What is Oxazole?

Oxazole is a unsaturated five-membered nitrogen, oxygen containing heteroaromatic with a pyridine like nitrogen and an oxygen atom present at 1,3-positions of the ring. Oxazoles are weakly basic, similar to imidazoles and can exist in partially reduced (2,5-dihydrooxazole or 4,5-dihydrooxazole) and completely reduced (oxazolidine) forms.

Physical Properties

The parent oxazole is a colorless liquid with a pyridine-like odor. It has a bp of 69–70°C.

Chemical Reactivity

Oxazole is a five-membered, nitrogen-oxygen heteroaromatic separated by methine (-CH) with a delocalized 6π electron ring system. However, complete delocalization of π electrons is restricted due to the presence of an electronegative oxygen atom (see the following diagram). The oxazole is considered to be a hybrid heteroaromatic system since its nitrogen atom behaves as a pyridine type and its oxygen atom behaves as a furan type.

Synthesis 

Due to the numerous applications of oxazole-based compounds in diverse fields, many exciting advances in the synthesis of these molecules have been reported. In the past, considerable attention has been made to develop high yielding protocols for the construction of oxazoles involving simple substrates. Generally, this scaffold has been constructed by using intramolecular condensation reactions in the presence of dehydrating agents. Apart from these, many eco-friendly and one-pot methodologies are also available to prepare these pharmaceutically important molecules.

From Primary Amides (a) The parent oxazole ring system was constructed on the heating of formamide with ethyl-α-hydroxyketosuccinate followed by alkaline hydrolysis and decarboxylation.

Similarly, a variety of oxazole derivatives were synthesized by the reaction of primary amides with various substrates.