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 greater than or equal to 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