Reactivity of Carbenes and Ketenes in Low-Temperature Matrices. Carbene CO Trapping, Wolff Rearrangement, and Ketene−Pyridine Ylide (Zwitterion) Observation

Dicarbalkoxyketenes 8a and 8b are obtained by photolysis of diazo esters 7 in cryogenic matrices or by FVT of 7 followed by matrix isolation. The photochemical Wolff rearrangement of diazomalonates 1 in Ar matrix at temperatures as low as 6.5 K produces alkoxy(alkoxycarbonyl)ketenes 3, also obtained by FVT of 1. Photolysis of 1 in CO matrix at ≥6.5 K produces the dicarbalkoxyketenes 8. Ketenes 3, 8, and 12 react with pyridine above 40 K to produce ketene−pyridine ylides (zwitterions) 9, 10, and 13, respectively.