Formation of carbon-carbon single bonds from isocyanates and cyclic pentaoxyphosphoranes-VI

The reaction of 4,5-dimethyl-2,2,2-trimethoxy-2,2-dihydro-1,3,2-dioxaphospholene with carbomethoxy, carbopropoxy and N,N-diphenylcarbamyl isocyanates yields, respectively, 2-methoxy-, 2-propoxy- and 2- diphenylamino-5-acetyl-5-methyl-2-oxazolin-4-one. The reaction with carbophenoxy isocyanate gives two products in a proportion which depends on experimental conditions: 2-phenoxy-5-acetyl-5-methyl-2-oxalin-4-one (1:1 stoichiometry) and 1,3-dicarbophenoxy-5-acetyl-5-methyl-hydantoin (1:2 stoichiometry). The 2-substituted 4- oxazolones are hydrolyzed to 5-acetyl-5-methyl-oxazolidin-2,4-dione. The alkyl group of the 2-alkoxy-4-oxazolones migrates to the adjacent nitrogen to give 3-alkyl-5-acetyl-5-methyl-oxazolidin-2,4-diones. The dioxaphospholene reacts with 2-substituted 2-thiazolin-4,5-diones to give 2-substituted 5-acetyl-5-methyl-2-thiazolin-4-ones, including rhodanine derivatives.