Copper-Catalyzed Reductive Ireland-Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates

Diastereo- and Enantioselective Construction of Stereochemical Arrays Exploiting Non-Classical Hydrogen Bonding in Enolborates

We report a copper-catalyzed reductive aldol addition to aldehydes and ketones, with pinacolborane as stoichiometric reductant, that results in the generation of stereodefined syn-aldol products. Cyclic, acyclic, fused and spirocyclic aldols bearing contiguous stereocenters are obtained with excellent yields and diastereoselectivities. Moreover, enantioselective reactions could be carried out with cycloalkenones to deliver aldols bearing three contiguous stereocenters and with up to 98 % ee. Computations reveal that the enolborate intermediate undergoes the syn-aldol reaction via a twist-boat transition state that is stabilized by non-classical hydrogen bonding interactions.

Recent Advances in Catalytic [3,3]-Sigmatropic Rearrangements

Carbon–carbon bond formation by [3,3]-sigmatropic rearrangement is a fundamental and powerful method that has been used to build organic molecules for a long time. Initially, Claisen and Cope rearrangements proceeded at high temperatures with limited scopes. By introducing catalytic systems, highly functionalized substrates have become accessible for forming complex structures under mild conditions, and asymmetric synthesis can be achieved by using chiral catalytic systems. This review describes recent breakthroughs in catalytic [3,3]-sigmatropic rearrangements since 2016. Detailed reaction mechanisms are discussed to enable an understanding of the reactivity and selectivity of the reactions. Finally, this review is inspires the development of new cascade reaction pathways employing catalytic [3,3]-sigmatropic rearrangement as related methodologies for the synthesis of complex functional molecules.