HETEROCYCLES

Review | Regular issue | Vol. 83, No. 12, 2011, pp. 2731-2767
Received, 21st September, 2011, Accepted, 24th October, 2011, Published online, 2nd November, 2011.
DOI: 10.3987/REV-11-717

■ Synthetic Access to Azolylthiazoles

Bakr F. Abdel-Wahab,* Hanan A. Mohamed, Abdelbasset A. Farahat, and Kamal M. Dawood

Applied Organic Chemistry Department, National Research Center, Dokki, Giza, Egypt

Abstract

Published data over the last years on the methods of synthesis and biological applications of azolylthiazoles are reviewed here for the first time till 2011. The review was classified according to the type of azole ring linked to thiazole.

1. INTRODUCTION
The linking of a thiazole ring with different azoles moieties by one single covalent bond give rise to a class of heterocyclic systems known as azolylthiazoles which have diverse biological activities. Bithiazole derivatives play an important role in the synthesis of polymers possessing magnetic properties,1 manufacture of high-performance electroluminescent devices such as light-emitting diodes,2 and medicine, for example, aminoalkyl derivatives of 2,4'-bithiazole-4-carboxylic acid were shown to exhibit antitumor activity.3 2',4-Disubstituted 2,4'-bithiazoles represent an important class of natural products which exhibit an intriguing and diversified spectrum of biological acitivities. Bleomycins4 and tallysomycins5 are glycopeptide antibiotics which carry a bithiazole amino acid at their C-terminal position. Another field of application of bithiazole derivatives includes synthesis of macrobicyclic cryptands.6 Despite of this versatile importance and in connection to our previous review articles about azolylthidiazoles7 and other heterocyclic systems,8-19 the azolylthiazoles has not previously reviewed. In this review, the azolylthiazoles systems have been classified according to the type of azole nucleus linked to thiazole.

2. PYRROLYLTHIAZOLES
Preparation of pyrrolylthiazoles as agrochemical fungicides has been reported. Thus, pyrrole-2-thioamides 1 were cyclocondensed with phenacylbromides 2 to give 2-(1H-pyrrol-2-yl)thiazoles 4 which gave complete control of Helminthosporium teres on barley plants when sprayed at 200 ppm and inhibited arachidonate-induced blood platelet aggregation in guinea pigs.20,21 While 2-(1,5-Dimethylpyrrol-2-yl)-5-phenyl-4-thiazolol 5 was synthesized by cyclocondensation of α-bromo carboxylate 3 with thioamides 1 (Scheme 1).22

The reaction of N-[2-(2-cyanoacetyl)hydrazinecarbonothioyl]benzamide 6 with phenacyl bromides 2 in boiling ethanol containing a catalytic amount of freshly fused sodium acetate afforded N-[3-(3-cyano-5-subst-2-oxo-2,3-dihydro-1H-pyrrol-1-yl)-4-methylthiazol-2(3H)-ylidene]benzamides 7 (Scheme 2).23

4-(2-Methyl-1H-pyrrol-3-yl)-2-(guanidino)thiazole 10 was prepared, as antiulcer agent, by condensation of (diaminomethy1ene)thiourea 8 with 2-chloro-1-(2-formyl-1H-pyrrol-4-y1)ethanone 9 (Scheme 3).24

2-Bromo-1-[5-methyl-1-(phenylsulfonyl)-1H-pyrrol-3-yl]ethanone 11 was cyclocondensed with thioamide in acetone followed by basification by refluxing in methanolic KOH to give 96% 2-[4-(5-methyl-1H-pyrrol-3-yl)thiazol-2-yl]guanidine 12 (Scheme 4).21

Diethyl 2,4-dibromo-3-oxoglutarate 14 was synthesized by bromination of diethyl 3-oxoglutarate 13 with of N-bromosuccinimide in carbon tetrachloride. The reaction of 14 with thiourea was carried out in ethanol at room temperature for 48 h and subsequent treatment with sodium carbonate furnished ethyl 2-(2-amino-5-ethoxycarbonylthiazol-4-yl)-2-bromoethanoate 15. Reacting 15 with 2,5-dimethoxy-tetrahydrofuran in acetic acid gave pyrrole derivative 16 (Scheme 5).25

YRAZOLYLTHIAZOLES
Pyrazolyl-1,3-thiazoles were prepared by different methods such as reaction of 2-bromoketones with carbothioamide or reaction of thiazolylhydrazines with dicarbonyl or 2-ketonitrile compounds.

