Robinson-Gabriel synthesis
The Robinson-Gabriel synthesis is a name reaction from the field of organic chemistry and was observed in 1907 by Siegmund Gabriel (1851-1924) and in 1909 by Robert Robinson (1886-1975). An intramolecular condensation and dehydrogenation of N- acyl- α- amino ketones to oxazoles takes place.
Overview reaction
The Robinson-Gabriel synthesis is carried out under dehydrating reagents such as sulphurous acid or phosphorus pentachloride (PCl 5 ).
The atoms marked in gray leave the molecule during the reaction and a ring closure occurs at the point marked in green . The radicals R 1 , R 2 and R 3 represent organic radicals.
Possible mechanism
The following mechanism of the Ronbinson-Gabriel synthesis is explained in general for any radicals R 1 , R 2 and R 3 with subsequent work-up by sulfurous acid.
The carbonyl group of the keto group of N -acyl- α -aminoketone 1 is protonated in the first step and reacts to intermediate 2 . The amide oxygen atom in turn attacks the carbonyl group of the keto group and thus reacts to form a dihydrooxazolol 3 . Hydrooxazole 4 is formed through intermolecular condensation and the 2,4,5-substituted oxazole derivative 5 is formed through dehydration through the sulfurous acid .
application
The Robinson-Gabriel synthesis is used to produce 2,5-disubstituted or 2,4,5-trisubstituted oxazole derivatives, in particular 2,5-diaryloxazole derivatives.
literature
- Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Ney Jersey 2009, ISBN 978-0-471-70450-8 , pp. 2410-2413.
Individual evidence
- ^ A b Zerong Wang: Comprehensive Organic Name Reactions and Reagents. First Edition, John Wiley & Sons, Ney Jersey 2009, ISBN 978-0-471-70450-8 , pp. 2410 f.