Table 1. Optimization of Iron-Catalyzed 1,3-Diene Synthesis from α-Allenyl Derivatives^a.

entry	R	[Fe]	solvent	3aa (%)	E/Z
1	Ac	Fe(acac)3	Et2O	93(92)b	7.5:1(5.0:1)c
2	Ac	FeCl3	Et2O	85	7.5:1
3	Ac	FeCl2	Et2O	16	4.3:1
4	Ac	Fe(acac)3	toluene	94	3.9:1
5	Ac	Fe(acac)3	THF	90	2.2:1
6	Me	Fe(acac)3	Et2O	36	17:1
7	Piv	Fe(acac)3	Et2O	85	4.7:1
8d	Ac	Fe(acac)3	Et2O	92	7.5:1
9e	Ac	Fe(acac)3	Et2O	96	3.5:1
10f	Ac	–	Et2O	<5	–
11g	Ac	–	Et2O	<5	–

^aReaction conditions: 1a (0.2 mmol), 2a (0.25 mmol), Fe catalyst (5.0 mol %), solvent (1.0 mL), −20 °C, 20 min. Yields and E/Z ratios were determined by ¹H NMR analysis of crude mixture with CH₂Br₂ as internal standards.

^bIsolated yield in parentheses.

^cE/Z ratio after isolation via chromatography in parentheses.

^d0 °C.

^e10 mol % of tetramethylethylenediamine (TMEDA) was added.

^fNo iron catalyst was added.

^gRun with Pd(OAc)₂ or CuI that would correspond to 0.1 wt % of the Fe(acac)₃ (5 mol %) used.