Table 1.

Preliminary study of the reactions between allenoate 1 and aldehydes 2^a

Entry	Ar	R	Solvent	Time [h]	Temp [°C]	Yieldb [%]
1	C6H5	C6H5	Benzene	24	Reflux	28 (3a)
2	C6H5	C6H5	Toluene	24	Reflux	28 (3a)
3	C6H5	C6H5	EtOAc	24	Reflux	28 (3a)
4c	C6H5	C6H5	Neat	2	160	25 (3a)
5	4-CF3C6H4	C6H5	Benzene	24	Reflux	33 (3b)
6	4-NCC6H4	C6H5	Toluene	24	Reflux	33 (3c)
7	4-NCC6H4	C6H5	Toluene	24	rt	Trace (3c)
8	4-NCC6H4	C6H5	MeOH	24	rt	0
9	4-BrC6H4	C6H5	Benzene	24	Reflux	21 (3d)
10	3-HOC6H4	C6H5	Benzene	24	Reflux	0
11c,d	4-Me2NC6H4	C6H5	Toluene	54	160	0
12c	4-Me2NC6H4	C6H5	Neat	48	160	0
13	4-NCC6H4	4-MeC6H4	Toluene	24	Reflux	21 (3e)
14e	4-NCC6H4	C6H5	Toluene	24	Reflux	37 (4a)

^aAllenic ester (1.2 mmol) in solvent (10 mL) was added slowly (over 2 h) via a syringe pump into the mixture of the other reaction components (1.0 mmol of aldehyde and 1.0 mmol of phosphine) in solvent (5 mL).

^bIsolated yield of product.

^cReaction was performed in a sealed tube.

^dTotal volume of solvent: 2 mL.

^eBF₃·Et₂O (10 mol %) was added to the reaction mixture.