Highly Efficient [3 + 2] Cycloaddition: Click Synthesis of Novel 1H‐indol‐3‐yl‐benzo[d]imidazole Bis‐triazoles

A series of novel 1‐((1H‐1,2,3‐triazol‐4‐yl)methyl)‐2‐(1‐((1H‐1,2,3‐triazol‐4‐yl)methyl)‐5‐substituted‐1H‐indol‐3‐yl)‐6‐substituted‐1H‐benzo[d]imidazoles 5a – i have been prepared using click chemistry as an ideal strategy where [3 + 2] cycloaddition of azides with terminal alkynes has been developed as the target compounds. In route‐II, 5‐substituted‐1H‐indole‐3‐carbaldehydes 1a – c react with 5‐substituted orthophenylenediamine 8 to give desired products, that is, 6‐substituted‐2‐(5‐substituted‐1H‐indol‐3‐yl)‐1H‐benzo[d]imidazole 6a – i . Here, 6a – i react with 2 equiv of propargylbromide 7 to give novel 6‐substituted 2‐(5‐substituted‐1‐(prop‐2‐yn‐1‐yl)‐1H‐indol‐3‐yl)‐1‐(prop‐2‐yn‐1‐yl)‐1H‐benzo[d]imidazole 4a – i . 4a – i were reacted with 2 equiv of NaN₃ in t‐butanol/water (1:2) and add catalytic amount of CuSO₄.5H₂O. Stir the reaction mixture at room temperature to get the target products 5a – i . Here, obtained products contain four rings, that is, one indole, two triazoles, and one benzimidazole. The main advantages of this method are short reaction times, easy workup, higher yields (88–92%), and no by‐products formation.     

Synthesis of Some Novel Phenyl Substituted Oxothiazolidin- 1’’,3’’,4’’-thiadiazolo-[3’,4’-b]thiazoline of 3β-Substituted Cholestane

Three title compounds 4a—4c have been synthesized by the cyclodehydration of 1’-benzylidine-4’-(3β-substituted-5α-cholestane-6-yl)thiosemicarbazones 2a—2c with thioglycolic acid followed by the treatment with cold conc. H2SO4 in dioxane. The compounds 2a—2c were prepared by condensation of 3β-substituted-5α-cholestan- 6-one-thiosemicarbazones 1a—1c with benzaldehyde. These thiosemicarbazones 1a—1c were obtained by the reaction of corresponding 3β-substituted-5α-cholestan-6-ones with thiosemicarbazide in the presence of few drops of conc. HCl in methanol. The structures of the products have been established on the basis of their elemental, analytical and spectral data.     

Regioselective 1,3‐Dipolar Cycloadditions of (1Z)‐1‐(Arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide Azomethine Imines to Acetylenic Dipolarophiles

The 5,5‐dimethylpyrazolidin‐3‐one ( 4 ), prepared from ethyl 3‐methylbut‐2‐enoate ( 3 ) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a – i to give the corresponding (1Z)‐1‐(arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide azomethine imines 6a – i . The 1,3‐dipolar cycloaddition reactions of azomethine imines 6a – h with dimethyl acetylenedicarboxylate (=dimethyl but‐2‐ynedioate; 7 ) afforded the corresponding dimethyl pyrazolo[1,2‐a]pyrazoledicarboxylates 8a – h , while by cycloaddition of 6 with methyl propiolate (=methyl prop‐2‐ynoate; 9 ), regioisomeric methyl pyrazolo[1,2‐a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a – i with methyl propiolate ( 9 ) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a – e derived from benzaldehydes 5a – e with a single substituent or without a substituent at the ortho‐positions in the aryl residue, led to mixtures of regioisomers 10a – e and 11a – e . Azomethine imines 6f – i derived from 2,6‐disubstituted benzaldehydes 5f – i gave single regioisomers 10f – i .     

