ChemInform Abstract: Cp*Co^III Catalyzed Site‐Selective C—H Activation of Unsymmetrical O‐Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes.

Abstract

The synthesis of isoquinolines by site-selective C À H activation of O-acyl oximes with aC p*Co III catalyst is described. In the presence of this catalyst, the CÀHa ctivation of various unsymmetrically substituted O-acyl oximes selectively occurred at the sterically less hindered site,and reactions with terminal as well as internal alkynes afforded the corresponding products in up to 98 %y ield. Whereas the reactions catalyzedbythe Cp*Co III system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp*Rh III catalysts led to low selectivities and/or yields when unsymmetrical O-acyl oximes and terminal alkynes were used. Deuterium labeling studies indicate ac lear difference in the site selectivity of the C À Ha ctivation step under Cp*Co III and Cp*Rh III catalysis.

Making Base-Assisted C–H Bond Activation by Cp*Co(III) Effective: A Noncovalent Interaction-Inclusive Theoretical Insight and Experimental Validation

“…[7][8][9][10] In contrast, the catalytic activity of Cp*Co(III) complexes has long been ignored and remained mostly unexplored until recently. The recent upsurge of publications dealing with the use of Cp*Co(III)-catalysts in C-H bond functionalizations [11][12][13][14][15][16] was triggered by the remarkable reports by Kanai and Matsunaga [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] (scheme 1) and by Ackerman et al [34][35][36][37][38][39][40][41][42][43][44][45] and followed by a number of other reports. 46,47 In many reported cases this powerful class of cobalt catalysts 11 presents reactivity profiles that differ from their rhodium and iridium analogues.…”

“…It is important to mention that known syntheses (scheme 1) of Cp*Co(III)-metallacycles are based on the use of sensitive Cp*Co(I)L2 (L=CO; Me3SiCH=CH2) complexes and rely on an oxidative addition step requiring expensive iodo-arene substrates such as 2-(2-iodophenyl)pyridine (oxidative addition). 53 A variant operating via electrophilic metallation inspired from the early applications to catalysis of Matsunaga and Kanai [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]48 makes use of [Cp*Co(III)(MeCN)3](BF4)2 56 and excess of 2-phenylpyridine, i.e 2-phpyH (scheme 1c). Another one proposed by Zhu et al 16,54 with Cp*Co(CO)I2 requires 2 eq of silver acetate to promote the formation of cobaltacycles (scheme 1d) with no evidence of the dominance of the CMD mechanism.…”

Synthesis of densely substituted pyridine derivatives from nitriles by a non-classical [4+2] cycloaddition/1,5-hydrogen shift strategy

“…1). Consequently, many synthetic methods have been developed to access this important class of N-heterocycles, including metal-free multicomponent syntheses, 18 transition metal-catalyzed [2 + 2 + 2] cycloaddition reactions [19][20][21][22][23][24][25] for pyridines, and transition metal-catalyzed annulations involving alkynes [26][27][28][29][30] for isoquinolines. Despite these advances, the lack of chemo-and regioselectivities in multicomponent reactions and requirement of complex functionalized substrates as well as harsh reaction conditions 22,31−33 often limits further exploitation of the synthetic potential of these approachs.…”

Cp*Co(III)-Catalyzed C–H Hydroarylation of Alkynes and Alkenes and Beyond: A Versatile Synthetic Tool

“…They observed that, due to the mentioned steric hindrance between the Cp* “hat” and the substituents on the substrate, high regioselectivities were achieved toward functionalization at the less sterically demanding position using [Cp*Co(CO)I 2 ] as a catalyst, whereas [Cp*RhCl 2 ] 2 led to no selectivity under various conditions. 17 Scheme 2 shows the different selectivities obtained with each catalyst for the reaction of substrate 4 bearing a chlorine atom at the meta position and phenylacetylene 5 . Thus, in most of the examples that will be described throughout this perspective article, when an unsymmetrically substituted substrate is used, functionalization takes place at the less hindered position.…”