Reductive coupling of aldehydes and ketones to glycols (pinacol coupling) is a standard reaction of organic synthesis, 1 and Mg metal2 or various low-valent complexes of Ti, 3 Zr, 4 V, 5 Nb, 5a, 6 Sn, 7 or Sm8 can be used for efficient synthesis of inter-or intramolecular pinacol coupling, often with high diastereoselectivity. However, most conventional reductivecoupling methods are incompatible with aqueous conditions or protic ...