Copper‐Catalyzed Enantio‐, Diastereo‐, and Regioselective [2,3]‐Rearrangements of Iodonium Ylides

The first highly enantioselective, diastereoselective, and regioselective [2,3]‐rearrangement of iodonium ylides has been developed as a general solution to catalytic onium ylide rearrangements. In the presence of a chiral copper catalyst, substituted allylic iodides couple with α‐diazoesters to generate metal‐coordinated iodonium ylides, which undergo [2,3]‐rearrangements with high selectivities (up to >95:5 r.r., up to >95:5 d.r., and up to 97 % ee ). The enantioenriched iodoester products can be converted stereospecifically into a variety of onium ylide rearrangement products, as well as compounds that are not accessible by classical onium ylide rearrangements.     

Palladium‐Catalyzed C?H Activation of N‐Allyl Imines: Regioselective Allylic Alkylations to Deliver Substituted Aza‐1,3‐Dienes

A new mode of activation of an imine via a rare aza‐substituted π‐allyl complex is described. Palladium‐catalyzed C(sp³) H activation of the N‐allyl imine and the subsequent nucleophilic attack by the α‐alkyl cyanoester produced the 1‐aza‐1,3‐diene as the sole regioisomer. In contrast, nucleophilic attack by the α‐aryl cyanoester exclusively delivered the 2‐aza‐1,3‐diene, which was employed in an inverse‐electron‐demand Diels–Alder reaction for heterobiaryl synthesis.     

Palladium(II)‐Catalyzed Allylic C?H Oxidation of Hindered Substrates Featuring Tunable Selectivity Over Extent of Oxidation

The use of Oxone and a palladium(II) catalyst enables the efficient allylic C H oxidation of sterically hindered α‐quaternary lactams which are unreactive under known conditions for similar transformations. This simple, safe, and effective system for C H activation allows for unusual tunable selectivity between a two‐electron oxidation to the allylic acetates and a four‐electron oxidation to the corresponding enals, with the dominant product depending on the presence or absence of water. The versatile synthetic utility of both the allylic acetate and enal products accessible through this methodology is also demonstrated.     

Dehydrogenative Silylation of Alkenes for the Synthesis of Substituted Allylsilanes by Photoredox,Hydrogen‐Atom Transfer,and Cobalt Catalysis

A synergistic catalytic method combining photoredox catalysis, hydrogen‐atom transfer, and proton‐reduction catalysis for the dehydrogenative silylation of alkenes was developed. With this approach, a highly concise route to substituted allylsilanes has been achieved under very mild reaction conditions without using oxidants. This transformation features good to excellent yields, operational simplicity, and high atom economy. Based on control experiments, a possible reaction mechanism is proposed.