Tunable reactivity of geminal bis(silyl) enol derivatives leading to selective exo-IEDDA or Sakurai allylation with a β,γ-unsaturated ketoester

Exo-Selective Diels-Alder Reactions

The Diels-Alder reaction stands as one of the most pivotal transformations in organic chemistry. Its efficiency, marked by the formation of two carbon-carbon bonds and up to four new stereocenters in a single step, underscores its versatility and indispensability in synthesizing natural products and pharmaceuticals. The most significant stereoselectivity feature is the "endo rule". While this rule underpins the predictability of the stereochemical outcomes, it also underscores the challenges in achieving the opposite diastereoselectivity, making the exo-Diels-Alder reactions often considered outliers. This review delves into recent examples of exo-Diels-Alder reactions, shedding light on the factors inverting the intrinsic tendency. We explore the roles of steric, electrostatic, and orbital interactions, as well as thermodynamic equilibriums in influencing exo/endo selectivity. Furthermore, we illustrate strategies to manipulate these factors, employing approaches such as bulky substituents, s-cis conformations, transient structural constraints, and innovative control physics. Through these analyses, our aim is to provide a comprehensive understanding of how to predict and design exo-Diels-Alder reactions, paving the way for new diastereoselective catalyst systems and expanding the chemical scope of Diels-Alder reactions.

3-Silyl-3-Borylhex-4-Enoate: A Chiral Reagent for Asymmetric Crotylboration of Aldehydes

A nonracemic 3-silyl-3-borylhex-4-enoate reagent has been developed. Its asymmetric crotylboration of aldehydes provides Z-anti-homoallylic alcohols possessing a trisubstituted vinylsilane in high yields with excellent stereo- and enantioselectivity. Diverse decoration of vinylsilane and ester groups, as well as formation of functionalized THF rings, showcase the potential of the approach in the synthesis of polyketide natural products.

Formal Carbene C-H Bond Insertion in the Cu(I)-Catalyzed Reaction of Bis(trimethylsilyl)diazomethane with Benzoxazoles and Oxazoles

A Cu(I)-catalyzed cross-coupling reaction of bis(trimethylsilyl)diazomethane and benzoxazoles/oxazoles is reported. A wide range of functional groups can be tolerated in this transformation. This reaction provides a new method to directly introduce a 1,1-bis(trimethylsilyl)methyl group into heteroaromatic C-H bonds. Subsequent transformations of 1,1-bis(trimethylsilyl)-methylated heteroaromatic compounds are also presented.