(E)-2-(1-Cyano-2-methoxy-2-oxoethylidene)-3,4-dioxo-1- (pyridin-1-ium-1-yl)cyclobutan-1-ide
(E)-2-(1-Cyano-2-methoxy-2-oxoethylidene)-3,4-dioxo-1-(pyridin-1-ium-1-yl)cyclobutan-1-ide was obtained by a three-component reaction of squaric acid dichloride with pyridine and methyl cyanoacetate.