Synthetic applications of cationic iron and cobalt carbonyl complexes

Abstract

Metal carbonyl stabilized cationic species react with a wide range of nucleophiles under mild conditions, and have thus found many synthetic applications. In this Perspective, we describe the utility of iron carbonyl dienyl cations in solution and solid phase parallel synthesis, and in the development of a new synthetic route towards oseltamivir phosphate (Tamiflu). We also discuss the solid phase version of the Nicholas reaction, employing cobalt carbonyl stabilized propargylic cations, and giving access to substituted alkynes.

Cobalt-Catalysed Bond Formation Reactions; Part 2

“…The recent advances in the field of propargylic nucleophilic substitution reaction, also called Nicholas reaction, will be summarised in the following. 178 The substitution of a leaving group, such as propargylic acetate, with heteroatom-and carbon-based nucleophiles is highly chemoselective in that it avoids the formation of allenes. Recent investigations of heteroatom nucleophiles involve the formation of bispropargylic ethers, 179 cyclic polyethers, 180,181 propargylic azides, 182 dithia-and thia-oxacyclooctynes, 183 seven-and eight-membered cyclic ethers 184 and carbacycles [185][186][187] with a cobalt-protected triple bond as well as the formation of 5-alkynylproline derivatives.…”

Fused Arene Ring Construction Around Pyrrole To Form 4,7‐Disubstitued Indole

“…Previously, we used these ethyne derivatives for introducing the ethyne unit into the porphyrin-like skeleton 20-thiaethyneporphyrin. [32][33][34][35][36][37][38] A direct reaction between 1,4-diaryl-2-butyne-1,4-diol 3a-c or 1,4-di-(thien-2-yl)-2-butyne-1,4-diol 3d and pyrrole (in excess) catalyzed with TFA (trifluoroacetic acid) failed to produce 2ac or 2d but produced trace amounts of 4,7-disubstituted indoles 1. [30,31] Subsequently, the modified Nicholas reaction was applied (Scheme 1).…”

“…[30,31] Subsequently, the modified Nicholas reaction was applied (Scheme 1). [32][33][34][35][36][37][38] A direct reaction between 1,4-diaryl-2-butyne-1,4-diol 3a-c or 1,4-di-(thien-2-yl)-2-butyne-1,4-diol 3d and pyrrole (in excess) catalyzed with TFA (trifluoroacetic acid) failed to produce 2ac or 2d but produced trace amounts of 4,7-disubstituted indoles 1. Subsequent reaction with pyrrole as a nucleophile followed by decomplexation afforded substituted alkynes, that is, 2a-d.…”

Selective Iron-Mediated C- and O-Addition of Phenolic Nucleophiles to a Cyclohexadiene Scaffold Using Renewable Precursors

“…Iron has the ability to coordinate dienes, , a feature that can be exploited for synthetic purposes. Upon coordination, the carbon atoms adjacent to the diene are activated for hydride abstraction, resulting in the formation of a stable cationic iron carbonyl dienyl cation. , The cationic iron carbonyl complex formed is bench stable, with a long shelf life, and can react with a wide range of nucleophiles to form carbon–carbon or carbon–heteroatom bonds. , This nucleophilic coupling with iron complexes occurs in a highly regio- and stereoselective manner. The regioselectivity of the initial cation formation is governed by the substitution pattern of the diene.…”