Nickel/Brønsted acid dual-catalyzed regioselective C–H bond allylation of phenols with 1,3-dienes

Abstract

Selective alkylation of phenols is an efficient strategy for the preparation of phenol derivatives. However, owing to the ambident nucleophilic reactivity of these substrates, chemo-selectivity is the predominant challenge in...

Palladium-Catalyzed Chemo- and Regioselective C–H Bond Functionalization of Phenols with 1,3-Dienes

“…In addition, we briefly studied the effect of additives. Unexpectedly, the reaction was thwarted in the presence of 10 mol % TsOH, which is in sharp contrast to the results reported in literature with Ni catalysis ( eq 5 ) …”

“…On the basis of the above facts and previous literature, , we speculate that the reaction proceeds along the pathway presented in Scheme . First, Pd (0) inserts into the O–H bond of 2a via oxidative addition to form Pd­(II)-H species I .…”

“…To our delight, 1-naphthols could also be tolerated in this protocol. It is worth noting that 1-naphthols have never been reported as effective nucleophiles in previous reported studies on 1,3-diene hydrofunctionalizations. − Commercially available 1-naphthols 2i and 2j containing a methoxyl group at the C7 position reacted smoothly to furnish the corresponding allylic substitution products ( 3ai and 3aj ) in good yields (78% and 61%, respectively). In addition, polyfunctionalized electron-enriched phenols 2k , 2l , and 2m furnished the expected product 3ak , 3al , and 3am in decent to good yields (61%–84%).…”

“…Later, Liu and Zhang et al realized a triflic acid-catalyzed highly para -selective allylic alkylation of phenols with 1,3-dienes . During the preparation of this work, Yin’s group reported an elegant Ni/Brønsted acid dual-catalyzed regioselective C–H functionalization of phenols with 1,3-dienes, and TsOH has proved to be a necessary additive to enable the reaction to occur in this case . Despite these advances, the development of transition-metal catalytic systems for the site- and chemo-selective C–H bond hydrofunctionalization of phenols with 1,3-dienes remains underexplored and highly desirable.…”

Understanding the Regiodivergence between Hydroarylation and Trifluoromethylarylation of 1,3-Dienes Using Anilines in HFIP

“…As a step forward, one of the first examples of nonprefunctionalized aryl substrates relied on indoles using rhodium complexes with carbodicarbene ligands; it was first used in a racemic protocol and, later on, extended to its enantioselective version. − Soon after, benzamides were incorporated in a C–H activation process triggered by an iridium catalyst where the amide serves as a directing group . Recently, phenols engaged in this transformation in a process catalyzed by palladium or nickel complexes, triflic acid, or triarylboranes. − The latter approach was expanded to diarylamines that also work under Ca­(II)/hexafluoroisopropanol (HFIP) conditions . A very recent contribution incorporates pyridines in an enantioselective catalytic transformation on the basis of a groundbreaking Ni–Al bimetallic system .…”