Darstellung und Reaktionen von Thiooxalsäuren und Thiooxalsäurederivaten

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Abstract
In this review the chemistry of sulphur-containing oxalic acid derivatives is summarized from the synthetic point of view. Thiooxalic acid derivatives can be prepared in the following ways: Thiooxalic acid derivatives are active and useful C2 synthons. The incorporation of sulphur atoms in oxalic esters increases their reducibility. 1,1-Dithiooxalic acid esters and amides, dithionooxalic acid esters, and, especially, tetrathiooxalic acid dimethyl ester are attacked by S- and C-nucleophiles at the thiono group (thiophilic attack) to form the oxidation stage of a thioaldehyde or sulphides, respectively. In cycloaddition reactions oxalic acid derivatives with one thiono function react as 2π-systems whereas dithiono- and tetrathio-esters may function as 2π- as well as 4π-systems. In comparison to their O-analogues thionooxalic acid derivatives possess a higher reactivity towards nucleophiles. Heterocyclic compounds are obtained with bis-nucleophiles, e.g. quinoxalines, thiadiazoles, triazoles, peremidines, benzazoles, bisazoles, isoxazolones, and triazinones. With electrophiles or bis-electrophiles cyanodithioformic acid and compounds with a thioamide structure yield a variety of heterocycles (e.g. 1,2-dithioles, 1,2-dithioles-1,2-dithioles, thiazolothiazoles, thiazolidines, thiazolines, thiazoles, polythiazoles, dithiazoles, thiazinones, and imidazolinones). The results of UV-Vis, IR, ESR, and NMR investigations are summarized.