Synthesis of Some New 2‐Oxo‐N‐[(10H‐phenothiazin‐10‐yl)alkyl] Derivatives of Azetidine‐1‐carboxamides

The synthesis of a new series of 4‐aryl‐3‐chloro‐2‐oxo‐N‐[3‐(10H‐phenothiazin‐10‐yl)propyl]azetidine‐1‐carboxamides, 4a – 4m , is described. Phenothiazine on reaction with Cl(CH₂)₃Br at room temperature gave 10‐(3‐chloropropyl)‐10H‐phenothiazine ( 1 ), and the latter reacted with urea to yield 1‐[3‐(10H‐phenothiazin‐10‐yl)propyl]urea ( 2 ). Further reaction of 2 with several substituted aromatic aldehydes led to N‐(arylmethylidene)‐N′‐[3‐(phenothiazin‐10‐yl)propyl]ureas 3a – 3m , which, on treatment with ClCH₂COCl in the presence of Et₃N, furnished the desired racemic trans‐2‐oxoazetidin‐1‐carboxamide derivatives 4a – 4m . The structures of all new compounds were confirmed by IR, and ¹H‐ and ¹³C‐NMR spectroscopy, FAB mass spectrometry, and chemical methods.     

Cationic,water‐soluble,fluorene‐containing poly(arylene ethynylene)s: Effects of water solubility on aggregation,photoluminescence efficiency,and amplified fluorescence quenching in aqueous solutions

Three novel fluorene‐containing poly(arylene ethynylene)s with amino‐functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐{2,5‐bis[3′‐(N,N‐diethylamino)‐1′‐oxapropyl]‐1,4‐phenylene} ( P1 ), poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene} ( P2 ), and poly({9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐(1,4‐phenylene)) ( P3 ). Through the postquaternization treatment of P1 – P3 with methyl iodide, we obtained their cationic water‐soluble conjugated polyelectrolytes (WSCPs): P1′ – P3′ . The water solubility was gradually improved from P3′ to P1′ with increasing contents of hydrophilic side chains. After examining the ultraviolet–visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1′ to P3′ , they exhibited a gradually increased degree of aggregation in H₂O. The PL quantum yields of P1′ – P3′ in H₂O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H₂O. Two structurally analogous water‐soluble trimers of P2′ and P3′ , model compounds 2,7‐bis(9″,9″‐bis{6‴‐[(N,N‐diethyl)‐N‐methylammonium] hexyl}‐2″‐fluorenylethynyl)‐9,9‐bis{6′‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}fluorene hexaiodide and 1,4‐bis(9′,9′‐bis{6″‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}‐2′‐fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)₆⁴⁻ in H₂O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two‐edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778–5794, 2006     

Purines. Part XVI

A series of N‐substituted 8‐aminoxanthines (=8‐amino‐3,7(or 3,9)‐dihydro‐1H‐purine‐2,6‐diones) 8 – 16 and 34 – 37 were synthesized from the corresponding 8‐nitroxanthines 1 – 7, 30 – 33 , and 8‐(phenylazo)xanthines 17 and 18 by catalytic reduction. Another approach was derived from 6‐amino‐5‐(cyanoamino)uracils (=N‐(6‐amino‐1,2,3,4‐tetrahydro‐2,4‐dioxopyrimidin‐5‐yl)cyanamides) 23, 24 , and 27 by base‐catalyzed cyclization yielding 25 – 28 . All 8‐aminoxanthines 8 – 29 and 34 – 37 were acetylated to the corresponding 8‐(acetylamino)xanthines 40 – 57 , and prolonged heating led to 8‐(diacetylamino)xanthines 58 and 59 . Several 8‐aminoxanthines 8 – 13 were diazotized forming 8‐diazoxanthines 60 – 64 . Coupling reactions of isolated 62 and 64 and intermediary formed 8‐diazoxanthines with 1,3‐dimethylbarbituric acid (=1,3‐dimethylpyrimidine‐2,4,6(1H,3H,5H)‐trione; 66 ) resulted in 5‐[(xanthin‐8‐yl)diazenyl]‐1,3‐dimethylbarbituric acids=3,7(or 3,9)‐dihydro‐8‐[2‐(1,2,3,4‐tetrahydro‐1,3‐dimethyl‐2,4‐dioxopyrimidin‐5‐yl)diazenyl]‐1H‐purine‐2,6‐diones) 67 – 80 . The newly synthesized xanthine derivatives were characterized by the determination of their pK_a values, the UV‐ and NMR spectra, as well as elemental analyses.     

