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Polyurethanes are the only class of polymers that display thermoplastic, elastomeric, and thermoset behavior depending on their chemical and morphological makeup. In addition to compact polyurethanes, foamed variations in particular are very widespread, and they achieve their targeted properties at very low weights. The simple production of sandwich structures and material composites in a single processing step is a key advantage of polyurethane technology. The requirement of energy and resource efficiency increasingly demands lightweight structures. Polyurethanes can serve this requirement by acting as matrix materials or as flexible adhesives for composites. Polyurethanes are indispensable when it comes to high-quality decorative coatings or maintaining the value of numerous objects. They are extremely adaptable and sustainable problem solvers for today's challenges facing our society, all of which impose special demands on materials.

The photo- and thermochemistry of diazo(2-furyl)methane (3) and diazo(3-furyl)methane (6) was investigated using the matrix isolation technique. Photolysis of 3 results in the formation of (Z)-pent-2-en-4-yn-1-al (2) in a clean reaction, in agreement with the observation of Shechter et al. Photolysis or pyrolysis of diazo compound 6 yields (s-Z)-(α-formyl)methylenecyclopropene (s-Z-13) as the only detectable product. Carbene 14 and cyclopropene 15 are proposed as intermediates, but not stable under the reaction conditions and thus not directly observed. The reaction sequence 613 provides a novel and simple route to methylenecyclopropenes.

Warming the dilithium salt 7 of furan-2,5-dicarboxaldehyde bis(tosylhydrazone) to 110°C and subsequently trapping the products in solid argon at 10 K resulted in the formation of 1-diazo-hex-3-en-5-yn-2-one (9). The intermediate 2,5-bis(diazomethylfuran) (6) is too labile to be directly observed under these conditions. The formation of 9 from 6 is rationalized by the loss of one nitrogen molecule and rapid rearrangement of the intermediate carbene 8. Photolysis of 9 leads to loss of the second nitrogen molecule and rearrangement of the resulting carbene 12. The major path is the Wolff rearrangement to hexa-1,3-dien-5-yn-1-one (11); the minor path is the intramolecular cycloaddition of the carbene center to the triple bond to 1H-bicyclo[3.1.0]hexa-3,5-dien-2-one (2). UV photolysis of 2 results in the ring opening to yield again ketene 11. The mechanism of this rearrangement was investigated by deuterium labeling.