Table 1. Effect of Base for [3 + 2] Cycloaddition Reaction in CH₃OH Solvent^a.

entry	base	pKa	equiv	time	oxazoline yield (%)b3a	oxazole yield (%)b4a
1				12 h	0	0
2	triethylamine	10.75	2	6 h	95	0
3	N,N-diisopropylethylamine	10.74	2	6 h	95	0
4	imidazole	6.9	2	6 h	92	0
5	N-methymorpholine	7.4	2	6 h	93	0
6	NaHCO3	5.95	2	6 h	90	0
7	K2CO3	9.1	2	2 h	0	94
8	K3PO4	11.74	2	1.5 h	0	95

^aReaction was performed using 1a (1.18 mmol), 2a (1.18), and 2.36 mmol base.

^bYield of the isolated product.