Table 1.

Optimization studies.

Entry	1	[Ag]	T[°C]	Solvent	t[h]	Yield[a] [%]	d.r.[b]	e.r.[c]
1	1 c	Ag2O	−20	EtOAc	60	78	89:11	90:10
2	1 a	Ag2O	−20	EtOAc	60	93	95:5	94:6
3	1 b	Ag2O	−20	EtOAc	60	82	90:10	90:10[d]
4	1 a	Ag2CO3	−20	EtOAc	24	64	91:9	94:6
5	1 a	AgOAc	−20	EtOAc	48	55	88:12	91:9
6	1 a	Ag2O	−20	TBME	36	74	88:12	94:6
7	1 a	Ag2O	−20	CH2Cl2	36	63	79:12	85:15
8	1 a	Ag2O	−20	iPrOAc	36	79	89:11	93:7
9	1 a	Ag2O	−30	EtOAc	96	84	90:10	94:6
10	1 a	Ag2O	0	EtOAc	48	84	89:11	92:8
11	1 a	–	−20	EtOAc	120	0	–	–
12	–	Ag2O	−20	EtOAc	120	0	–	–

^[a]Combined yield of both diastereomers after flash column chromatography.

^[b]The diastereomeric ratio (d.r.) is given as the trans/cis ratio and was determined by ¹HNMR analysis of the crude reaction mixture.

^[c]The enantiomeric ratios (e.r.) were determined by HPLC analysis on a chiral stationary phase.

^[d]Enantiomeric (4S,5R)-4 a was obtained. M.S.=molecular sieves, TMBE=tert-butyl methyl ether.