Novel Compounds with a Viologen Skeleton and N‐Heterocycles on the Peripheries: Electrochemical and Spectroscopic Properties

The present article deals with novel compounds comprising a redox‐active group as core and a nucleobase in the peripheries, linked covalently via a spacer. The new derivatives 1,1′,1″‐(benzene‐1,3,5‐triyltrimethanediyl)tris{1′‐[3‐(3,4‐dihydro‐5‐methyl‐2,4‐dioxopyrimidin‐1(2H)‐yl)propyl]‐4,4′‐bipyridinium} hexafluorophosphate ( 1 ), 1,1′,1″‐(benzene‐1,3,5‐triyltrimethanediyl)tris{1′‐[2‐(4‐chloro‐7H‐pyrrolo[2,3‐d]pyrimidine‐7‐yl)ethyl]‐4,4′‐bipyridinium} hexachloride ( 2a ) 1

1 The numbering of the pyrrolo[2,3‐d]pyrimidine system follows the IUPAC rules and is different from that of the purine ring system.

, and 1,1′,1″‐(benzene‐1,3,5‐triyltrimethanediyl)tris{1′‐[2‐(2‐amino‐4‐chloro‐7H‐pyrrolo[2,3‐d]pyrimidine‐7‐yl)ethyl]‐4,4′‐bipyridinium} hexabromide ( 2b )¹) were synthesized by nucleobase‐anion alkylation and linked to the 4,4′‐bipyridinium core. UV and CV analyses of these compounds were performed and revealed significantly different properties.     

Facile Synthesis of Novel 3‐(4‐phenylisothiazol‐5‐yl)‐2H‐chromen‐2‐one Derivatives as Potential Anticancer Agents

A series of 3‐(4‐phenylisothiazol‐5‐yl)‐2H‐chromen‐2‐one ( 6a – l ) derivatives has been efficiently synthesized by straightforward sequential reactions. Tandem Vilsmeier Hack reaction/cyclization/bromination/Suzuki cross‐coupling reactions were successfully applied to the preparation of title compounds in good‐to‐high yields. In the synthetic sequences, 3‐chloro‐3‐(2‐oxo‐2H‐chromen‐3‐yl)acrylaldehydes ( 2 ) were found to react with ammonium thiocyanate to yield the corresponding 3‐(isothiazol‐5‐yl)‐2H‐chromen‐2‐ones ( 3 ). These derivatives were brominated with N‐bromo succinamide to yield the corresponding regioselective 3‐(4‐bromoisothiazol‐5‐yl)‐2H‐chromen‐2‐one ( 4 ). Finally, compound 4 was treated with various phenyl/pyrazole/7H –pyrrolo[2,3‐d]pyrimidinyl boronic acids 5a – l in the presence of K₂CO₃ and Pd catalyst in dimethylformamide to yield the corresponding title derivatives 6a – l . All the synthesized compounds were characterized by analytical and spectral studies. All the final compounds were screened against different cancer cell lines (A549, PC3, SKOV3, and B16F10), and among these compounds, 6b , 6g , 6h , and 6l displayed moderate cytotoxic activity against the tested cell lines.     

