Reactions at the Halogen Atom

The halo function of haloacetates, as a primary halide and activated by the neighboring carboxyl function, undergoes easy displacement by nucleophiles of many types. This propensity opens the way for a wide variety of chemistries, which are discussed in the following sections. 

Reaction conditions la. SOCI2, MeOH, b. (BocljO, EtjN 2. NBS, CCI4 h.v.r.t.  

P(OMe 3, CHjClj reflux 4. RCHO DBU or Me2NC(=NH)NMe2, CH2Cl2 reflux  

Reaction conditions 1. Ph2C=NH, EtZ-PrjN, molecular sieves 3 A, acetonitrile  

These compounds are indispensable building blocks for the preparation of labeled cyclopropane- and cyclopropenecarboxyhc acids, as illustrated by the following three examples. In the first case 2,5-dimethylhexa-2,4-diene reacted with ethyl diazo[2- C]acetate at 120-140 C in the presence of copper powder as a catalyst or at room temperature in the presence of rhodium(II)pivalate to provide a 1 1 cisitrans mixture of ethyl [2- C]chrysanthemates 145 in 30-70% yield. Treatment of this mixture 

---