Table 1.

Ligand Optimization for Phosphoramidite Au^I-catalyzed [2+2]-Cycloaddition of 1b.^a

entry	Cat.	yield (%)b	ee (%)c
1	(S,S,S)-5a	81	34(+)
2	(S,S,S)-5b	91	14(+)
3	(S,S,S)-5c	67	56(+)
4	(S,S,S)-6	34	60(+)
5	(S,S,S)-7	81	70(+)
6	(R,R,R)-8	77	64(–)
7	(R,R,R)-9a	86	90(+)d
8	(S,R,R)-9a	73	52(–)
9	(R,R,R)-9b	87	32(+)
10	(R,R,R)-9c	22	4(+)
11	(R)-9d	88	32(+)
12	(R,R,R)-10a	66	56(–)
13	(R,R,R)-10b	---	---

^aReaction conditions: Cat (5 mol%), AgBF₄ (5 mol%), dichloromethane, 25°C, 24h. Only one diastereoisomer was observed in all cases.

^bIsolated yields after silica gel flash column chromatography.

^cEnantiomeric excess determined by enantiodiscriminating HPLC (see Supporting Information).

^dThe enantioselectivity was increased to 99% ee after a simple crystallization.