The reaction of dichlorocarbene with 4,4-diphenyl-1-(2,4,6-tri-t-butylphenyl)-1-phosphabutatriene gave 2-dichloromethylene-3-diphenylmethylene-1-(2,4,6-tri-t-butylphenyl)-1-phosphirane via 2,2-dichloro-3-(2,2-diphenylethenylidene)-1-(2,4,6-tri-t-butylphenyl)-1-phosphirane.