Optimisation of reaction conditions for phosphaalkene dimerization to form diphosphetane 4a, followed by its collapse to alkene 5a.

	Dimerisation time	Conditions for conversion of 4a to 5a	Yield
1	3 h	LiOEt in THF	47%
2	24 h	LiOEt in THF	85%
3	3 days	LiOEt in THF	64%
4	24 h	THF	≤5%