Table 1. Reactions of Acetamide with Propionaldehyde in the Presence of Triarylphosphonium Salts: Optimization Studies.

	phosphonium salts 1
entry	Nr	X	Ar	solvent	time (h)	temp. (°C)	yielda (%)
1	1a	BF4	Ph	CH3CN	48	r.t.	87
2	1a	BF4	Ph	CH3CN	1	50	84
3	1a	BF4	Ph	CHCl3	1	50	86
4	1a	BF4	Ph	THF	1	50	74
5	1a	BF4	Ph	–	1	50/70	50b/78c
6	1a	BF4	Ph	CH3CN	1	50	49d
7	1b	Br	Ph	CH3CN	1	50	70
8	1b	Br	Ph	–	1	70	57c
9	1c	BF4	m-C6H4Cl	CH3CN	1	50	70
10	1c	BF4	m-C6H4Cl	CHCl3	1	50	71
11	1c	BF4	m-C6H4Cl	–	1	70	tracesc

^aIsolated yields.

^bThe yield was estimated based on the ¹H NMR spectrum; Attempts to isolate the pure product 1a failed due to low conversion of substrates.

^cThe molar ratio of substrates equals 1.2(aldehyde):1:1.

^dTriphenylphosphine and HBF₄ (tetrafluoroboric acid diethyl ether complex) were used instead of triphenylphosphonium tetrafluoroborate.