FVT of 2-(2-diazoacetyl)pyridine (1) yields 2-pyridylketene (3) (largely in the s-Z form 3Z), which dimerizes to quinazolinone 5. Matrix photolysis of 1 (largely in the EZ form 1EZ) yields the carbene−pyridine ylide 6, which on further photolysis at λ > 320 nm is converted to (mainly) the s-E ketene 3E. Continued photolysis of 3E at 320 nm converts it to 3Z, and this process is reversed on photolysis at 254 nm.

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Organic pigments are important crystalline substances, and their properties and applications rely on size and shape control. Pigment Yellow 181 (PY181) is an industrial azo pigment that is light and weatherfast and suitable for high temperature processing. One disadvantage is its needle‐like shape in the default β‐phase, which makes the pigment difficult to process in industry, e.g., in polymer melts, where a spherical structure would be ideal. Here, we show for the first time, that polymer‐induced liquid precursor structures can be formed even in association to a chemical reaction. Furthermore, it is demonstrated that biomineralization principles can be exploited for the generation of advanced functional materials, such as pigments with novel complex morphology and different properties. Stable PY181 microspheres of nanoplates in the β‐phase were obtained in mixed solvents of water and isopropanol by direct azo coupling under the directing influence of a designed copolymer additive aminobenzoylaminobenzamide‐acetoacetyl‐poly(ethylene imine)‐block‐poly(ethylene glycol) (ABABA‐acetoacetyl‐PEI‐b‐PEG).

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2-Pyridyl)iminopropadienone 13 is generated by flash vacuum thermolysis (FVT) of 2-substituted pyrido[1,2-a]pyrimidin-4-ones 9 and observed by IR spectroscopy. Addition of HCl to 13 causes reversion to the starting material 9b, whereas addition of nucleophiles leads to malonic acid imide derivatives (23, 24, 26, 27, 28). The latter undergo thermal elimination of amines to regenerate 2-substituted pyridopyrimidinones. A competing retro-ene reaction occurs on FVT of 2-(dialkylamino)pyridopyrimidinones 9c,d, presumably in the oxoketenimine intermediates 22/25, with formation of the unsubstituted pyridopyrimidinone 31.