Dimethyl 2-(2-methoxy-4,4,5,5-tetramethyl-1,3,2lambda5-dioxaphospholan-2-ylidene)-3-phenyliminobutanedioate 生成 9-Methoxy-2,2,3,3-tetramethyl-6-phenyl-1,4-dioxa-6-aza-5λ5-phospha-spiro[4.5]deca-5(10),7-diene-7,8,9,10-tetracarboxylic acid tetramethyl ester