TBHP/AIBN-Mediated Synthesis of 2-Amino-thioazoles from Active Methylene Ketones and Thiourea under Metal-free Conditions

An Overview of Recent Developments in the Synthesis of Substituted Thiazoles

“…Sun et al . developed the preparation of 2‐amino thiazoles ( 172 ) from α ‐substituted ketone compounds ( 171 ) and thiourea ( 121 ).…”

“…The successful recovery of brominating agent and its subsequent use highlights the greener aspects of the protocol (Scheme 57). Sun et al [71] developed the preparation of 2-amino thiazoles (172) from α-substituted ketone compounds (171) and thiourea (121). The electron-releasing groups affect the reaction negatively, but the electron-withdrawing groups delivered the product 172 in satisfactory to high yields (Scheme 58).…”

Facile one-pot synthesis of thiazol-2(3H)-imine derivatives from α-active methylene ketones.

“…Several methods for the synthesis of thiazoles and their derivatives were developed by various catalysts, conditions, and strategies [12][13][14][15][16][17][18][19][20][21]. From these methods, we were interested in the synthesis of thiazoles by condensation of α-halo ketones with thioamides [22][23][24][25][26][27][28]. Beyzaei et al reported the one-pot synthesis of thiazol-2(3H)-imines through nucleophilic substitution of chloride in 3chloroacetylacetone with thiocyanate group followed by cyclo condensation with various hydrazine or hydrazide derivatives.…”

One‐Pot Preparation of Aromatic Amides, 4‐Arylthiazoles, and 4‐Arylimidazoles from Arenes

“…NH 3 at 60 °C (the Wohl‐Ziegler‐type and Lieben iodoform‐type reactions);[9e] and using aryl bromides, Co 2 (CO) 4 , and NH 4 Cl in the presence of Pd(OAc) 2 and dppf as catalysts at 90 °C (aminocarbonylation)[9f] was reported. Regarding recent synthetic studies of thiazoles and imidazoles, the preparation of thiazoles from the reaction of active methylene ketones with thiourea, TBHP, and 2,2′‐azobis(isobutyronitrile) (AIBN) in methanol at room temperature;[10a] the reaction of 4‐bromo‐3‐ethoxycrotonate with thioamides in 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) under refluxing conditions,[10b] the reaction of α‐nitroepoxides with S ‐alkyl dithiocarbamates at 60 °C without solvent,[10c] the reaction of oximes with carboxylic anhydrides, KSCN, and CuI in toluene at 120 °C;[10d] the reaction of terminal alkynes with sulfonyl azides, thionoesters, and Rh 2 (O 2 CBu t ) 4 in CHCl 3 at 70 °C;[10e] the reaction of arylacetylenes, thiourea, and NBS in water at 70 °C;[10f] the reaction of α‐diazoketones with thioamides and Rh 2 (NHCOC 3 F 7 ) 4 in toluene under microwave irradiation;[10g] the reaction of methyl ketones with thiourea, molecular iodine, and CuO in ethanol at 78 °C;[10h] and the reaction of polymer‐supported thiourea with α‐haloketones in DMF at 70 °C[10i] was reported. The preparation of imidazoles from the reaction of benzylic primary amines with nitriles and t BuOK in toluene at 130 °C;[11a] the reaction of tertiary α‐aminoamides with Tf 2 O in nitrile at 0 °C;[11b] the reaction of methyl ketones with anilines, p ‐tosylmethyl isocyanide, and molecular iodine in DMSO at 110 °C;[11c] the reaction of α‐amino acid esters with α‐ketoaldehydes and SeO 2 in acetonitrile at room temperature;[11d] the reaction of arylacetylenes with arenesulfonyl azides, CuTC, BrCN, and Rh 2 (esp) 2 in benzene at 70 °C;[11e] and the reaction of α‐tosyloxyketones with amidines in water at 60 °C[11f] was reported.…”

“…The preparation of imidazoles from the reaction of benzylic primary amines with nitriles and t BuOK in toluene at 130 °C;[11a] the reaction of tertiary α‐aminoamides with Tf 2 O in nitrile at 0 °C;[11b] the reaction of methyl ketones with anilines, p ‐tosylmethyl isocyanide, and molecular iodine in DMSO at 110 °C;[11c] the reaction of α‐amino acid esters with α‐ketoaldehydes and SeO 2 in acetonitrile at room temperature;[11d] the reaction of arylacetylenes with arenesulfonyl azides, CuTC, BrCN, and Rh 2 (esp) 2 in benzene at 70 °C;[11e] and the reaction of α‐tosyloxyketones with amidines in water at 60 °C[11f] was reported. Among the many methods for the preparation of primary aromatic amides, thiazoles, and imidazoles, including those mentioned above, the Lieben iodoform‐type reaction for the preparation of primary aromatic amides from aryl methyl ketones[9c], [9e], and the Hantzsch reaction for the preparation of thiazoles and imidazoles from α‐haloketones with thioamides and amidines[10h], [10i], [11f], are some one of the most useful and conventional ones and have sufficient potential for application to a wide range of substrates. Here, we would like to report an easy preparation of primary aromatic amides, 4‐arylthiazoles, and 4‐arylimidazoles from arenes via aryl α‐bromomethyl ketones with α‐bromoacetyl chloride and AlCl 3 using the Friedel–Crafts acylation, followed by the treatment with molecular iodine and aq.…”