,2'-Δ 2 -dioxazolines. In: Journal of the American Chemical Society. 60, 1938, p. 2152, doi: 10.1021 / ja01276a036 .
  9. ^ Siegfried Hauptmann: Organic chemistry. 2nd Edition. German publishing house for basic industry, Leipzig 1985, ISBN 3-342-00280-8 , p. 427.
  10. ^ Brockhaus ABC chemistry. FA Brockhaus Verlag, Leipzig 1965, p. 1003.
  11. ↑ Blandine Brissaul et al: Synthesis of Linear Polyethyleneimine Derivatives for DNA Transfection. In: Bioconjugate Chem . 14, 2003, pp. 581-587.
  12. ↑ AI Meyers, ED Mihelich: The utility of the 2-oxazolines in the synthesis. In: Angewandte Chemie. 88, 1976, p. 321, doi: 10.1002 / ange.19760881004 .