Table 1.

Evaluation of mupirocin methyl ester (14) cyclization leading to 15 and 16 with achiral catalysts and promoters.

Entry	Catalyst/conditions	Solvent	Time	Conversion [%]	15/16[b]
1[a]	LiCl	CH2Cl2	12 h	< 5	-
2[a]	ZnCl2	CH2Cl2	12 h	82	48:52
3[c]	Sc(OTf)3	CH2Cl2	12 h	77	57:43
4[d]	-	H2O	4 d	24	71:29
5	KH2PO4 buffer (pH 7)	H2O	4 d	> 98	48:52
6[e]	Cs2CO3	CH3OH	4 d	-	-
7[f]	LiHMDS	THF	4 d	-	-
8[g]	(p-NO2-C6H4O)2PO2H	CH2Cl2	5 d	> 98	70:30

^[a]Conditions: 14 (0.02 mmol), catalyst (20 mol%), CH₂Cl₂ (0.01 m).

^[b]Determined by RP HPLC.

^[c]Conditions: catalyst (20 mol%), CH₂Cl₂ (0.2 m).

^[d]70°C.

^[e]Cs₂CO₃ (10 equiv), CH₂Cl₂ (0.02 m).

^[f]LiHMDS (3equiv), CH₂Cl₂ (0.01 m).

^[g]Catalyst (20 mol%), CH₂Cl₂ (0.2 m).