Synthesis and Antimicrobial Activities of Novel 2‐[substituted‐1H‐pyrazol‐4‐yl] Benzothiazoles,Benzoxazoles, and Benzimidazoles

In an endeavor to find a new class of antimicrobial agents, a series of novel substituted benzimidazole, benzoxazole, and benzothiazole derivatives 6 containing pyrazole moiety have been synthesized by reaction of 3‐aryl‐4‐formyl pyrazole 4 with substituted phenylenediamine or o‐aminophenol or o‐aminothiophenol 5 . Reaction of phenyl hydrazine or 2‐hydrazinopyridine 1 with substituted acetophenones 2 gave the corresponding hydrazones 3 , which on Vilsmeier–Haack reaction with POCl₃–DMF gave substituted 3‐aryl‐4‐formyl pyrazoles 4 . All final compounds 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j , 6k were evaluated for in vitro antibacterial activities against Escherichia coli and Staphylococcus aureus strains and in vitro antifungal activity against Candida albicans and Aspergillus niger strains by using serial dilution method. The antimicrobial activities were expressed as the minimum inhibitory concentration in µg/mL. The compound containing benzimidazole and benzoxazole moiety gave better antibacterial and antifungal activities than benzothiazole compounds.     

Exceptional Products of the Desulfurization of N,2-Diaryl-5-(arylimino)- 2,5-dihydro-4-nitroisothiazol-3-amines

The desulfurization of several N,2-diaryl-5-(arylimino)-2,5-dihydro-4-nitroisothiazol-3-amines 5 with Ph₃P led to complex mixtures of products in low yields. For instance, quinoxaline-2-carboxamide 1-oxides of type 6 (Scheme 2) and, in some cases, also 3-nitroquinolines of type 7 (Scheme 5) were isolated. By the desulfurization of the substituted derivatives 5b – e , a rearrangement of the intermediates yielded 6 and 7 with a different substitution pattern from that expected from the starting materials (Scheme 3). The additional formation of two isomeric 1,2,5-oxadiazole-3-carboxamides 8 was observed only in the case of 5d (R¹=R²=F) (Scheme 6). Under the same reaction conditions, the major product of the desulfurization of 5c was the quinoxaline-2-carboxamide 1-oxide 9 (Scheme 7). Reaction mechanisms involving intermediate ketene imines and O transfer from the NO₂ group to the neighboring ketene imine are proposed. The structures of 6a , 6e , 6k , 7b , and 8d were established by X-ray crystallography, while the structure of 9 was elucidated by 2D-NMR spectroscopy and corroborated by X-ray crystallography.     

The Haloboration of Tri‐tert‐butylazadiboriridine NB2R3: Ring Opening versus NB3 Cluster Formation

The azadiboriridine [–BR–NR–BR–] ( 1 ; R = tBu) is bromoborated at the B–B bond by alkyldibromoboranes R′BBr₂ to give the products Br–BR–NR=BR–BR′–Br ( 8 a – g : R′ = Me, Bu, iBu, Bzl, CH₂CHEt₂, CH₂Cy, CH₂(4‐C₆H₄tBu)). Two isomers of each of the products 8 a – g are formed and attributed to a cis/trans isomerism at the BN double bond; the isomerization is followed thermodynamically and kinetically by NMR methods with 8 a – d . The analogous chloroboration of 1 with BCl₃ yields Cl–BR–NR=BR–BCl₂ ( 8 h ), which at ambient temperature undergoes a degenerate exchange of the ligands Cl and BCl₂ along the B–N–B skeleton. At room temperature, the isomer Cl–BR–NR=BCl–BR–Cl ( 8 h ′) is slowly formed by an irreversible exchange of R and Cl along the B–B bond of 8 h . Different from BCl₃, the chloroborane BH₂Cl is simply added to the B–B bond of 1 under formation of the aza‐nido‐tetraborane NB₃R₃H₂Cl ( 2 b ). The chloroborane BHCl₂ gives a mixture of 8 h ′ and 2 b upon addition to 1 , apparently according to a preceding dismutation into BCl₃ and BH₂Cl. The configuration at the B3 atom of the nido‐clusters NB₃R₃H₂X (X = H, Cl) is discussed on the basis of the corresponding model molecules NB₃Me₃H₂X, whose structure and NMR signals are computed by the B3LYP method. The boranes 8 b – g can be debrominated with Li in the presence of tmen on applying ultrasound. The products are found to be the B‐borylated azadiboriridines [–BR–NR–B(BRR′)–] ( 9 b – g ). The 2‐borylazadiboriridines NB₃H₄ ( 9 h ) and NB₃Me₄ ( 9 i ) were found as local minima on the energy hyperface by the B3LYP method, but minima for structural isomers with lower energy were also found; the tetrahedral clusters NB₃R₄ give high‐energy minima with triplet ground states. Computations of the ¹¹B NMR shifts of 9 h and 9 i support the proposed structures of 9 b – g .     

