Table 1.

Condition evaluation of the reaction^a

Entry	Variation from “standard condition”	Yield of 3a (dr)b
1	None	88% (3.7:1)
2	(NH4)2CO3 instead of NH4OAc	41% (1:1.1)
3	NH4HCO3 instead of NH4OAc	41% (1:1.1)
4	NH2CO2NH4 instead of NH4OAc	39% (1:1.2)
5	NH4Cl instead of NH4OAc	trace
6	NH4BF4 instead of NH4OAc	trace
7	Catalyst A instead of Catalyst C	61% (2.1:1)
8	Catalyst B instead of Catalyst C	54% (3.6:1)
9	w/o LiBF4	80% (2.6:1)
10c	Sc(OTf)3 instead of LiBF4	56% (3.3:1)
11c	Zn(OTf)2 instead of LiBF4	73% (3.7:1)
12	2,6-tBu2pyridine instead of LiBF4	88% (2.7:1)
13	2,6-lutidine instead of LiBF4	82% (2.5:1)
14	collidine instead of LiBF4	69% (2.9:1)
15	w/o PC, w/o light	N.D.

^aThe reaction was conducted using 1a (0.1 mmol), 2a (0.2 mmol) under indicated conditions.

^bYield and diastereomeric ratio (dr) were determined by ¹H NMR of crude mixture of the reaction using PhTMS as internal standard.

^cAdditive (20 mol%) was used.