The Zwitterionic Imidazolium Salt: First Used for Synthesis of 4-Arylidene-2-phenyl-5(4H)-oxazolones under Solvent-Free Conditions

Table 3

Preparation of azlactones from different aldehydes.

Entry	R (aldehyde)	Reaction time (h)	Azlactones	Isolate yields (%)^a	Mp found (°C)	Mp lit. (°C)
1	4-N(CH3)2	5.5	4a	70	211–213	214 [25]
2	Heliotropin	5	4b	67	197–199	199 [30]
3	4-OCH3	5	4c	62	155-156	159 [25]
4	4-CH3	6	4d	40	143-144	144 [25]
5	H	4	4e	75	168-169	166 [25]
6	4-Cl	5.5	4f	82	196-197	196 [25]
7	2-F	4	4g	55	166-167	168 [31]
8	4-CF3	3	4h	85	173-174	174 [32]
9	4-NO2	3	4i	89	240-241	239 [25]
10	2-Furaldehyde	5	4j	35	170–172	169 [25]
11	Isobutyraldehyde	5	—	ND^b	—	—
12	3-Phenylpropionaldehyde	5	—	ND^b	—	—

aBased on aldehyde; isolated yields based on aldehyde; 5 mmol aldehyde, 5.5 mmol hippuric acid, 5 mmol% imidazolium salt (1), and 15 mmol acetic anhydride were used; the reaction was carried out at 60°C.
^bNo product was detected.