Table 1.

Optimization of thiazolidine exchange reaction of 3a.

entry	Reaction conditionsa	time (h)	3a/3b ratiob	2 (%)c
1	pH 4, rt	24	45/55	3
2	pH 4, rt	48	44/56	2
3	pH 4, rt	72	46/54	10
4	pH 5, rt	24	71/29	5
5	pH 5, rt	48	68/32	10
6	pH 5, rt	72	52/48	9
7	pH 6, rt	24	96/4	0
8	pH 6, rt	48	97/3	0
9	pH 6, rt	72	90/10	0
10	pH 7, rt	72	98/2	0
11	pH 4, 35 °C	24	45/55	18d
12	pH 4, 35 °C	48	35/65	16e

^aThe starting concentration of each component was 1 mM; the reaction mixture was stirred in a buffered acetate solution at pH 4 and pH 5, and in a phosphate solution at pH 6 and pH 7.

^bThe ratio was determined by ¹H NMR.

^cThe mass balance was quantitative

^dTotal yield 3a + 3b (64%).

^eTotal yield 3a + 3b (49%).