2-Oxo-l,3-heterocyclics

Analogously to conventional reactions 201-203), bis(trimethylsiloxy) alkenes form heterocycles of different classes l,2-bis(trimethylsiloxy)-l-cyclohexene (305) reacts with formamide urea malodinitrile and ethyl (J-amino-crotonate to afford 4,5,6,7-tetrahydrobenzunidazole (309) ° 2-oxo-l, 3,4,5,6,7-hexahydrobenzimidazoIe (317) , 2-aniino-3-cyano-4,5,6,7-tetra-hydro-coumarone (312) and 2-methyl-3-ethoxy-carbonyl-4,5,6,7-tetrahydro-in-dole (373) respectively. 

Trialkyloxonium ions are strong alkylating agents and initiate the polymerization of heterocyclic monomers by simple alkylation of the most nucleophilic site of the monomer. The initiation occurs quantitatively and without side reactions when stable anions are used. Consequently, these initiators are very useful for kinetic measurements. The initiation was followed directly by NMR spectroscopy in the case of THF (41). cyclic sulfides (42). and cyclic esters of phosphonic acid such as 2-methoxy-2-oxo-l,3,2-dioxaphosphorinane (43). 

Pseudoephedrine reacts via the classical Atherton-Todd reaction with dimethyl H-phosphonate to give the corresponding amidophosphate, which undergoes stereoselective heterocyclization to give 2-methoxy-3,4-dimethyl-5-phenyl-2-oxo-l,3,2-oxazaphos-pholane 1 in 82% yield based on the amidophosphate [118]. 

Maria, P.C., Elegant, L., Azzaro, M. et al. (1971) Phosphorus-containing heterocycles. X. Properties of a series of 2-oxo-l,3,2-dioxaphosphorinanes toward boron trifluoride. Measurement of the addition enthalpies. Bull. Soc. Chim. Fr, 3750-3753. 

Reaction of various aromatic or heteroaromatic diamines with iV-acyl isothiocyanates gave the corresponding benzo- or heterocycle-fused l,3,5-triazepine-2-thiones, for example, 16 (Figure 3) from 5,6-diamino-1,3-dimethyl-uracil and D-gluconyl isothiocyanate <1981CPB1832>. Cycloaddition of iVjiV -disubstituted ethylenediamines with bis(isocyanato)dimethylsilane or bis(isothiocyanato)dimethylsilane followed by treatment with 1,1 -carbonyldi-imidazole or 1,1 -thiocarbonyldiimidazole afforded a series of 1,5-disubstituted l,3,5-triazepine-2,4-diones, -2,4-dithiones, and 4-oxo-l,3,5-triazepine-2-thiones <1980AGE327>. 

Oxo-l,3-pyridothiazines. Most work on TAs fused with heterocycles has been devoted to 4-oxo-l,3-pyridothiazines. A number of pyrido-TAs 166 were obtained from 2-chloronicotinamide and thioesters in the presence of sodium hydride (89T4153) (Scheme 57). The role of sodium hydride consists in eliminating a proton from the amide group the resulting N-anion attacks the thiocarbonyl function, forming intermediates 165 whose cyclization gives pyrido-TAs 166. 

Aryl-5-oxo-3-trifluoromethyl-6,7-dihydroimidazo[2,3Y]l,3,5-thiadiazines 333 are formed by addition of 2-imidazoline thione 331 to 4-nitrophenyl-Y-alkylideneurethane 330. A requirement for the heterocyclization is the ability of the urethanes to generate intermediates 332 (Scheme 68) <2004CHE241>. 

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