3.1. Reaction between thiocarboxamides and 2-bromoketones
Pyrazole-1-carbothioamides 17 and phenacylbromides were refluxed in ethanol and acetic acid for 2 h to give 1-(thiazol-2-yl)-1H-pyrazoles 18 in good yields (Scheme 6).26-29

5-Hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-pyrazolethiocarboxyamides 19 were reacted with phenacylbromides, and 2-bromocyclohexanone 20 to give the corresponding pyrazolyl-thiazoles 23 and 25 after dehydration of 22 and 24 respectively (Scheme 7).30 The reaction of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one 21 with 5-hydroxy-3-methyl-5-(trifluoromethyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide 19 in chloroform under stirring for 24h at 35 °C furnished 27 after removing of water molecule from 26 (Scheme 7).31

Refluxing the appropriate α,β-unsaturated carbonyl compounds 28 with thiosemicarbazide in presence of NaOH provided the requisite 29 in good overall yields. Reactions of 29 with 2,3-dichloroquinoxaline, substituted phenacyl bromides, and chloroacetic acid and aromatic aldehydes, afforded the corresponding 3,5-diaryl-1-(thiazolo[4,5-b]quinoxalin-2-yl)-2-pyrazoline derivatives 30; 3,5-diaryl-1-(4-aryl-2-thiazolyl)-2-pyrazolines 31; 3,5-diaryl-1-(5-arylidene-4,5-dihydro-4-oxo-2-thiazolyl)-2-pyrazolines 32 (Scheme 8).32-35

7-Benzylidene-3,3a,4,5,6,7-hexahydro-3-phenyl-2-thiocarbamoyl-2H-indazole 34 was synthesized by the reaction of 2,6-bis-benzylidenecyclohexanone 33 with thiosemicarbazide in presence of NaOH. Reaction of 34 with 2,3-dichloroquinoxaline, substituted phenacyl bromides in absolute ethanol, and aromatic aldehydes and chloroacetic acid in presence of a mixture of acetic acid and acetic anhydride gave the corresponding fused 7-benzylidene-3,3a,4,5,6,7-hexahydro-3-phenyl-2-(thiazolo[4,5-b]-quinoxalin-2-yl)-2H-indazole 35, 2-(4-aryl-2-thiazolyl)-7-benzylidene-3,3a,4,5,6,7-hexahydro-3-phenyl-2H-indazole analogues 36 and 2-(5-arylidene-4,5-dihydro-4-oxo-2-thiazolyl)-7-benzylidene-3,3a,4,5,6,7-hexahydro-3-phenyl-2H-indazole derivatives 37 (Scheme 9).33

Reaction of 3-(bromoacetyl)coumarins 38 with thiosemicarbazide and acetylacetone gave 3-[2-(3,5-dimethyl-1H-pyrazol-1-yl)thiazol-4-yl]-2H-1-benzopyran-2-ones 39 and a in 72-90% yield under solvent free conditions (Scheme 10).36

he antiinflammatoric 1-phenylpyrazolyl-4-heteroarylalkanoic acids 41 have been prepared from pyrazoles 40 and 3-amino-3-thioxopropanoic acid (Scheme 11).37