Derivatives of 2,3‐dihydroimidazo[1,5,4‐ef][1,2,5]‐benzothiadiazepin‐6(4h,7h)‐thione 1,1‐dioxide,a new heterocyclic system related to tibo

The synthesis of derivatives of 2,3‐dihydroimidazo[1,5,4‐ef][1,2,5]benzothiadiazepin‐6(4H,7H)‐thione 1,1‐dioxide is reported starting from N‐substituted ethyl 2‐(5‐chloro‐2‐nitrobenzenesulfonamido)‐2‐alkyl‐acetates. Fundamental steps of the synthetic pathway were: i) intramolecular cyclization of N‐substituted 2‐(2‐amino‐5‐chlorobenzenesulfonamido)‐2‐alkylacetic acids in the presence of N‐(3‐dimethyl‐aminopropyl)‐N′‐ethyl carbodiimide hydrochloride‐N,N‐dimethylaminopyridine complex; ii) building of imidazole ring from 2‐alkyl‐8‐chloro‐2,3‐dihydro‐3‐methyl‐1,2,5‐benzothiadiazepin‐4(5H)‐one 1,1‐dioxide to achieve 2‐alkyl‐9‐chloro‐2,3‐dihydro‐3‐methylimidazo[1,5,4‐ef][1,2,5]benzothiadiazepin‐6(4H,7H)‐one 1,1‐dioxide; iii) preparation of thiocarbonyl derivative by treatment with Lawesson's reagent. Introduction of a 3‐methyl‐2‐butenyl chain at position 2 of above imidazobenzothiadiazepinone required protection at the 7 position with thermally removable tert‐butoxycarbonyl moiety, due to the fact that alkylation of unprotected structure proved to be regioselective for the 7 position.     

Synthesis of 9‐Halogenated 9‐Deazaguanine N7‐(2′‐Deoxyribonucleosides)

The syntheses of N⁷‐glycosylated 9‐deazaguanine 1a as well as of its 9‐bromo and 9‐iodo derivatives 1b , c are described. The regioselective 9‐halogenation with N‐bromosuccinimide (NBS) and N‐iodosuccinimide (NIS) was accomplished at the protected nucleobase 4a (2‐{[(dimethylamino)methylidene]amino}‐3,5‐dihydro‐3‐[(pivaloyloxy)methyl]‐4H‐pyrrolo[3,2‐d]pyrimidin‐4‐one). Nucleobase‐anion glycosylation of 4a – c with 2‐deoxy‐3,5‐di‐O‐(p‐toluoyl)‐α‐D ‐erythro‐pentofuranosyl chloride ( 5 ) furnished the fully protected intermediates 6a – c (Scheme 2). They were deprotected with 0.01M NaOMe yielding the sugar‐deprotected derivatives 8a – c (Scheme 3). At higher concentrations (0.1M NaOMe), also the pivaloyloxymethyl group was removed to give 7a – c , while conc. aq. NH₃ solution furnished the nucleosides 1a – c . In D₂O, the sugar conformation was always biased towards S (67–61%).     

Synthesis of Novel Series of 6‐Chloro‐1,1‐dioxo‐1,4,2‐benzodithiazine Derivatives with Potential Biological Activity

A series of 6′‐chloro‐1′,1′‐dioxo‐2′H‐spiro[benzo[d][1,3,7]oxadiazocine‐4,3′‐(1,4,2‐benzodithiazine)]‐2,6(1H,5H)‐dione derivatives 2a , 2b and 3a , 3b have been synthesized starting from 3‐aminobenzodithiazines 1a , 1b and isatoic anhydride. Subsequent reactions of 2a with 3‐chlorophenyl isocyanate gave condensation products 4 and 5 . Compound 2a was also converted into 3‐(2‐aminobenzamido)‐6‐chloro‐7‐methyl‐1,1‐dioxo‐1,4,2‐benzodithiazine derivatives 6 , 7 , 8 , 9 , 10 . The mechanisms of the reactions are discussed.     

