Alkene Hydroamination via Earth‐Abundant Transition Metal (Iron, Cobalt, Copper and Zinc) Catalysis: A Mechanistic Overview

Abstract

This review gives am echanistic overview of the most relevant advancesi nt he area of alkene (formal) hydroamination promoted by earth-abundant transitionm etal catalysts involving iron, cobalt, copper and zinc. Focus will be on catalytic systems for which in depth investigations have been conducted to elucidate the activation pathwaya nd operating mechanism. Ther elevant literature has been covered from 2012u ntil early2 019. 1I ntroduction 2M echanism Overview 3A lkeneA ctivation Pathways 3.1 p-Coordination 3.2 Hydrometalation 3.3 H-Atom Tr ansfer 4A mine Deprotonation Pathway 5C onclusionScheme 5. Proposed mechanism for the DTBM-SEG-PHOS·CuH-catalyzedh ydroamination of styrene and Bn 2 NOCOAr proceeding by alkene hydrometalation [L 1 = (R)-DTBM-SEGPHOS].Scheme 7. Proposed metal hydride H-atom transfer (HAT) mechanism of iron-promoted formal hydroamination of nitro(hetero)arenes and (poly)substituted alkenes.

Hydroelementation of diynes

“…A limited number of chemical transformations leading to the formation of the C-N bonds in stoichiometric reactions led to the intensive development of hydroamination reactions, which simply introduce the N-atom to the compound structure, and occurs by the addition of the N-H bond to the unsaturated C-C bonds in olefins and alkynes. [19][20][21][22]29,[289][290][291][292][293] This 100% atom economic method mostly requires the application of a catalyst to (i) overcome the repulsion electrostatic effect between the high electron-dense unsaturated CRC bond and the strong Lewis base (electron-rich amine 11 or 21, ammonia, or hydrazine), and (ii) to facilitate this addition reaction due to the high energy difference between both types of bonds. 294 The hydroamination of (non)conjugated diynes leads to various products, but intramolecular cyclisation is of utmost importance to produce N-heterocyclic compounds, e.g., indoles, pyrroles, pyrazoles, pyrimidines.…”

“…127 The obtained products were further transformed into silyl-functionalised ketones 24 or enynes 22-23 with the above-described procedure (Scheme 6). 126 These alkylboryl-substituted enynes (16,21) are difficult to handle due to their low stability, therefore the hydroboration of diynes with alkoxyboranes (e.g., pinacolborane 25 or cateholborane 26) is much more desirable. Moreover, alkoxyboranes are easy to use and non-flammable.…”

Electrophilic Aminating Agents in Total Synthesis

“…Hydroamination of alkenes and alkynes is ap owerful strategy for the formation of CÀNb onds.Such processes are complementary to aza-Heck reactions because the product is generated at alower unsaturation level. Avariety of strategies have emerged for effecting alkene and alkyne hydroaminations,i ncluding metal- [198][199][200][201][202][203][204][205][206][207][208][209][210][211] and Bronsted acid catalyzed [212][213][214] methods,r adical-mediated processes [215][216][217][218][219] and pericyclic-based methods. [220,221] Conventional hydroamination protocols are designed to enable the addition of an amine NÀHbond across an alkene or alkyne p-bond.…”

Metal-Catalyzed Intermolecular Hydrofunctionalization of Allenes: Easy Access to Allylic Structures via the Selective Formation of C–N, C–C, and C–O Bonds

“…While this type of transformation has been accomplished with organocatalysis in some seminal works, the use of metal catalysts remains the most developed strategy for obtaining both selectivity and efficiency. [16][17][18][19][20] The aim of this review is to highlight the potential of hydrofunctionalization of allenes for the formation of C-N, C-C and C-O bonds and to give an exhaustive overview of the current knowledge in this field. The need of a comprehensive review is strengthened by the rate at which new catalytic systems and new conditions have been described in this area in the past few years.…”