3.2. Reaction of hydrazines with β-diketones
Regioselectivity of the synthesis of 2-pyrazolinylthiazoles by reacting 2-hydrazinothiazoles with unsymmetrical β-diketones was reported. 2-Pyrazolinylthiazoles 44 were prepared regioselectively by cyclocondensation of 4-substituted-2-hydrazinothiazoles 42 with 1,3-dicarbonyl compounds 43. The aromatization of 44 via dehydration to give 2-(3-aryl-5-trifluoromethylpyrazol-l-yl)thiazoles 45 (Scheme 12) required forcing conditions (boiling acetic anhydride).38

Reaction of 2-hydrazinothiazoles 42 with 1-thienyl- and 1-furyl-1,3-butanediones 46 in methanol in the presence of hydrochloric acid mainly led to a mixture of pyrazoles and pyrazolines 49-52 in strong acidic conditions. Isomeric hydrazones and pyrazolines 47-50 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones with 2-hydrazinothiazoles is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones. Cyclization of hydrazones is shown to occur under milder conditions than dehydration for pyrazolines 49 and 50 (Scheme 13).39

The pyrazolylthiazoles 54 were prepared by the condensation of appropriate 2-hydrazino-4-arylthiazoles 42 with β-diketones 53 (Scheme 14).40-44

However, treatment of 2-hydrazino-4-(2-thienyl)thiazole 42 with 2-formylcyclohexanone yielded 55 as major product. Which could be obtained exclusively by the reaction of tetrahydroindazolyl-1-thiocarboxamide 56 and phenacyl bromides (Scheme 15).43

3.3. Reaction with β-keto-nitriles
Condensation of 2-hydrazinothiazole 42 and 4-aroylaceteonitriles 57 gave 52-73% pyrazolylthiazoles 58 (Scheme 16).26

Thiazolinonylpyrazoles 60 were synthesized via the reactions of 2-α-cyanoacetonyl-2-thiazolin-4-one 59 with hydrazine derivatives (Scheme 17).45

4. IMIDAZOLYLTHIAZOLES
Microwave-assisted synthesis of a novel class of imidazolylthiazolidin-4-ones has reported. Thus, generation of imidazolylthiazolidin-4-ones achieved 64, in two steps, by reacting a mixture of 5-phenyl-1H-imidazol-2-amine 61, 2,5-disubs. benzaldehyde 62 in dry toluene using 5 mol% of Yb(OTf)3 as catalyst, followed by reaction with mercaptoacetic acid under microwave irradiation (Scheme 18).46

Ring closure of arylthioureas 65 with ethyl bromoacetate followed by chlorination of the resulting 2-phenylaminothiazol-4-ones 66 with phosphorus oxychloride yielded (4-chlorothiazol-2-yl)phenylamines 67 as intermediates. The desired [4-(imidazol-1-yl)- thiazol-2-yl]phenylamines 68 were obtained by nucleophilic aromatic substitution in DMF solution, using the respective imidazoles in excess as reagents and bases which used as potent Colchicine site binding Tubulin inhibitors (Scheme 19).47

4-(4-Methyl-5-imidazolyl)thiazole 70 was prepared by reaction of 4-methyl-5-bromoacetylimidazole 69 with thiourea (Scheme 20).48

5. Thiazolyloxazoles
Agrochemical microbicides contain thiazolyloxazoles 74 prepared by treatment of α-furyl-aminoacetonitrile 72 in ethyl acetate/triethylamine with 2,4-dimethylthiazole-5-carboxylic acid chloride 71 at room temperature to give 73 which in ethanol was treated with benzaldehyde in the presence of piperazine at 60 °C for 2 h to afford 74 (Scheme 21).49

Upon reacting thiazole 75 with 2-trimethylsilyl-1,2,3-triazole 76 in refluxing toluene for three days gave thiazolyl oxazole 78 in a 86% yield by nitrogen elimination rearrangement reaction of the triazole amide 77 (Scheme 22).50

Reaction of 2-aryloxazole-4-carboxylic acid thioamides 79 with different phenacylbromides gave 4-(thiazol-2-yl)oxazoles 80 in high yield (Scheme 23).51

