New Synthesis of Quinoxaline Derivatives Based on Palladium Catalyzed Oligomerization of 1,2-Diisocyanoarenes

Various 2,3-disubstituted quinoxaline derivatives were synthesized from monomeric and oligomeric (8substituted quinoxaline-2-yl)palladium(ll)s, which were prepared by the reaction of odiisocyanoarenes with trans-bromo(methyl)bis(phosphine)palladium(ll).Insertion reaction of carbon monoxide as well as isonitrile with organometallic compounds is fundamental, but important in organometallic chemistry.'Especially, most synthetic reactions with carbon monoxide catalyzed by transition metal complexes involve the insertion reaction as a key step in the catalytic cycles.However, unlike carbon monoxide, isonitriles are able to undergo multiple, successive insertion into carbon-metal linkage of organometallic compounds.2It has been well known that polymerization of isonitriles is catalyzed by some transition metal complexes to give poly(N-substituted iminornethylene)~.~The successive insertion of isonitriles with transbromo(methyl)bis(phosphine)palladium(ll) provides a product of triple isonitriles insertion, which are stabilized by intramolecular che~ation.~Recently, we found that the successive insertion of the two isocyano groups on odiisocyanobenzenes was completely controlled with trans-bromobis(dimethylphenylphosphine)methylpalladium(ll) to afford trans-bromobis(dimethylphenylphosphine)(3-methylquinoxaline-2yl)palladium(ll), which underwent further insertion of o-diisocyanobenzene, ultimately leading t Dedicated to the memory of the late Professor Yoshio Ban.