Photochemical Reactions of N‐(2‐Halogenoalkanoyl) Derivatives of Anilines

The photochemical reactions of 2‐substituted N‐(2‐halogenoalkanoyl) derivatives 1 of anilines and 5 of cyclic amines are described. Under irradiation, 2‐bromo‐2‐methylpropananilides 1a – e undergo exclusively dehydrobromination to give N‐aryl‐2‐methylprop‐2‐enamides (=methacrylanilides) 3a – e (Scheme 1 and Table 1). On irradiation of N‐alkyl‐ and N‐phenyl‐substituted 2‐bromo‐2‐methylpropananilides 1f – m , cyclization products, i.e. 1,3‐dihydro‐2H‐indol‐2‐ones (=oxindoles) 2f – m and 3,4‐dihydroquinolin‐2(1H)‐ones (=dihydrocarbostyrils) 4f – m , are obtained, besides 3f – m . On the other hand, irradiation of N‐methyl‐substituted 2‐chloro‐2‐phenylacetanilides 1o – q and 2‐chloroacetanilide 1r gives oxindoles 2o – r as the sole product, but in low yields (Scheme 3 and Table 2). The photocyclization of the corresponding N‐phenyl derivatives 1s – v to oxindoles 2s – v proceeds smoothly. A plausible mechanism for the formation of the photoproducts is proposed (Scheme 4). Irradiation of N‐(2‐halogenoalkanoyl) derivatives of cyclic amines 5a – c yields the cyclization products, i.e. five‐membered lactams 6a , b , and/or dehydrohalogenation products 7a , c and their cyclization products 8a , c , depending on the ring size of the amines (Scheme 5 and Table 3).     

Graphical Abstract: HCA 1/2003

The low solubility of pterins can drastically be improved by N²‐acylation or formation of the N²‐[(dimethylamino)methylene] derivatives. Both types of compounds can be alkylated under Mitsunobu conditions to form from N²‐acylpterins (see 2 and 3 ) and their derivatives (see 5, 6, 8, 9, 11, 13, 15 , and 17 ) selectively the O⁴‐alkyl derivatives 22 – 31 , whereas the electron‐donating [(dimethylamino)methyleneamino function in 46 – 51 gives, in a selective reaction, the N(3)‐substitution (→ 52 – 61 ). N²,N²‐Dimethylpterins and 18 and 19 and N²‐methylpterins 20 and 21 direct alkylation also to the O⁴‐position (→ 32 – 35, 38 and 39 ). Deacylation can be achieved under very mild conditions by solvolysis with MeOH ( 22 → 40, 26 → 41 ), and displacement of the O⁴‐[2‐(4‐nitrophenyl)ethyl] group proceeds with ammonia at room temperature to the corresponding pteridin‐2,4‐diamines 42 – 45 . Cleavage of the N²‐[(dimethylamino)methylene] group works well with ammonia (→ 62 – 67 ). The advantage of applying the 2‐(4‐nitrophenyl)ethyl (npe) group as blocking group is seen in its selective removal by 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) under aprotic conditions without harming the other substituents.     

Synthesis and Reactions of New Thiazoles and Pyrimidines Containing Sulfonate Moiety

Treatment of 2‐tosyloxybenzylidinethiosemicarbazone ( 2 ) with active halo compounds afforded thiazoles 3 – 5 . Moreover, reaction of compound 2 with acetic anhydride or dimethylformamide dimethylacetal gave N,N diacetyl 6 and dimethylamino derivatives 7 , respectively. Cyclization of thiazole derivatives 3 with some arylidenemalononitriles yielded thiazolo[2,3‐d]pyrans 8 – 12 . Multicomponent reaction of 2‐tosyloxybenzaldehyde ( 1 ) with urea, thiourea, or compound 2 and ethyl acetoacetate or acetylacetone afforded pyrimidines 13 – 14 . The structures of compounds were elucidated by elemental and spectral analyses.     

The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 22 Dibenzo[f,h]benzothieno[2,3‐c]quinoline,dibenzo[f,h]benzothieno[2,3‐c][1,2,4]triazolo[4,3‐a]quinoline and dibenzo[f,h]naphtho[2′,1′:4,5]thieno[2,3‐c]quinoline

Photocyclization of 3‐chloro‐N‐(9‐phenanthryl)benzo[b]‐thiophene‐2‐carboxamide ( 3 ) and 3‐chloro‐N‐(9‐phenanthryl)‐naphtho[1,2‐b]thiophene‐2‐carboxamide ( 10 ) yielded dibenzo[f,h]benzothieno[2,3‐c]‐quinolin‐10(9H)‐one ( 4 ) and dibenzo[f,h]naphtho[2′,1′:4,5]thieno[2,3‐c]quinolin‐10(9H)‐one ( 11 ), respectively. Further elaboration of the lactams provided three novel unsubstituted new ring systems.     