3-(5-Nitro-2-thiazolyl)-2-oxazolidinone 82 was obtained by refluxing 2-chloroethyl 5-nitrothiazol-2-ylcarbamate 81 in DMF with sodium hydride and ethanol at pH 5 (Scheme 24).52-54

The synthesis of a directly connected thiazole-oxazole ring system 90 present in Microcin B17 was reported. Aminoacetonitrile hydrochloride 83 was converted to 84 under standard benzoylation conditions. Hydrogen sulfide treatment of an aqueous ethanolic ammonia solution of 84 provided the thioamide 85, which on condensation with ethyl bromopyruvate in boiling methanol afforded the fully protected thiazole amino acid 86. Selective hydrolysis of the ester group provided 87, which the coupling of 87 with DL-serine methyl ester 88 preceded under standard solution to afford 2-(benzamidomethyl)-4-{N-[1-(methoxycarbonyl)-2-hydroxyethyl]carbamoyl}thiazole 89 which undergo cyclization using Burgess reagent {methyl N-[(triethylammonio)sulfonyl]carbamate}, the aromatization of dihydroxazole 90 was performed using CuBr2-DBU system to afford 91 (Scheme 25).55

6. BITHIAZOLES
6.1. 2,2'-BITHIAZOLES
2,2'-Bithiazole 93 has been synthesized in good yield via homocoupling of 2-bromothiazole 92 in the presence of a catalyst such as Pd(OAc)2/LiCl (72% yield)56; Pd(OAc)2/n-Bu4NBr/iPr2EtN (86% yield)56; Pd(PPh3)4/Bu3SnSnBu3 (79% yield)57; BuLi/CuCl (52% yield)58 (Scheme 26). Also, 2,2'-bithiazole 93 was prepared by decarboxylation of ethyl 2-(thiazol-2-yl)thiazole-3(2H)-carboxylate 94 using o-chloranil (Scheme 26).59

Bithiazoles 96 were prepared in 80-90% yield by cyclocondensation of 1 mole rubeanic acid 95 with 2 moles appropriate α-bromo ketone.60-66 4,4'-Bis(chloromethy1)-2,2'-bi-1,3-thiazole 97 was prepared by condensation of 95 and 1,3-dichloroacetone.67,68 5,5'-Bis(2,5-dihydroxy-3,4,6-trichlorophenyl)-2,2'-bithiazole 99 was synthesized from 2,5-dihydroxy-3,4,6,7-tetrachloro-2,3-dihydrobenzo[b]furan 98 and dithiooxalyl diamide 95.69 2,2'-Bithiazolines 101 were prepared by reaction of 2-amino-alcohol derivatives 100 with ethanebis(thioamide) 95 in two steps (Scheme 27).64,70

Condensation of 2-(4-bromo-3-oxobutan-2-yl)isoindoline-1,3-dione 102 and 2-(5-bromo-4-oxopentan-2-yl)isoindoline-1,3-dione 103 with ethanebis(thioamide) 95 in ethanol gave the corresponding 4,4'-bis(1,2-phthalimidoethyl)-2,2'-bithiazole 104 and 4,4'-bis(2-phthalimidopropyl)-2,2'-bithiazole 106 in good yields, hydrolyzed to the di-HCl salts of 4,4'-bis(1-aminoethyl)-2,2'-bithiazole 105 and 4,4'-bis(2-aminopropyl)-2,2'-bithiazole 107 (Scheme 28).71

Refluxing 2-thiocarbamylthiazoles 108 with 2-bromoacetaldehyde in dioxane gave 5-acetyl-2,2'-bithiazole 109. Condensation of 2-thiocarbamylthiazoles 108 with the appropriate bromoketone by refluxing in glacial AcOH or dioxane and purification gave 5-acetamido-4'-alkyl-2,2'-bithiazoles 110 (Scheme 29).72,73

4-(2-Thienyl)thiazole-2-thiocarboxamide 111 on treatment with a variety of α-tosyloxy ketones afforded 4-substituted 4'-(2-thienyl)-2,2'-bithiazoles 112.74 Condensation of 111 with phenacyl bromides gives 4-aryl-4'-(2-thienyl)-2,2'-bithiazoles 112. Compounds 112 show varying degrees of phototoxicity when tested against mosquito larvae (Scheme 30).75

