Nickel Catalyzed syn-Selective Aryl Nickelation and Cyclization of Aldehyde/Enone-Tethered Terminal Alkynes with Arylboronic Acids

Abstract

A syn-arylative nickelation followed by nucleophilic syn-selective cyclization of o-propargyloxy benzaldehydes is achieved toward the synthesis of chromanol skeletons with alkenyl substitution at C3. The capture of the intermediate vinyl nickel in its cis geometry is done also with a Michael acceptor to synthesize 4-alkylated derivatives. This protocol is equally applicable to opropargylamino benzaldehydes to access 3,4-disubstituted tetrahydro-hydroquinolines.

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

“…However, certain heteroarylboronic acids that are less susceptible to protodeboronation (such as 3-furyland 3-thienylboronic acid), have been successfully employed. [61][62][63][65][66][67][68][69][70][71][72][73][74][75]113] The use of alkenylboron reagents in these reactions have also been described [see Tables 7, and Equation ( 41)] [66,70,75] although low yields are often observed because of competitive protodeboronation. To our knowledge, no examples of nickel-catalyzed alkylative cyclization using alkylboron reagents have been reported.…”

“…More recently, nickel catalysis has also been shown to be highly effective in these reactions. [61][62][63][64][65][66][67][68][69][70][71][72][73][74][75] As well as being less expensive and more readily available than the more commonly used rhodium or palladium catalysts, nickel catalysis can offer unique possibilities in reaction development not readily available to these other catalyst systems. [76][77][78][79][80][81][82][83][84][85][86][87][88][89] This review will describe nickel-catalyzed arylative cyclizations of alkyne-and allene-tethered electrophiles using arylboron reagents, that proceed by the general mechanistic pathways shown in Scheme 1.…”

“…By varying the tether or the electrophile of the substrate, a variety of cyclic products can be obtained, and by employing non‐racemic chiral ligands, enantioselective reactions can be achieved. More recently, nickel catalysis has also been shown to be highly effective in these reactions [61–75] . As well as being less expensive and more readily available than the more commonly used rhodium or palladium catalysts, nickel catalysis can offer unique possibilities in reaction development not readily available to these other catalyst systems [76–89] …”

An Unconventional trans - exo -Selective Cyclization of Alkyne-Tethered Cyclohexadienones Initiated by Rhodium(III)-Catalyzed C–H Activation via Insertion Relay

“…In view of the appealing reactivity of alkynes, 4,5 transition metal-catalyzed cascade cyclization reactions of alkyne-tethered electrophiles have been extensively investigated over the past decades. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] As shown in Scheme 1a, the elementary cis-insertion of alkyne by organometallic species usually adopts the following two ways: α-insertion or β-insertion. The electronic and sterically unbiased alkynes usually undertake cis-β-insertion to form intermediates I, which can subsequently cyclize in cis-exo-fashion to furnish conventional products II possessing an exocyclic double bond (Scheme 1a, Path A).…”

“…This cascade cis-β-insertion and cis-exo -cyclization pathway have been well studied for various alkyne-tethered electrophiles (aldehyde, ketone, imine, ester, isocyanate, nitrile, alkene, alkyne, etc.) using rhodium, [6][7][8][9][10] palladium, [11][12][13] and other transition metals [14][15][16][17][18][19][20] as catalysts. On the other hand, alkynes bearing aryl or silyl groups at R 1 substituents prefer to choose cis-insertion of the alkynes at the α-position to offer the alkenyl metal intermediates III (Scheme 1a).…”