Preparation of Ethyl (R)‐3‐Hydroxy‐4‐chlorobutyrate (III) by Selective Reduction of (R)‐4‐(Trichloromethyl)‐oxetan‐2‐one (I): Key Intermediate to (R)‐Carnitine (IVa) and (R)‐4‐Amino‐3‐hydroxybutyric Acid (IVb).