Table 1.

Ni-Catalyzed Conjugate Addition Reactions of Alkenes.^[a]

entry	R1	R2	R3	Major product	Yield (%)[b]	E:Z (2)[b]
1	H	Me	H	2a	52	95:5
2		n-hexyl		2b	76 58[c] 64[d]	95:5 95:5[c] 95:5[d]
3		PhCH2		2c	83	8:92
4[e,f]				2d	97	7:93
5		Me	Ph	2e	90	95:5
6		n-Pr		2f	94 86[d]	90:10 90:10[d]
7		i-Pr		2g	78	13:87
8[g]		Ph		2h	70	n.d.
9[h]		Me	p-anisyl	2i	94	91:9
10		n-Bu	2-furyl	2j	95	75:25
11		Et	2-thienyl	2k	95	75:25
12[f]	n-hexyl	n-hexyl	H	2l	67[i]	95:5
13[f]	Ph	n-hexyl	H	3a	70	81:19
14[f]		Me	p-anisyl	3b	55	91:9

^[a]See Supporting Information and eq 1. Standard conditions (entries 1–11): To a solution of Ni(cod)₂ (0.075 mmol) and Bu₃P (0.15 mmol) in toluene (1.5 mL) at 23 °C under ethylene (1 atm) were added Et₃N (1.5 mmol) and the enal or enone (0.25 mmol). Triethylsilyl triflate (0.44 mmol) was added dropwise at 0 °C. The mixture was stirred 48 h at 45 °C and purified by chromatography (SiO₂). In some cases CyPPh₂ (entry 12) or tricyclopentylphosphine (entries 13–14) was used in place of Bu₃P.

^[b]Determined by ¹H NMR.

^[c]Ethylene pressure 2 atm.

^[d]Fourfold larger scale (1 mmol enal used).

^[e]Compound 1d added over 48 h.

^[f]Reaction time 72 h; a lower yield was obtained with 24 h reaction time.

^[g]A dihydropyran from hetero-Diels–Alder reaction of 2 equiv of 1h was isolated (13%).

^[h]Reaction time 24 h.

^[i]Combined yield of 2l and 2l′ (79:21; compound 2l′ is the result of addition to the 1-position of 1-octene). See text and Supporting Information.