The syntheses and flash vacuum thermolyses of 5-[(alkylamino)methylene]-2,2-dimethyl-1,3-dioxane-4,6-diones (Meldrum's acid derivatives) 13a-i are described. Thermolysis of 13a as well as of ethyl 3-(tert-butylamino)acrylate (22) gives a tautomeric mixture of cyanoacetaldehyde (14) and 3-hydroxypropenenitrile (15). Thermolysis of 13b gives iminoacrolein 26 and not cyanoacetone (29). Thermolysis of 13c,d gives S-methyl cyanothioacetate (30), and 13f-h give cyanoacetamides 31 in high yields. 2-Cyanopent-4-enoic acid derivatives 32 are obtained from Meldrum's acids 13e,i. The results are discussed in terms of facile 1,3-shifts of methylthio and alkylamino groups in imidoylketenes, interconverting imidoylketenes and acylketene imines.