Rh‐Catalyzed Reaction of Propargylic Alcohols with Aryl Boronic Acids–Switch from β‐OH Elimination to Protodemetalation

Abstract

Summary of main observation and conclusion It is known that Rh‐catalyzed reaction of propargylic alcohols with aryl metallic reagents undergoes SN2’‐type reaction affording allenes via a sequential arylmetalation and β‐OH elimination process. Here we report a Rh/Ag‐cocatalyzed reaction of propargylic alcohols with organoboronic acids affording stereo‐defined (E)‐3‐arylallylic alcohols via arylmetalation and protodemetalation with a high regio‐ and stereoselectivity under very mild conditions. The reaction exhibits a good substrate scope and the compatibility with synthetically useful functional groups with no racemization for optically active propargylic alcohols. Such a reaction may also be extended to homopropargylic alcohols with a remarkable regioselectivity and exclusive E‐stereoselectivity.

A Highly Efficient Dimeric Manganese‐Catalyzed Selective Hydroarylation of Internal Alkynes

“…Arylboronic acids are commercially abundant and easy to handle reagents, which recently have gained considerable momentum in selective hydroarylation of alkynes . For example, after much research with palladium, rhodium, copper, and nickel catalysts, it is recognized that the utilization of electronic and directing group strategy can normally control the regioselectivity of hydroarylation but the inherent high reactivity of these metals towards a wide range of useful functional groups simultaneously compromises their chemoselectivities (Scheme a). On the other hand, it requires several steps to install and remove the directing group before and after reactions.…”

Transition-Metal-Catalyzed Functionalization of Alkynes with Organoboron Reagents: New Trends, Mechanistic Insights, and Applications

“…A salient example of this ligand modulation has been recently reported by Dou and co-workers in the context of Rh-catalyzed synthesis of 1,1-disubstituted indenes from propargyl alcohols and arylboronic acids (Scheme ). This reaction is another important transformation involving the Rh-dyotropic rearrangement, in which the 1,4-shift is preferred over of the typically observed βOH elimination − or hydroarylation pathways, − as previously discussed in Section . The use of DPEPhos L 8 as a ligand was key for success which, in combination with [Rh­(OH)­(cod)] 2 , is able to promote a sequential aryl-rhodation of the CC triple bond, followed by 1,4-rhodium migration to a previously existing aryl group in the substrate.…”

“…Ma and co-workers 20 managed to prevent the β−OH elimination pathway in the Rh-catalyzed reaction of tertpropargylic alcohols with boronic acids, thereby attaining high selectivity toward the alkyne hydroarylation product (Scheme 5a). The reaction proceeds smoothly at room temperature cocatalyzed by the Rh III /Ag I system in the presence of NaOAc to provide the corresponding 3-arylallylic alcohol with a remarkable regioselectivity and exclusive E-stereocontrol.…”

Noncovalent Interaction- and Steric Effect-Controlled Regiodivergent Selectivity in Dimeric Manganese-Catalyzed Hydroarylation of Internal Alkynes: A Computational Study

“…Transition metal-catalyzed hydroarylation reactions of alkynes have emerged as a powerful protocol to produce arylethene derivatives, which are widely applied in the synthesis of natural products, biologically active molecules, and various drug molecules . In this regard, significant advances have been achieved by employing a broad range of catalysts including manganese, nickel, copper, palladium, rhodium complexes, etc . In this transformation, precise control of arylation sites on alkyne carbon is still one of the major challenges.…”