Table 5.

Phosphine-Catalyzed Annulations of the Azomethine Imine 1a with Ethyl 2,3-Butadienoate (2o)^a

entry	PR3	time (h)	3aob yield (%)c	6b yield (%)c
1 d	–	48	0	0
2	PPh3	24	8	19
3	EtPPh2	24	27	5
4	MePPh2	24	53	2
5	Me2PPh	24	69	15
6	PBu3	24	45	36
7	PMe3	12	62	3
8	HMPT	24	15	22

^a1.2 equiv of allenoate was used.

^bThe structure of this compound was verified through single-crystal X-ray analysis.

^cIsolated yield.

^dWithout phosphine catalyst.