Heterocumulenes react with lanthanoid reductants such as Yb metal, YbC
l3/Zn, and SmI2. In tetrahydrofuran (THF) or THF-hexamethylphosphoric
triamide (HMPA), diphenylketene (1) is reduced with Yb or YbCl3/Zn to
give dimeric compounds (2-5), whereas monomeric products (6-8) are obt
ained with SmI2, one-electron reductant. Isocyanates (11 a-g) are redu
ced with SmI2, to produce oxamides (12 a-g) in moderate to good yields
. This reaction proceeds via one electron transfer from SmI2, followed
by homocoupling of radical intermediates [H]. At room temperature 1-n
aphthyl isocyanate (11 e) is treated with SmI2 to give 1-naphthylamine
as a main product, while at lower temperature, corresponding oxamide
(12 e) is obtained as a main product. Higher temperature and longer re
action time are necessary to complete the reaction of aliphatic isocya
nates. Furthermore, the SmI2/THF/HMPA system desulfurizes isothiocyana
tes, R-NCS (13 a-c), under the mild conditions, to give isonitriles (1
4 a-c) in good yields, irrespective of the substituents (R). Thioketon
e (15) also undergoes desulfurization by Yb metal in THF-HMPA to give
olefin (16) at room temperature.