Oxazoline

Oxazolines ( dihydrooxazoles ) are heterocyclic compounds with five-membered ring contains one oxygen atom and one nitrogen atom and a double bond in the ring. The heteroatoms being oxygen and nitrogen are in the 1,3 -position to each other, wherein the oxygen atom in position 1 and the nitrogen atom is allocated to the 3 position. Depending on the position of the double bond in the heterocyclic ring, there are a plurality of mutually isomeric oxazolines:

• 2- oxazolines ( alternative name: 4,5- dihydrooxazoles, CAS: 504-77-8 ) containing a C = N double bond between the carbon atom 2 and the nitrogen atom
• 3- oxazolines ( alternative name: 2,5 - dihydrooxazoles, CAS: 95879-85-9 ) containing a C = N double bond between the carbon atom 4 and the nitrogen atom
• 4- oxazolines ( alternative name: 2,3- dihydrooxazoles ) contain a C = C double bond between carbon atoms 4 and 5

By far the most important are the 2- oxazolines. There are usually colorless, pyridinähnlich smelling liquids of weakly basic character whose lower limbs dissolve in water.

Synthesis

2- oxazolines are formed in dehydration of N-( 2-hydroxyalkyl ) amides by intramolecular cyclization. One can represent 2- oxazolines also from β - Halogenalkylamiden by heating with aqueous or alcoholic alkali. They can also be obtained by the condensation reaction of 1,2- amino alcohols with carboxylic acid esters, carboxylic acid amides or nitriles. The selective synthesis of 3- oxazolines is analogous to a variant of Asinger reaction of 2- haloaldehydes, ammonia, caustic soda and a oxo component (usually a ketone ). In some syntheses fall 3- oxazolines as by-products.

Reactivity

2- oxazolines are similar to the imido esters (synonym: imidate ester ) and can with strong reducing agents, such as with sodium and alcohol, are split by ring cleavage to N-substituted amino alcohols. With methyl p-toluenesulfonate as an initiator to 2-alkyl- substituted 2- oxazolines can be polymerized. It produces a linear polyethyleneimine After saponification. 3- oxazolines react as imines ( Schiff bases). 4- oxazolines are at the same time to connect the class of enamines.

2- oxazoline -5-ones react with carbonyl compounds under elimination of water to azlactones.