Synthesis of (2S)‐2‐(Benzoylamino)‐3‐(heteroaryl)propyl Benzoates

(3E,5S)‐1‐Benzoyl‐5‐[(benzoyloxy)methyl]‐3‐[(dimethylamino)methylidene]pyrrolidin‐2‐one ( 9 ) was prepared in two steps from commercially available (S)‐5‐(hydroxymethyl)pyrrolidin‐2‐one ( 7 ) (Scheme 1). Compound 9 gave, in one step, upon treatment with various C,N‐ and C,O‐1,3‐dinucleophiles 10 – 18 , the corresponding 3‐(quinolizin‐3‐yl)‐ and 3‐(2‐oxo‐2H‐pyran‐3‐yl)‐substituted (2S)‐2‐(benzoylamino)propyl benzoates 19 – 27 (Schemes 1 and 2).     

The Synthesis of Epiboxidine and Related Analogues as Potential Pharmacological Agents

Methyl epiboxidine‐N‐carboxylate ( 8 ) was synthesized from 7 under reductive Heck conditions (Scheme 2). The C? C coupling of the new epiboxidine analog 9 with aryl and heteroaryl halides gave by hydroarylation C‐aryl, N‐(3‐methylisoxazol‐5‐yl)‐substituted tricyclic imides 10a – 10f (Table). The [3+2] cycloaddition of 9 with nitrile oxides yielded the bridged dihydroisoxazole derivatives 11a – 11d with potential biological activity (Scheme 4).     

Synthesis of Some New Benzimidazole–Thiazole Derivatives as Anticancer Agents

4‐(1H‐benzo[d]imidazol‐2‐yl)thiazol‐2‐amine and its 1‐methyl derivative ( 1 ) were reacted with different reagents such as acid anhydrides, malononitrile, chloroacetyl chloride, and aromatic aldehydes to produce the corresponding benzimidazole products 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , respectively. Also, 2‐chloro‐N‐(4‐(1‐methyl‐1H‐benzo[d]imidazol‐2‐yl)thiazol‐2‐yl) acetamide ( 6 ) was reacted with diaminoethane, ortho‐substituted aniline, thioglycolic acid, thiosemicarbazide derivatives, secondary amines, and potassium isothiocyanate to afford the corresponding derivatives 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , respectively. The cytotoxic activity of some newly synthesized derivatives was studied against two different cell lines HepG2 and PC12. Compounds 9 and 15b showed promising anticancer activity against both types of the tested cancerous cell lines.     

Synthesis and Reactivity in [3+2] Cycloadditions of Isoxanthopterin N(5)‐Oxides – A New Synthesis of 6‐Substituted Pteridinediones

Intramolecular condensation of the N‐(4‐amino‐5‐nitrosopyrimidin‐4‐yl)‐2‐chloroacetamide 2 led to the pteridinone N(5)‐oxide 4 , while treatment of 2 with Me₃P yielded the 8‐(chloromethyl)purine 3 . A high‐yielding [3+2] dipolar cycloaddition of the N(5)‐oxide 4 to electron‐poor dipolarophiles, followed by spontaneous N,O‐bond cleavage, gave the C(6)‐substituted pteridinones 8a – 8d that were deprotected to provide the pteridine‐4,7(3H,8H)‐diones 9a – 9d , constituting a new synthesis of pterinones possessing a functionalised side chain at C(6).     