The organo-zinc intermediate 113 was converted to bithazole 114, 2,2'-bithiazole 115, 2,2'-dichloro-5,5'-bithiazole 116 by treatment with 2-bromothiazole, in the presence of Pd(PPh3)4, and under microwave conditions (Scheme 31).76

6.2. 2,4'-BITHIAZOLES
2'-Substituted 4-bromo-2,4'-bithiazoles were prepared from 2,4-dibromothiazole by regioselective cross-coupling reactions. Cross-coupling of an organometallic reagent with 2,4-dibromothiazole 117 should occur at the 2-position. Subsequent bromo-lithium exchange generates a carbon nucleophile that can react in a second step with another molecule of compound 117 to the desired product 118. The Negishi cross-coupling gave high yields of the 2'-alkyl-4-bromo-2,4'-bithiazoles 118 (88-97%). The synthesis of the 2'-phenyl- and 2'-alkynyl-4-bromo-2,4'-bithiazoles 118 required a Stille cross-coupling that did not proceed as smoothly as the Negishi cross-coupling (58-62% yield) (Scheme 32).77

2,4'-Bithiazoles 121 was prepared in 95% yield by treatment of 119 With 2-(trimethylstannyl)thiazole 120 (Scheme 33).78

2,4'-Bithiazoles 124 obtained by cyclization of thioacetamides 123 with 2-bromo-1-(4-subst-thiazol-2-yl)-ethanone 122 (Scheme 34).79-83

Hantzsch cyclization of 125 with ethyl bromopyruvate was performed in the presence of 1,2-epoxybutane to trap HBr as it evolved during cyclization. The crude hydroxylated intermediate was then dehydrated with trifluoroacetic anhydride in pyridine at _20 °C to afford monochlorobithiazole ethyl ester 126 in 70% yield (Scheme 35).73

Bithiazoles 130 were prepared, in 50-90% yield, by reaction of thioamides 127 with α-haloketones 128 in acetone. Treatment of 130 with 98% sulfuric acid gave 2,4-bithiazole 131 in 80-95% yield, while on treatment with acetic anhydride furnished 5-acetylbithiazoles 132 (Scheme 36).84

The synthesis of 2'-phenyl-5'-bromo-4-chloromethyl-2,4'-bisthiazole 137 starting from the oxime of 2-phenyl-4-formylthiazole 133 has been reported, thus, bromination of the oxime 133 followed by dehydration afforded 5-bromo-2-phenylthiazole-4-carbonitrile 135. Thiohydrolysis of the latter gave 5-bromo-2-phenylthiazole-4-carbothioamide 136 which on treatment with 1,3-dichloropropan-2-one led to the target compound 137 (Scheme 37).85

6.3. 2,5'-BITHIAZOLES
The 2,4-diaminothiazole-5-carbothioamides 138 react with halomethyl carbonyl compounds 139 and Mg(ClO4)2 in Ac2O, the corresponding 2',4'-bis(dialkylamino)-3,4-diaryl[2,5'-bithiazol]-3-ium perchlorates 141 and 142 were isolated (Scheme 38). These compounds result, obviously, via the primarily formed 140 by a ring-closure reaction between the carbonyl and iminium groups (Scheme 38).86

Halothiazoles 143 were submitted to the cross-coupling conditions with least-reactive 4-bromothiazole gave 36% of the cross-coupling product 144. A similar result was obtained when 2-bromo-5-iodothiazole. In the reaction with 2-bromothiazole, 2'-chloro-2,5'-bithiazole 145 was obtained. Finally, 2,4-dibromo-thiazole was cross-coupled to 143 to afford 4-bromo-2'-chloro-2,5'-bithiazole 146 (Scheme 39).76

