Cobalt(I)-Catalysed Reactions for the Synthesis of Acyclic 1,4-Dienes - Genesis of Two Synthetic Methods

Abstract

The search for atom-economic carbon-carbon bondforming reactions initiated by low-valent cobalt complexes has led to two reactions that generate acyclic 1,4-dienes: the 1,4-hydrovinylation reaction of a terminal alkene with a 1,3-diene and the Alderene reaction of a terminal alkene with an internal alkyne.The regioselective cobalt-catalysed Diels-Alder reaction of an alkyne and a 1,3-diene for the synthesis of cyclic 1,4-dienes led to its application in the synthesis of 1,3-dicarbonyl derivatives upon ozonolysis. Through applications of the cobalt-catalysed 1,4-hydrovinylation reaction, the synthesis of 1,3-or 1,4-dicarbonyl derivatives can be accomplished in a substrate-controlled process. For instance, 2,3-dimethylbuta-1,3-diene leads to acyclic 1,4-dienes via the cobalt-catalysed 1,4-hydrovinylation reaction which can then be converted into 1,3-carbonyls by ozonolysis. In contrast, the use of 2-(trimethylsiloxy)buta-1,3-diene generates g,d-unsaturated ketones, which can be converted into 1,4-dicarbonyl derivatives upon ozonolysis. Recently, studies into the synthesis of different types of polycarbonyl compounds in which the distance between the carbonyl groups can be altered have been initiated.

Hydroxy‐Directed Ruthenium‐Catalyzed Alkene/Alkyne Coupling: Increased Scope, Stereochemical Implications, and Mechanistic Rationale

“…Herein we show how such secondary interactions can be used to render alkene/alkyne coupling of the Alder-ene-type stereoselective while increasing the substrate scope of this valuable transformation. [8][9][10] Ruthenium complexes such as [CpRu(MeCN) 3 ] + or [Cp*Ru(cod)Cl] are known to engender oxidative cyclization of alkenes and alkynes with formation of metallacycles,a nd lead to 1,4-dienes by selective elimination of the exocyclic b-Hatom. [8,[11][12][13] Thebroad scope of this reaction notwithstanding, it remains limited to the use of terminal olefins as substrates,e xcept for intramolecular and hence entropically favored cases.E ven amongst terminal olefins,t he use of 1,1disubstitued alkenes was accomplished only recently.T hey require acoordinating NHBoc group at the allylic position to assist in their binding to the catalyst.…”

Hydrovinylation Reactions – Atom‐Economic Transformations with Steadily Increasing Synthetic Potential

“…[2] Nevertheless, in some cases single isomers were obtained and the work done in this field for the selective intermolecular generation of 1,4-dienes will be presented.…”

“…It can be easily imagined that the search for suitable catalyst systems for the selective generation of all possible regioisomers and stereoisomers 9-16 will be challenging and of great academic interest. [2]…”

Cobalt-Catalysed Bond Formation Reactions; Part 2

“…Hydrovinylation is the process in which a C-H bond of an alkene acts as donor and undergoes an addition to another unsaturated group, such as a second alkene, which acts as acceptor (Scheme 21). 45 For this process, two scenarios are reported: a) the acceptor is an alkene -in this case a 1,2-hydrovinylation (1,2-HV) is encountered; and b) the acceptor is a 1,3-diene -these processes are called 1,4-hydrovinylation (1,4-HV) reactions.…”