Palladium-catalyzed Ligand-directed Acylation And Chlorination Of Ortho-C-H Bond

The acylation of2-arylbenzoxazoles with alkyl aldehydes or arylmethyl alcohols as the acylation reagent was carried out; the ortho-acylation of2-aryl pyridines with the arylmethyl amines as acylation reagents was also expored; the ortho-chlorination of2-arylpyridines has been investrigated using DDQ as the dual roles of the chlorinating reagent and oxidant.1The acylation of2-arylbenzoxazoles with aldehydes as the easily accessible acyl source was performed in chlorobenzene in the presence of tert-butyl hydroperoxide (TBHP) as the oxidant, affording the acylated products in mostly moderate to good yields (Scheme1). The acylation exhibited high regioselectivity for the substrates containing a meta-substituent in the benzene ring and typically occurred at the less sterically hindered ortho-C-H bond of the directing group, which was unambiguously determined by the single crystal X-ray diffraction study. All the new compounds were characterized by1H NMR,13C NMR and HR-MS.2A facile and efficient protocol for the synthesis of the acylated2-arylbenzoxazoles and2-arylbenzothiazoles by heterocycle-directed ortho-acylation was developed. This reaction was performed in chlorobenzene, using arylmethyl alcohols and tert-butyl hydroperoxide (TBHP) as the easily accessible acyl source and the oxidant, respectively, affording the desired products in mostly moderate to good yields (Scheme2). The acylation exhibited high regioselectivity, and all the new compounds were characterized by1H NMR,13C NMR and HR-MS.3A facile and efficient protocol for palladium-catalyzed ortho-acylation of2-aryl pyridines with arylmethyl amines in chlorobenzene using tert-butyl hydroperoxide (TBHP) as the oxidant was developed (Scheme3). Note that the arylmethyl amines were used as new, cheap and readily available acylation reagents, and the ortho-acylation of C-H bond showed high regioselectivity. The catalytic system could tolerate various functional groups, affording the desired products in mostly moderate to good yields.4A new and simple protocol for palladium-catalyzed ligand-directed ortho-chlorination of2-arylpyridines with DDQ was developed, generating the chlorinated products in good to excellent yields (Scheme4). Note that DDQ behaved dual roles as both the chlorinating reagent and oxidant in this reaction. Moreover, high regioselectivity was observed for2-arylpyridines bearing a meta-substituent in the aryl ring moiety, and the chlorination could take place at less sterically hindered ortho-C-H bond.