Imidization, cyclizing

Figure 5.31 Amic acid formation and imide cyclization.

Imide aryl ether ketone segmented block copolymers, 360 Imide chemistry, 292-295 Imide cyclization, 301 Imide exchange, polyimide syntheses by, 268... 

In a similar manner N-imidoylnitrile imides afford 1,2,4-triazoles ( ), and N-thioacylnitrile imides cyclize to yield 1,3,4-thiadiazoles ( ). 

Fig. 2. Cyclization of amic acid to imides or isoimides via (12). Formation of the mixed anhydride intermediate (12) is shown in text.

Guareschi imides are useful synthetic intermediates. They are formed from a ketone reacting with two equivalents of the cyanoacetic esters and ammonia. This transformation is illustrated in the formation of 4,4-dimethylcyclopentenone 30.The synthesis was initiated with the Guareschi reaction of 3-pentanone 27 with 28 to generate imide 29. This product was hydrolyzed to the diacid and esterified. Cyclization of the diester via acyloin condensation followed by hydrolysis and dehydration afforded the desired target 30. 

An ingenious synthesis of 1-arylisoindolcs has been developed by Vebor and Lwowski, based upon the reaction of an o-phthalimido-methylbenzophenone (41, R = aryl) with hydrazine (Table IV). The benzophenone is prepared by a Friedel-Crafts reaction with o-phthalimidomethylbenzoyl chloride (40). The mechanism of isoindole formation can be represented sehematically by a sequence involving attack by hydrazine at the imide to give the ring-opened hj drazide (42), followed by cyclization to phthalazine-l,4-dione (44) with displacement of the o-aminomethylbenzophenone (43). Intramolecular condensation of the latter can lead, via the isoindolenine... 

Reaction of anthanilic acid 112 with acid anhydrides afforded the corresponding imide derivatives 113. Subjecting 113 to intramolecular Wittig cyclization has been achieved by treatment with A-phenyl(triphe-nylphosphoranylidene)etheneimine in toluene or dioxane whereby the corresponding pyrroloquinolines 116 were obtained (94TL9229). The intermediate 115 resulting from the rearrangement of 114 could be isolated when the reaction was done at room temperature (Scheme 22). 

The Parham cyclization of the iodinated imide 270 by BuLi in dry THF at —78°C afforded 1 lZ -hydroxy-l,3,4,6,7,l lZ -hexahydro[l,4]oxazine[3,4-a]iso-quinolin-4-one 258 (97JOC2080). Iodide-lithium exchange was faster then addition to the carbonyl group of imide 270 and intramolecular cyclization of the initially formed anion gave compound 258. 

In an effort to identify a more stereoselective route to dihydroagarofuran (15), trimethylsilylated alkyne 17 was utilized as a substrate for radical cyclization (Scheme 2). Treatment of 17 with a catalytic amount of AIBN and tri-n-butyltin hydride (1.25 equiv) furnishes a mixture of stereoisomeric vinyl silanes 18 (72% combined yield) along with an uncyclized reduction product (13% yield). The production of stereoisomeric vinyl silanes in this cyclization is inconsequential because both are converted to the same alkene 19 upon protodesiiyiation. Finally, a diastereoselective di-imide reduction of the double bond in 19 furnishes dihydroagaro-... 

The amidines 10, prepared by condensation of the corresponding imidates with aminoacetal-dehyde dimethyl acetal, undergo cyclization with a variety of acids to l//-3-benzazcpin-2-amines 11 45 Method A has proved to be successful on an industrial scale. 

Photosensitive functions are in many cases also heat sensitive, so the preparation of photosensitive polyimides needs smooth conditions for the condensations and imidization reactions. Some chemical reactants, which can be used for polyamide preparation, have been patented for the synthesis of polyimides and polyimide precursors. For example, chemical imidization takes place at room temperature by using phosphonic derivative of a thiabenzothiazoline.102 A mixture of N -hydroxybenzotriazole and dicyclohexylcarbodiimide allows the room temperature condensation of diacid di(photosensitive) ester with a diamine.103 Dimethyl-2-chloro-imidazolinium chloride (Fig. 5.25) has been patented for the cyclization of a maleamic acid in toluene at 90°C.104 The chemistry of imidazolide has been recently investigated for the synthesis of polyimide precursor.105 As shown in Fig. 5.26, a secondary amine reacts with a dianhydride giving meta- and para-diamide diacid. The carbonyldiimidazole... 

The thermal imidization of a polyamic acid film (PMDA-ODA or BPDA-ODA) obtained by casting an NMP solution leads to an amorphous polyimide. Two different teams have shown that a polyamic acid solutions in NMP heated at 200°C for a short time (20 min) gives polyimide particles fully cyclized and highly crystalline, as shown by X-ray diffraction and solid 13C NMR spectroscopy.151152 The chemical imidization of the same solution gives only amorphous particles. The difference between the cyclization of a solution and a casted film in the same solvent is intriguing. In the case of the solution, the temperature and the heating time are lower than in the case of the casted film as a consequence, a less organized structure would be expected for the particle. 

The films were then thermally cycled at tOO, 200 and 300°C for an hour at each temperature in a forced air convection oven to complete the cyclization. The solution imidization procedure has been further described by Summers, et. al. (42,43). A representative structure for the poly(imide siloxane) copolymers is depicted in Figure 5. 

In 1975, van der Baan and Bickelhaupt reported the synthesis of imide 37 from pyridone 34 as an approach to the hetisine alkaloids, using an intramolecular alkylation as the key step (Scheme 1.3) [23]. Beginning with pyridone 34, alkylation with sodium hydride/allyl bromide followed by a thermal [3,3] Claisen rearrangement gave alkene 35. Next, formation of the bromohydrin with A -bi omosuccinimide and subsequent protection of the resulting alcohol as the tetrahydropyranyl (THP) ether produced bromide 36, which was then cyclized in an intramolecular fashion to give tricylic 37. 

Complex imide 169 was prepared during an investigation into the preparation of analogues of the antiviral compound zanamivir Cyclization of imide 169 in acidic media, followed by treatment with trifluoroacetic acid, gave the corresponding 1,2,4-triazole 170 in a yield that was reported to be high (Equation 54) <1997BML2239>. 

Aminopyrazoles 257 substituted at the C-4 and C-5 positions react with a variety of imidate hydrochlorides giving iV-hydroxyamidines 258, that after tosylation and intramolecular cyclization afford the corresponding pyrazolo[ 1,5-4 )-[l,2,4]triazole derivatives 259 (Scheme 21) <1998CPB287, 1998CPB69>. 

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