Table 1.

Phosphine-Mediated [3 + 3] Aziridine/Allene Annulation^a

entry	PR3	mol%	yield (%)b	dr (trans/cis)c
1	PBu3	20	0	N/A
2	PPh3	20	15	10:1
3	PPh3	50	37	9:1
4	PPh3	100	73	9:1
5	PPh3	200	61	9:1
6d	PPh3	100	63	9:1
7e	PPh3	100	48	9:1
8	EtPPh2	100	2	–
9	Et2PPh	100	0	N/A
10	P(NMe2)3	100	0	N/A
11	P(OEt)3	100	0	N/A

^aAll reactions were performed using 0. 1 mmol of 1a and 4.8 equiv of 2 in CH₂Cl₂ at rt for 72 h, unless otherwise specified.

^bIsolated yield after chromatographic purification.

^cDiastereoisomeric ratio determined through HPLC (internal standard: 2-bromopyridine).

^d1,2-Dichloroethane as solvent; other common organic solvents provided isolated product yields of less than 10%.

^e40 °C, 48 h.