Palladium‐Catalyzed Coupling of Propargylic Alcohols with Boronic Acids under Ambient Conditions

Abstract

Summary of main observation and conclusion A highly efficient palladium‐catalyzed direct coupling of propargylic alcohols with organoboronic acids to synthesize tri‐ and tetra‐substituted allenes has been developed under mild reaction conditions. Many useful functional groups are tolerated in this process with high to excellent yields. Preliminary biological studies showed that several tri‐ and tetra‐substituted allenes exhibited potent anti‐diabetic activities.

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.…”

“…A related strategy has been reported by Mao and co-workers using Pd catalysis. 18 When propargyl-1,4-diols were used as substrates, a divergent reactivity toward the allene or the tetrahydrofuran product was observed depending on the aryl boron source (Scheme 4b). 19 The reaction with anhydrous boronic ester provided the corresponding allenols following the typical arylation/β-OH elimination pathway.…”

“…This transformation was assumed to proceed through initial OH-directed carborhodation of the triple bond, leading to a transient alkenyl-rhodium species that undergoes subsequent syn- β - OH elimination. A related strategy has been reported by Mao and co-workers using Pd catalysis …”

Zinc Iodide Catalyzed Synthesis of Trisubstituted Allenes from Terminal Alkynes and Ketones

“…These include cyclization and cycloaddition reactions, 2c , 3k , 4 hydroarylations, 5 hydroaminations, 6 hydrocyanations, 7 hydroalcoxylations, 8 and hydroborations. 9 In particular, when allenes bear carbonyl, amide, carboxyl, amine, or hydroxyl groups, at certain positions with regard to the allenic moiety, cyclization reactions toward heterocycles such as furans, nitrogen-containing cyclic compounds, or oxazoles take place, all having a wide range of synthetic utility. 1e , 6a , 10 …”