Highly Enantioselective Radical Cation [2 + 2] and [4 + 2] Cycloadditions by Chiral Iron(III) Photoredox Catalysis.

Radical cations show a unique reactivity that is fundamentally different from that of conventional cations and have thus attracted considerable attention as alternative cationic intermediates for novel types of organic reactions. However, asymmetric catalysis to promote enantioselective radical cation reactions remains a major challenge in contemporary organic synthesis. Here, we report that the judicious design of an ion pair consisting of a radical cation and a chiral counteranion induces an excellent level of enantioselectivity. This strategy was applied to enantio-, diastereo-, and regioselective [2 + 2] cycloadditions, as well as enantio-, diastereo-, and regioselective [4 + 2] cycloadditions, by using chiral iron(III) photoredox catalysis. We anticipate that this strategy has the potential to expand the use of several mature chiral anions to develop numerous unprecedented enantioselective radical cation reactions.

A syn-Selective Aza-Aldol Reaction of Boron Aza-Enolates Generated from N-Sulfonyl-1,2,3-Triazoles and 9-BBN-H.

A syn-selective aza-aldol reaction of boron aza-enolates, generated from N-sulfonyl-1,2,3-triazoles and 9-BBN-H, is reported. It provides a sequential one-pot procedure for the stereoselective construction of 1,3-amino alcohols, having contiguous stereocenters, starting from terminal alkynes.