Synthesis,structural characterization and in vitro cytotoxicity of diorganotin complexes with Schiff base ligands derived from 3‐hydroxy‐2‐naphthoylhydrazide

A series of diorganotin complexes with Schiff base ligands, (E)‐N′‐(5‐bromo‐2‐hydroxybenzylidene)‐3‐hydroxy‐2‐naphthohydrazide, H₂L1, and (E)‐N′‐(5‐chloro‐2‐hydroxybenzylidene)‐3‐hydroxy‐2‐naphthohydrazide, H₂L2, were synthesized and characterized by elemental analysis, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The molecular structures of the complexes, [(5‐bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]di(o‐chlorobenzyl)tin(IV) 6 and [(5‐chloro‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibutyltin(IV) 9, were determined through single‐crystal X‐ray diffraction and revealed a distorted trigonal‐bipyramidal configuration. The in vitro cytotoxic activity of the Schiff bases and their diorganotin complexes was also evaluated against several human carcinoma cell lines, namely HT29 (human colon carcinoma cell line), SKOV‐3 (human ovarian cancer cell line), MCF7 (hormone‐dependent breast carcinoma cell line) and MRC5 (non‐cancer human fibroblast cell line). [(5‐Bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibutyltin(IV) 2 and [(5‐bromo‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dibenzyltin(IV) 5 were the most active diorganotin complexes of H₂L1 ligand. Among the diorganotin complexes of H₂L2 ligand, [(5‐chloro‐2‐oxidobenzylidene)‐3‐hydroxy‐2‐naphthohydrazidato]dicyclohexyltin(IV) 11 showed good cytotoxic activity against all the tested cell lines. As such, the above compounds can be considered agents with potential anticancer activities, and can therefore be investigated further in in vitro or in vivo anticancer studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Convenient Synthesis of Some Novel Pyridazinone‐Bearing Triazole Moieties

The chemoselective reactions of 2‐(5‐mercapto‐4‐phenyl‐4H‐[1,2,4]triazol‐3‐ylmethyl)‐6‐p‐tolyl‐4,5‐dihydro‐2H‐pyridazin‐3‐one ( 3 ) with different electrophiles were evaluated. Triazole 3 reacted with alkyl halides in the presence of triethylamine in alcohol to give the corresponding S‐substituted derivatives. On the basis of S‐chemoselective reactions of triazole 3 , a series of amino acid 10a – d and dipeptide derivatives 12a – d were prepared via azide coupling of the corresponding hydrazides 9 and 15 with amino acid ester hydrochlorides, respectively. N‐Substituted triazoles 6a – c or 7a – d attached to pyridazin‐3‐one moiety were successfully formed by the reaction of 3 with activated acrylic acid derivatives or with amines. Antibacterial activities of the synthesized derivatives were investigated through correlation with Escherichia coli FabH inhibitory activities using molecular modeling docking software. The antimicrobial activity of synthesized compounds was evaluated, showing best inhibition zone for N‐substituted carboxylic acid 5a and N‐substituted nitrile 5c parallel to the molecular modeling studies.     

Synthesiss of novel 3‐(2‐thienyl)‐1,2‐diazepino[3,4‐b]quinoxalines with algicidal activity

The reaction of the quinoxaline N‐oxide 1 with thiophene‐2‐carbaldehyde gave 6‐chloro‐2‐[1‐methyl‐2‐(2‐thienylmethylene)hydrazino]quinoxaline 4‐oxide 5 , whose reaction with 2‐chloroacrylonitrile afforded 8‐chloro‐2,3‐dihydro‐4‐hydroxy‐1‐methyl‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]quinoxaline‐5‐carbonitrile 6 . The reaction of compound 6 with various alcohols in the presence of a base effected alcoholysis to provide the 5‐alkoxy‐8‐chloro‐2,3,4,6‐tetrahydro‐1‐methyl‐4‐oxo‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]‐quinoxalines 7a‐d . The reaction of compounds 7a and 7b with diethyl azodicarboxylate effected dehydrogenation to give the 5‐alkoxy‐8‐chloro‐4,6‐dihydro‐1‐methyl‐4‐oxo‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]‐quinoxalines 8a and 8b , respectively. Compounds 8a and 8b were found to show good algicidal activities against Selenastrum capricornutum and Nitzchia closterium.