6.4. 4,4'-BITHIAZOLES
1,4-Dibromobutane-2,3-dione 147 was treated with triethyl orthoformate and the resulting 1,4-dibromo-3,3-diethoxybutan-2-one 148 cyclized with thiourea derivative 149 to give 2-guanidino-4-(2-bromo-1,1-diethoxyethyl)thiazole 150, which was hydrolyzed with HBr followed by cyclization with thiourea to give 1-(2'-amino-4,4'-bithiazol-2-yl)guanidine.2HBr 151 (Scheme 40).87

Heating of the dibromoketones 153 with thioamides 152 gave 2,2'-disubst-5,5'-dimethyl-4,4'-bithiazole-HBr 154 in high yields.7,36,37 On the other hand, the bithiazoles 155 was prepared by cyclization of the thiazoles 122 with thiocarboxamide 152 (Scheme 41).80

External irradiation of methyl 2'-methyl-2,4'-bithiazole-4-carboxylate 156 in acetonitrile with a 60 W transilluminator (302 nm) gave 4,4'-bithiazole 157 in 95% yield as determined by HPLC. A more careful examination of the photolysate revealed the presence of another isomer 158 in 2% yield (Scheme 42).88

Al-Azawe in 1988 reported the synthesis of 4,4'-bithiazoles 161 by treatment of pridylthiazoles 159 with Grignard reagents 160 (Scheme 43).89

2,2'-Diamino-4,4'-bithiazole 162 was nitrated or acylated and then nitrated to obtain 2,2'-diamino-5,5'-dinitro-4,4'-bithiazole (163, X = NO2, R= H) and 2,2'-diamino-diacetylamino-4,4'-bithiazole (163, X = Ac, R= H) and 2,2'-diacetylamino-5,5'-dinitro-4,4'-bithiazole (163, X = NO2, R= Ac) (Scheme 44).90

6.5. 4,5'-BITHIAZOLES
2'-Chloro-4,5'-bithiazoles (164, X= H) and 5-bromo-2'-chloro-2,5'-bithiazoles (164, X= Br) were obtained by cross-coupling of 2-bromothiazole derivatives with 2-chlorothiazoles 143 (Scheme 45).76

The bithiazoles 166, which have antiinflammatory activities, were prepared by cyclization of 165 with thioamides 152 (Scheme 46).91

Heating of 3-dimethylamino(thiopropanamide) hydrochloride 167 and 5-bromoacetyl-2,4-dimethylthiazole hydrobromide 168 in ethanol for 2h followed by basification gave 2-(2'',4''-dimethyl-4',5''-bithiazol-2'-yl)-N,N-dimethylamine 169 in 60% yield (Scheme 47).83

The preparation of bithiazole 175 was accomplished by condensation of chlorodiketone 170 with N-pivaloylcarbamimidothioic acid 171 to give 1-(thiazol-5-yl)ethanone intermediate 172. α-Bromination of the later to the carbonyl of 173 and subsequent condensation with N-(5-chloro-2-methoxyphenyl)carbamimidothioic acid 174 delivers 175 ( Scheme 48).92

1-(2-Amino-4-ethylthiazol-5-yl)propan-1-one 177 was prepared in 80% yield by bromination of 3,5-heptanedione 176 in ethanol solution followed by addition of thiourea. Bromination of 177 in acetic acid led to 1-(2-amino-4-ethylthiazol-5-yl)-2-bromopropan-1-one 178 in 86% yield. Reaction of 178 with 179 gave 4-(2-amino-4-ethylthiazol-5-yl)-N-(5-chloro-2-methoxyphenyl)-5-methylthiazol-2-amine 180 in 99% yield. N-(5-(2-(5-Chloro-2-methoxyphenylamino)-5-methylthiazol-4-yl)-4-ethylthiazol-2-yl)-pivalamide 181 was obtained in 66% yield by reaction of a suspension of 180 in DCM and TEA with pivaloyl chloride (Scheme 49).92

