Halogen bonding has received a significant increase in attention in the past 20 years. An important part of this interest has centered on catalytic applications of halogen bonding. Halogen bond (XB) catalysis is still a developing field in organocatalysis, although XB catalysis has outgrown its proof of concept phase. The start of this year witnessed the publication of the first example of a purely XB-based enantioselective catalytic reaction. While the selectivity can be improved upon, there are already plenty of examples in which halogen bonds, among other interactions, play a crucial role in the outcome of highly enantioselective reactions. This paper will give an overview of the current state of the use of XBs in catalytic stereoselective processes.
An asymmetric Michael addition of malononitrile to vinyl phosphonates was accomplished by hydrogen bond-enhanced bifunctional halogen bond (XB) catalysis.
Straightforward cascade reactions for the synthesis of spiro-cyclopropaneoxindoles are described. The target compounds are obtained in high yields and in good enantio- and diastereoselectivities via hydrogen bonding or iminium catalysis.