Design and Synthesis of Novel Isoxazole Tethered Quinone-Amino Acid Hybrids

Table 2

The yields of the compound 19b using various 1,3-cycloaddition reaction conditions.

Entry	Reaction conditions	Time	Yield (%)^a
1	NCS, NaHCO3, EtOAc	16 h	43
2	(Bu3Sn)2O, t-BuOCl, DCM [36]	16 h	11
3	NaOCl, Et3N, DCM	16 h	26
4	NCS, K2CO3, EtOAc, H2O	16 h	49
5	CuSO4·5H2O, L-Ascorbate, NaHCO3, t-BuOH, H2O [37]	12 h	30
6	NaI, 2,6-Lutidine, t-BuOCl, dioxane [38]	12 h	30
7	HTIB, CH3CN [39]	12 h	0
8	NBS, Et3N, DMF [40]	18 h	11
9	CrO2, CH3CN [41]	12 h	18

Determined by analysis of the crude reaction mixture by analytical LC/MS.
HTIB: hydroxy(tosyloxy)iodobenzene; NCS: N-chloro succinamide; NBS: N-bromosuccinamide.