Iridium‐Catalyzed 1,3‐Rearrangement of Allylic Alcohols

Abstract

The allylic alcohol structural motif is prevalent in many important molecules and valuable building blocks. The rearrangement reaction is one of the most important transformations, however there are only a few reports for the 1,3‐rearrangement of allylic alcohols. Herein, a 1,3‐rearrangement of allylic alcohols catalyzed by an Ir(III) dihydride complex is described. This reaction could provide the corresponding less accessible allylic alcohols regio‐ and stereoselectively from readily available E/Z mixtures of the substrates. Furthermore, a tandem alkene isomerization followed by 1,3‐rearrangement of homoallylic alcohols was also realized. In addition, this rearrangement reaction could be used to synthesize the natural product Navenone B. Mechanistic investigation indicated that the reaction pathway involved a π‐allyl‐Ir(V) intermediate and that the dihydride in the iridium catalyst acts as a hydrogen switch to modulate the valence of the iridium center.

Synthesis of Indenone-Fused Pyran Derivatives from Aryl Enaminones and Cyclopropenones through Unsymmetrical Relay C–H Bond Activation and Double C–C/C–O Bond Formation

“…Through protodemetalation, VI is transformed into allylic alcohol VII along with regeneration of the catalyst. In the next stage of this cascade process, VII undergoes a 1,3-rearrangement of the allylic alcohol moiety under the reaction conditions to give intermediate VIII …”

Iridium-Catalyzed 1,3-Rearrangement of Allylic Ethers

“…(3) Controlling the E / Z selectivity of the product, particularly for products containing trisubstituted alkenes, poses a challenge (Scheme b). Inspired by the strategy of our developed Ir­(III) dihydride-catalyzed 1,3-rearrangement of allylic alcohols, which involved a π-allyl-Ir­(V) intermediate (Scheme c) and driven by our research interests in the development of metal–hydride-catalyzed transformations, herein, we report the first example of Ir­(III) dihydride-catalyzed 1,3-rearrangement of readily available allylic ethers (Scheme d). The reaction exhibits a broad substrate scope and delivers the difficultly prepared allylic ethers bearing large steric hindrance in good yields and exclusive stereoselectivities.…”

“…On the basis of the control experiments and previously reported work, a proposed reaction pathway is provided (Scheme ). First, Crabtree’s catalyst is activated by H 2 to form the active Ir­(III) dihydride species A .…”

“…(3) Controlling the E/Z selectivity of the product, particularly for products containing trisubstituted alkenes, poses a challenge (Scheme 1b). Inspired by the strategy of our developed Ir(III) dihydride-catalyzed 1,3rearrangement of allylic alcohols, which involved a π-allyl-Ir(V) intermediate (Scheme 1c) 16 On the basis of our previous research work, 16 the commercially available Crabtree's catalyst and the easily available allylic ether 1a were chosen as the precatalyst and the model substrate, respectively, for the optimization of the 1,3-rearrangement of allylic ethers (Table 1). To avoid hydrogenation of the alkene moiety of the substrate, the following procedure was adopted: Crabtree's catalyst was activated under a hydrogen atmosphere for 10 min, then the hydrogen was removed, and the substrate was added.…”

“…On the basis of our previous research work, the commercially available Crabtree’s catalyst and the easily available allylic ether 1a were chosen as the precatalyst and the model substrate, respectively, for the optimization of the 1,3-rearrangement of allylic ethers (Table ). To avoid hydrogenation of the alkene moiety of the substrate, the following procedure was adopted: Crabtree’s catalyst was activated under a hydrogen atmosphere for 10 min, then the hydrogen was removed, and the substrate was added.…”