Mild Method for Ullmann Reaction of 2‐Chlorobenzoic Acids and Aminothiazoles or Aminobenzothiazoles under Ultrasonic Irradiation

Abstract

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1H and 13C spectral assignment of substituted 5H‐[1,3]thiazolo[2,3‐b]quinazolin‐5‐one and 12H‐[1,3]benzothiazolo[2,3‐b] quinazolin‐12‐one

“…The use of high power ultrasound enhanced yields and reduced the reaction time to minutes. [11] The simple 1 H NMR spectra at 300 MHz of compounds 1a-l and 2a-k are similar in the first aryl ring and the signal assigned to the benzene ring protons depending on the substituent present on this ring (Table 1 and 2). These substitutions have a little effect on chemical shift in the rest of the rings present in the molecules, although each one of the series is different.…”

Mechanistic Insight Leads to a Ligand Which Facilitates the Palladium‐Catalyzed Formation of 2‐(Hetero)Arylaminooxazoles and 4‐(Hetero)Arylaminothiazoles

“…The unsubstituted 5 H -oxazolo[2,3-b]quinazolin-5-one is previously unknown, although the thio-analog has been prepared using a copper catalyzed reaction. 15 …”

“…When using an aryl chloride bearing am ethyle ster group in the ortho position, condensationt ookp lace,t husr esultingi nt he formationo ft he tricyclic heterocycle 4j.A na ppreciabley ield waso btained with P3 in thep resence of NaOPh (Reaction conditions A).The unsubstituted5H-oxazolo[2,3-b]quinazolin-5-one was previously unknown, although the thio-analogue was prepared using ac opper-catalyzed reaction. [15] As 4-bromothiazole is also sensitive to strong base,amild homogeneous base was similarly expected to improve reaction outcomes with this coupling partner (Scheme 1). The precatalyst P3 (Reaction conditions A) afforded 5a and 5d in significantly higher yields with lower catalyst loadings than what was previously been reported.…”

Synthesis of new sulfonamide derivatives of thiazolo[3,2-a]quinazolin-5-one

“…Among known catalytic [7][8][9][10] and noncatalytic [11][12][13] synthetic approaches to the targeted heterocyclic system, the most interesting was that based on the condensation of substituted 2-halobenzoyl chlorides with 2-aminothiazole [14] (Scheme 1). This approach implies the use of a substrate containing an activated halogen substituent in the 2-position.…”