Synthesis of novel heterocycles : Oxazolo[4,5-b]pyridines and oxazolo[4,5-d]pyrimidines

Silica Supported Fluoroboric Acid: An Efficient and Reusable Heterogeneous Catalyst for Facile Synthesis of 2-Aliphatic Benzothiazoles, Benzoxazoles, Benzimidazoles and Imidazo[4,5-b]pyridines

“…1 H NMR spectra were recorded using a JEOL FT-NMR (400 MHz) spectrometer using TMS as an internal standard. The structures of all the products were confirmed by 13 C NMR, 1 H NMR and IR data and comparison with authentic samples prepared according to the literature methods.…”

“…1,2 These heterocycles have achieved significance in pharmacology as antibacterial, 3 antiviral, 4 antifungal, 5 anticancer, 6 anticonvulsant 7 and immunosuppressant agents. 8 Quite a plethora of methods have been developed for the preparation of these heterocycles including the condensation of carboxylic acids, 9 acid chlorides, 10,11 orthoesters, [12][13][14] esters, 15 and aldehydes [16][17][18][19][20][21] with o-aminophenols, o-aminothiophenols and o-phenylenediamines, dehydration of o-acylaminophenols, 22 the reaction of o-quinones with amines 23 and Beckmann rearrangement of o-acylphenoloximes. 24 However all of these procedures suffer from one or more of the following drawbacks such as long reaction time, low yield of the products, harsh reaction conditions, use of excess amount of reagents, tedious work up procedures and co-occurrence of several side reactions.…”

Sonicated Assisted Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles in Aqueous Media

“…The reaction mixture was sonicated at room temperature (25 0 C) for the appropriate time ( Table 2, entries [13][14][15][16][17][18][19][20][21][22][23][24][25], and the progress of reaction was monitored by TLC. After completion of reaction, the mixture was extracted with ethyl acetate (2×10mL).…”

“…These heterocycles shows different pharmacological properties such as antibacterial 6 , antiviral 7 , antifugal 8 , anticancer 9 , anticonvulsant 10 and immunosuppressant 11 . These heterocycles can be prepared by condensing carboxylic acid 12 , acid chloride 13,14 , orthoester [15][16][17] , esters 18 and aldehydes [19][20][21][22][23][24] with o-phenylenediamine, o-aminophenols and o-aminothaiophenols, dehydration of o-acylaminophenols 25 , reaction of o-quinones with amines 26 and Beckmann rearrangement of o-acylphenoloximes 27 . The most common method of synthesis of these heterocycles includes condensation of o-phenylenediamine, o-aminophenol or o-aminothiophenol with suitable aldehyde [28][29][30][31][32] .…”

One pot synthesis of benzoxazoles, benzthiazoles and benzimidazoles from carboxylic acids using ionic liquid

“…A number of methods have been reported for the synthesis of these heterocycles which include condensation of carboxylic acids 13 and their derivatives like orthoesters, [14][15][16] nitriles, 17 amides, 18 aldehydes 19 and esters 20 with osubstituted aminoaromatics. Beckmann rearrangement of o-acylphenol oximes 21 and photocyclization of phenolic Schiff bases also produce these componds 22 .…”