Nickel‐Catalyzed Arylative Cyclizations of Alkyne‐ and Allene‐Tethered Electrophiles using Arylboron Reagents

Abstract

The use of arylboron reagents in metal-catalyzed domino addition-cyclization reactions is a well-established strategy for the preparation of diverse, highly functionalized carbo-and heterocyclic products. Although rhodium-and palladium-based catalysts have been commonly used for these reactions, more recent work has demonstrated nickel catalysis is also highly effective, in many cases offering unique reactivity and access to products that might otherwise not be readily available. This review gives an overview of nickelcatalyzed arylative cyclizations of alkyne-and allene-tethered electrophiles using arylboron reagents. The scope of the reactions is discussed in detail, and general mechanistic concepts underpinning the processes are described.

Endo-Selective Intramolecular Alkyne Hydroamidation Enabled by NiH Catalysis Incorporating Alkenylnickel Isomerization

“…With this reaction design, another requirement for the desired transformation was to achieve a predictable regiocontrol for the first hydronickelation step. In this regard, it is well known that aryl-substituted alkynes undergo a selective migratory addition, with Ni being typically inserted adjacent to the aryl group. − Although the ability to incorporate substituents other than aryl groups is highly sought after (vide infra), optimizations for the designed process were carried out by employing such a substrate-control approach to establish general conditions first. Consequently, phenyl-substituted alkynyl dioxazolone 3 was chosen for the initial screenings to access six-membered lactam scaffolds that would be challenging to obtain by the previous strategies (Table ).…”

“…To this end, we conceived an alternative inner-sphere − approach based on NiH catalysis, − which would allow us to define the bond-forming carbon site prior to the cyclization, in a highly predictable manner (Scheme c). With hydronickelation known to take place commonly by syn addition, one imperative requisite for this reaction design would be the ability to incorporate alkenylnickel E / Z isomerization. − This unique mechanistic handle has in fact been broadly utilized for C–C bond-forming cyclization, − but scarcely for the C–N equivalents. Although a few examples have been reported for intramolecular arylative amination of alkynes with azides, these reactions are specific to highly activated structures that are prone to further aromatization to rather give unsaturated heteroarenes. , Thus, the development of new alkenylnickel isomerization strategy for delicately controlled endo -selective amidative cyclization would be extremely appealing.…”

“…The new development enables the regioselective access to six- to eight-membered endocyclic enamides, thus granting ring sizes and selectivity that were beyond reach with the previous strategy . The reaction is broad in scope and shows excellent regioselectivity even for the substrate classes underrepresented in alkenylnickel isomerization chemistry, such as alkynyl- and alkyl-substituted alkynes. − Comprehensive experimental and computational investigations suggested that Ni­(I) catalysis is operative in the current process, and the key alkenylnickel isomerization is likely involved via an η 2 -vinyl-like transition state. The obtained endo selectivity was proven beneficial in terms of synthetic virtues, as the versatile enamide functionality within the rings could be subsequently harnessed for a number of diastereoselective transformations to lead to highly functionalized δ-lactam scaffolds.…”

Construction of a Pentacyclic Framework Enabled by Nickel Catalysis

“…Aryl nickelation of alkynes has been explored for arylative cyclization through an alkenyl–Ni intermediate to yield different types of (hetero)­cyclic compounds by the intramolecular nucleophilic attack . In this work, we designed a cascade approach utilizing (het)­aryl boronic acid to transform an easily available indole-containing substrate into a complex pentacyclic system in a single step (Scheme c).…”

Rhodium-catalyzed formal [2 + 2 + 1] annulation of arylboronic acids with alkynes

“…6 Despite these great advances achieved, novel transformations between arylboronic acids and alkynes, especially those that can sequentially construct multiple C–C bonds in a single step, are still underdeveloped. 7…”