Table 1 Optimization of Retro-Pallada-DA reaction^a

Entry	R	[Pd]	Additive	Solvent	Yield (%)
Entry	R	[Pd]	Additive	Solvent	2a	3a	4a
1	-Ts	Pd(PPh₃)₄	HBr	Tol	3	5	6
2	-Ac	Pd(PPh₃)₄	HBr	Tol	16	19	20
3	-^tBu	Pd(PPh₃)₄	HBr	Tol	15	11	9
4	-Bz	Pd(PPh₃)₄	HBr	Tol	11	15	16
5	-Ac	PdBr₂	—	Tol/ⁱPrOH	23	12	8
6	-Ac	PdBr₂	PPh₃	Tol/ⁱPrOH	20	0	4
7	-Ac	PdBr₂	XantPhos	Tol/ⁱPrOH	18	5	3
8	-Ac	PdBr₂	CO	Tol/ⁱPrOH	35	9	2
9	-Ac	PdBr₂	CO	DCE/ⁱPrOH	61	0	0
10^b	-Ac	PdBr₂	CO	DCE/ⁱPrOH	<5	0	0
11	-Ac	PdBr₂	CO/O₂	DCE/ⁱPrOH	83	0	0
12^c	-Ac	PdBr₂	CO/O₂	DCE/ⁱPrOH	86(82)	0	0
13	-Ac	—	CO/O₂	DCE/ⁱPrOH	0	0	0

^a Optimization studies; reactions were performed with 0.2 mmol substrates (hydrazone or ketone) in 2.0 mL of solvent for 24 h; GC-FID yield was given. ^b The reaction was operated in a glovebox in the absence of oxygen. ^c 1-Phenylbut−3-en-1-one 1a and acetohydrazide were used as the substrates; isolated yield in parenthesis. Ts p-toluenesulfonyl, Ac acetyl, Bz benzoyl.

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