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.

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

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

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

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

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