The reaction of 5-bromo-2,4-dimethylthiazole 182 with thioacetamide and N-methylthiourea gave 2,2',4'-trimethyl-4,5'-bithiazole 183 and the corresponding amine 184 respectively (Scheme 50).93

N-Allyl-N-[5-(3-allyl-2-oxothiazolidin-4-ylidene)-4-oxo-4,5-dihydrothiazol-2-yl]acetamide 186 was prepared in 35% yield by heating of 2-(allylamino)thiazol-4(5H)-one 185 in a mixture of acetic anhydride and acetic acid (2:1 v/v) at 140 °C. Alternative synthesis of 186 in 53% yield was occurred by reaction of N-allyl-N-(4-oxo-4,5-dihydrothiazol-2-yl)acetamide 187 with 3-allylthiazolidine-2,4-dione 188 (Scheme 51).94

N-[tert-Butoxycarbonyl (Boc)] protected alkylenediamine-N-propionthioamides 190 were obtained by thiation of the amido carbonyl groups in 189 with 2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide (Lawesson’s reagent) in 70 and 61% yields using dry 1,2-dimethoxyethane (DME) as reaction solvent. When two equimolar amounts of 190 were reacted with 1,4-dibromobutane-2,3-dione at 70 °C for 2 h to provide the corresponding 4,4'-bithiazoles, 2,2'-bis[3,6,9-tri(Boc)-3,6,9-triazanonyl]- and 2,2'-bis[3,7,11-tri(Boc)-3,7,11-triazaundecyl]-4,4'-bithiazoles 191 in 73% and 60% yields respectively. Acidic deprotection of the amino groups in 191 afforded the bithiazoles 192 that were useful to inhibit the DNA cleavage (Scheme 52).95

6.6. 5,5'-BITHIAZOLES
5,5'-Bithiazole 193 was prepared in 75% yield by treatment of 5-bromothiazole with 5-(trimethylstannyl)thiazole (Scheme 53).78

2,2'-Diphthalimido-5,5'-bithiazole 196 was prepared in 20% yield by reaction 2,2'-hydrazobisthiazole-2HCl 194 with phthalic anhydride 195 (Scheme 54).96

Bithiazole derivatives are prepared by coupling reaction of thiazole derivatives. Thus, a mixture of 2-(4-methoxyphenyl)thiazole 197, PdCl2(PhCN)2, and DMSO was treated with AgF at 60 °C for 5 h to give 52,2'-bis(4-methoxyphenyl)-5,5'-bithiazole 198 in 83% yield (Scheme 55).97

7. THIAZOLYLISOXAZOLES
The product of Claisen Schmidt condensation of 5-acetyl-2-arylamino-4-methylthiazoles 199 reacted with hydroxyl amine to give and thiazolylisoxazolines 201. Some 201 were screened for fungicidal activity against Penicillium notatum (Scheme 56).98,99

1,3-Dicarbonyl compounds with a 5-nitro-2-thiazolyl moiety 202 reacted with substituted hydrazines or hydroxylamine to give 26-96% the title pyrazoles (203, 204 X = NH) or isoxazoles (203, 204 X = O). Some 203 have good antimicrobial activity (Scheme 57).100

The hydroxamoyl chlorides 205 react with acetylenes 206 and alkene 207 dipolarophiles to give regioselective 3-thiazolylisoxazoles 208 and 3-thiazolylisoxazolines 209 in moderate to good yields (Scheme 58).101

8. TRIAZOLYLTHIAZOLES
3-(1,2,4-Triazol-3-yl)-4-thiazolidinone derivatives 211, showed antibacterial and antifungal activities, have been synthesized by the reaction of Schiff bases of 3-amino-1,2,4-triazoles 210 with mercaptoacetic acid and 2-mercaptopropionic acid (Scheme 59).102,103

Also, 3-(5'-aryl-3'-mercapto-1',2',4'-triazol-4'-yl)-2-aryl-4-thiazolidinones 213 were prepared by the cyclocondensation of mercaptoacetic acid and anils 212 (Scheme 60).104

