18-59 The Wittig reaction is useful for placing double bonds in less stable positions. For example, the following transformation is easily accomplished using a Wittig reaction. (a) Show how you would use a Wittig reaction to do this. 写出利用 Wittig reaction 完成该反应所需试剂 Ph3P =CH2 (b) Show how you might do this without using a Wittig reaction, and explain why the Wittig reaction is a much better synthesis. 若不用 Wittig reaction ,你将怎样完成该反应,解释为什么 Wittig reaction 是更好的合成方法