Phosgene ring closure with

Several 1,3-dioxoperhydropyrrolo[l,2-c]oxazoles (266) have been synthesized. The more common procedure is by reaction of C-substituted prolines (264) with phosgene, followed by ring closure with 2,6-lutidine <83JPS(A)1699> or Ag20 (Scheme 46) <83Mi 802-oi>. 

Over eighty N-aryl oxadlazolones were synthesized by a procedure described by Boesch in a German patent (15). This consists of reacting aryl hydrazines with a chloroformic ester followed by ring closure with phosgene. Representative structures are listed in Table 2. 

In an extension of the Niementowski synthesis, it was found that 4-quinazolones could be also be synthesized via an isatoic anhydride intermediate/ Isatoic anhydride has been prepared from anthranilic acid using either phosgene or ethyl chlorocarbonate. Clark and Wagner reported that when isotoic anhydride 38 was heated with a primary amine and triethyl orthoformate, 39 was formed. The reaction likely proceeds by way of initial attack of the amine on the carbonyl group at the 4-position of 38 to form the corresponding anthranilamide followed by ring closure with triethyl orthoformate. If triethyl orthoformate is not added to the reaction mixture, the anthranilamide that is formed can be isolated and used as an intermediate for the synthesis of quinazolones by various methods. ... 

An excess of phosgene is used during the initial reaction of amine and phosgene to retard the formation of substituted ureas. Ureas are undesirable because they serve as a source for secondary product formation which adversely affects isocyanate stabiUty and performance. By-products, such as biurets (23) and triurets (24), are formed via the reaction of the labile hydrogens of the urea with excess isocyanate. Isocyanurates (25, R = phenyl, toluyl) may subsequendy be formed from the urea oligomers via ring closure. 

This approach is suitable for the formation of mesoionic 1,3,4-thiadiazoles. The thiohydrazide (427) with phosgene, thiophosgene or an isocyanide dichloride leads to ready ring closure and formation of the mesoionic 1,3,4-thiadiazoles (428 X = 0, S, NR, respectively) (b-79MI40300). 

The treatment of 5-(a-hydroxy)ethyl-6-aminoacenaphthene with phosgene in boiling benzene leads to the ring closure of 3,1-oxazepine (66ZOR148). The partially hydrogenated derivative 517 is formed as the... 

A number of 3-amino-s-triazolo[4,3-a]pyrazines (122) have been prepared by the action of cyanogen chloride on hydrazinopyrazines. The latter compounds also undergo ring closure to s-triazolo[4,3 a]-pyrazines on treatment with phosgene, carbon disulfide, and triethyl orthoformate.331-336... 

Compound 1216 was then reacted with allylamine in the presence of Et3N to give A, A -diallyl-9//-carbazole-3,6-dicarboxamide 1217, subsequent treatment of compound 1217 with phosgene gave 3,6-dicarboximidoyl dichloride derivative 1218. Ring closure of dichloride 1218 was carried out under basic conditions to give 9-ethyl-3,6-di(l//-pyrrol-2-yl)-9//-carbazole 1219, a relatively low oxidation potential monomer with electron-rich pyrrole rings as terminal electropolymerizable moieties, in an overall synthetic yield of 5.8%. 

A 2- or 6-hydroxy-substituted purine can be prepared from the corresponding 4,5-diamino-pyrimidinol by cyclization with an acid, ester, ortho ester, or amide. If the ring closure is performed with reagents such as urea, alkyl chloroformates, urethanes, phosgene, and alkyl isocyanates, the 8-hydroxypurines are formed. Various xanthine and uric acid derivatives have been prepared by the condensation of 5,6-diaminopyrimidine-2,4-diols with formic acid. Purin-2-ol (1) was prepared by this route from 4,5-diaminopyrimidin-2-ol and ethyl orthoformate. ... 

H-3,1-Benzoxazine-2,4(1 H)-dione known as isatoic anhydride (VI) is the most popular six membered cyclic O-acyl carbamate. The synthesis of isatoic anhydride by ring closure of anthranilic acid with phosgene is well described (Ref. 250). However, we have developed an... 

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