3-(1,2,4-Triazol-3-yl)-4-thiazolidinone derivatives 215 has been synthesized by the reaction of Schiff bases of 3-amino-1,2,4-triazoles 214 with mercaptoacetic acid and 2-mercaptopropionic acid (Scheme 61).102

1-(2,4-Dichlorophenyl)-3-[4-aryl-5-(1H-1,2,4-triazol-1-yl)thiazol-2-yl]urea derivatives 217 were synthesized by the reaction of 2-amino-4-(substituted phenyl)-5-(1H-1,2,4-triazol-1-yl)thiazoles 216 with 2,4-dichloro-1-isocyanatobenzene, the structure was confirmed by single crystal X-ray diffraction (Scheme 62).105

3-(5'-Aryl-3'-mercapto-1',2',4'-triazol-4'-yl)-2-aryl-4-thiazolidinones 219, have insecticidal activities, were prepared by cyclization of 218 with mercaptoacetic acid (Scheme 63).104,106,107

Reaction of hydrazide 220 with phenyl isothiocyanate in ethanol and aqueous sodium hydroxide at room temperature gave compound 221. Refluxing the latter compound with aqueous sodium bicarbonate afforded 4-alkyl(or phenyl)-5-(2,4-dimethyl-5-thiazolyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione 222 (Scheme 64).108,109

Compounds 224 were synthesized from the reaction of α-bromo-substituted acetophenones 223 and thiourea by the Hantzsh reaction (Scheme 65).110

Reaction of 1,2,4-triazol-4-amine 225 with arylisothiocyanates gave thioureas 226 which underwent cyclization with 1,2-dibromoethane in the presence of potassium carbonate to afford 1,2,4-triazol-4-ylthiazolidones 227 (Scheme 66).111

Reacting of 4-isopropylthiazole-2-carbahydrazide 228, with carbon disulfide under strong basic conditions followed by cyclization with hydrazine hydrate yielded 4-amino-5-(4-isopropyl-1,3-thiazol-2-yl)-4H-1,2,4-triazole-3-thiol 229 (Scheme 67).112

1-(4-Aryl-5-triazolyl-2-thiazolyl)-3,5-diaryl-2-pyrazolines 232 were synthesized by reacting 3,5-diaryl-1-thiocarbamoyl-2-pyrazolines 230 with 2-bromo-1-aryl-2-(1H-1,2,4-triazol-1-yl)ethanones 231 in boiling ethanol (Scheme 68).113

9. THIAZOLYLOXADIAZOLES
2-(2-Adamant-1-yl-1,3-thiazol-4-yl)-5-aryl-1,3,4-oxadiazoles 237 was synthesized from adamantane-1-nitrile 233 in 4 steps. Adamantan-1-nitrile 233 was converted into thioamide 234 (52%), using P4S10 followed by its treatment with ethyl bromopyruvate to afford 235 (80%). Hydrazinolysis of 235 gave the carbohydrazide-1,3-thiazole 236 in 75% yield. Heating 236 with substituted benzoic acids in the presence of polyphosphoric acid (PPA) furnished 1,3,4-oxadiazole derivatives 237 in 61-66% yields (Scheme 69).114

10. THIAZOLYTHIADIAZOLES
(Thiazolecarbonyl)thiosemicarbazides 238 were prepared and converted to thiadiazoles 241, which exhibited fungicidal activity, by treatment with sulfuric acid (Scheme 70).115

Stirring 2,4-dimethylthiazol-5-carbohydrazide 242 in ethanol and 85% potassium hydroxide for 30 min followed by addition of carbon disulphide gave potassium dithiocarbazate 243 which under ring closure gave 5-(2',4'-dimethylthiazole-5yl)-1,3,4-thiadiazole-2(3H)-thione 244 with 54% yield (Scheme 71).83

11. TETRAZOLYLTHIAZOLES
Diarylthiazolotriazoles 246 were prepared by thermolysis of aryltetrazoles 245 (Scheme 72).116

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