10. Cyclization Reactions of Dianions
Dianions are twofold deprotonated organic compounds. They can be used as building blocks for the synthesis of a variety of carbo- and heterocyclic products which are of pharmacological relevance.
10.1 Synthesis and Reactions of 2-(Alkylidene)tetrahydrofurans
Abstract: 2-(Alkylidene)tetrahydrofurans are prepared by cyclization of 1,3-dicarbonyl dianions or 1,3-bis(silyloxy)-1,3-butadienes with various electrophiles. The products represent versatile building blocks for hydrogenation, cross-coupling, bromination and oxidation reactions.
Reviews: Tetrahedron 2007, 63, 10865-10888; Chem. Rev. 2004, 104, 4125-4149.
Period of investigation: 1999 – 2007
Keywords: 1,3-dicarbonyl compounds; dianions; silyl enol ether; cyclizations; heterocycles
10.2 Cyclizations of Dianions with Epihalohydrins
Abstract: Cyclization reactions of epichlorohydrin and epibromohydrin with free and masked dianions allow for a convenient synthesis of a variety of products, such as 2-(alkylidene)tetrahydrofurans, which can be further funcionalized by hydrogenation or ring transformation reactions, cyclopropanes, γ-butyrolactams, oxazines, oxazolo[3,4-b]pyridazin-7-ones or 2-(alkylidene)thiazolidines. In general, the reactions proceed with very good regioselectivity.
Review: Synlett 2023, 34, 1953-1960.
Period of investigation: 1999 - 2006
Keywords: dianions; 1,3-dicarbonyl compounds; cyclizations; silyl enol ethers
10.3 Cyclizations of Oxime and Hydrazone Dianions
Abstract: One-pot cyclizations of oxime and hydrazone dianions with various electrophiles provide an efficient synthesis of functionalized isoxazoles, pyrazoles and other heterocycles.
Review: Synlett 2011, 2633-2342.
Period of investigation: 2005 - 2015
Keywords: dianions; cyclizations; heterocycles
10.4 Chemistry of the Dianion of 1,1-Diphenylacetone
Abstract: Cyclizations of the dianion of 1,1-diphenylacetone allows for the synthesis of various heterocycles. From a study directed towards the regioselectivity of such reactions a new allene synthesis via allene dianions was found by serendipity. Reactions of allene dianions with various electrophiles were studied.
Review: Synlett 2023, 34, 414–422.
Period of investigation: 1993 - 2003
Keywords: allenes; cyclizations; dianions
10.5 Cyclizations of Bis-Imidoylchlorides of Oxalic Acid
Abstract: The cyclization of oxaldiimidoyl dichlorides, readily available novel building blocks, with ambident dianions and other bis(nucleophiles), such as diamines, provides a convenient access to a variety of heterocycles important in medicinal chemistry or materials science. Reactions include cyclization-, domino-, one-pot- and double-anion-capture-reactions.
Review: Eur. J. Org. Chem. 2002, 221-234.
Period of investigation: 1999 – 2006
Keywords: cyclizations; dianions; heterocycles