Benzoxazoles carboxylic acid amide

Reactions with carboxylic acid amide hydrochlorides Benzoxazoles from o-aminophenols Selective N-acylation... 

Those polyester FBAs containing a benzoxazole group are usually prepared from the appropriate o-aminophenol and carboxylic acid (11.45 Y = OH) or one of its derivatives, as shown in Scheme 11.10. The reaction proceeds via an intermediate amide and it can be advantageous to start from an acid derivative such as the acid chloride (11.45 Y = Cl) or ester (11.45 Y = OEt), which are both more effective acylating agents. The preparation of compound 11.36, shown in Scheme 11.11, illustrates this process, but the optimum conditions for ring closure vary considerably from one structure to another. The article by Gold contains a valuable and detailed summary [4]. 

Thermal dehydration of o- (acylamino)phenols is the method of choice for the preparation of benzoxazoles (equation 96) and other annulated oxazoles. 0,iV-Diacyl derivatives of o-aminophenols cyclize at lower temperatures than do the monoacyl compounds. The synthesis is often carried out by heating the aminophenol with the carboxylic acid or a derivative, such as the acid chloride, anhydride, an ester, amide or nitrile. The Beckmann rearrangement of oximes of o-hydroxybenzophenones leads directly to benzoxazoles (equation 97). 

Benzoxazoles are found in a variety of natural products and routinely find use in pharmaceutical research. They are generally made by condensation of a 2-aminophenol with a carboxylic acid or oxidative cylization of an imine intermediate. A mild copper-catalyzed cyclization of o/t/ o-haloanilides to give benzoxazoles 209 has been reported (Scheme 62) <2006JOC1802>. This route is conceptually different to the aforementioned methods in that the starting material is a 2-haloaniline rather than a 2-aminophenol. The reaction conditions tolerate various functional groups in the amide portion of the molecule. 

Amides and imides. The photochemical decarbo>ylation of acryloylojy-substituted long-chain carboxylic acids opens a path to macrocyclic lactams through radical photocyclization. Pyrrolyl and indolyl benzoxazoles have been obtained from the intramolecular O arylation in photostimulated reactions.The photocyclization of the... 

Direct Amination of Azoles, Decarbonylative amidation and amination of benzoxazole andbenzothiazole couldbe achieved using a Pd VAg system, promoted by carboxylic acid additives. Silver(I) fluoride performed inferiorly to Ag2C03 (30 vs. 78%). Stoichiometric amounts of silver salt were required to maximize reactivity no reaction occurred using only catalytic silver. Silver is postulated to help rearomatize the heteroarene following amination. Diversely substituted benzoxazoles and benzothiazoles afforded the C2-aminated product in moderate to excellent yield (eq 18). 

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