Synthesis and Microbial Studies of New Pyridine Derivatives-Ill

2-Amino substituted benzothiazole 4a--4I and p-acetamidobenzenesulfonyl chloride 2 were used to prepare 2-（p-aminophenylsulfonamido） substituted benzothiazole 6a--6I using mixture of pyridine and acetic anhydride which formed an electrophilic complex （N-acetyl pyridinium） to facilitate condensation to give desired product by removal of HC1. 2-{p-[（3-Carboxypyrid-2-y1）amino]phenylsulfonamido}benzothiazoles 8a--81 were synthesized from 2-chloropyridine-3-carboxylic acid 7 and 6a--6I in 2-ethoxy ethanol using Cu-powder and K2CO3. Acid chlorides 9a--91 were condensed with 2-hydroxyethyl piperazine 10 and 2,3-dichloropiperazine 11 for amide deriva- tives 2-（p-（（3-（4-（2-hydroxyethy1）piperazin-1-ylcarbonyl）pyrid-2-y1）amino）phenylsulfonamido）benzothiazoes 12a -121 and 2-{p-[3-（2,3-dichloropiperazin-l-ylcarbonyl）pyrid-2-ylamino]phenylsulfonamido}benzothiazoles 13a- 131 respectively. The structures of the new compounds have been established on the basis of their chemical analysis and spectral data （IR, 1↑H NMR and mass）. All the compounds have been screened for their antibacterial and antifungal activities.     

Photochemistry of N‐(2‐Acylphenyl)‐2‐methylprop‐2‐enamides: Competition between Photocyclization and Long‐Range Hydrogen Abstraction

The photochemical reactions of various ‘N‐methacryloyl acylanilides’ (=N‐(acylphenyl)‐2‐methylprop‐2‐enamides) have been investigated. Under irradiation, the acyl‐substituted anilides 1a – 1c and 1o afforded exclusively the corresponding quinoline‐based cyclization products of type 2 (Table 1). In contrast, irradiation of the benzoyl (Bz)‐substituted anilides 1e – 1h afforded a mixture of the open‐chain amides 4e – 4h and the cyclization products 2e – 2h . Irradiation of the para‐acyl‐substituted anilides 6a – 6e and 6h afforded the corresponding quinoline‐based cyclization products of type 5 as the sole products (Table 2). The formation of the cyclization products 2a – 2c and 2o can be rationalized in terms of 6π‐electron cyclization, followed by thermal [1,5] acyl migration, and that of compounds 3p, 5a – 5e , and 5h can be explained by a 6π‐electron cyclization only. The formation of the open‐chain amides 4e – 4h probably follows a mechanism involving a 1,7‐diradical, C and a spirolactam of type D (Scheme). Long‐range ζ‐H abstraction by the excited carbonyl O‐atom of the benzoyl group on the aniline ring is expected to proceed via a nine‐membered cyclic transition state, as proposed on the basis of X‐ray crystallographic analyses (Fig. 2).     

Synthesis of Indolones via Radical Cyclization of N‐(2‐Halogenoalkanoyl)‐Substituted Anilines

The radical reactions of N‐(2‐halogenoalkanoyl)‐substituted anilines (anilides) of type 1 have been investigated under various conditions. Treatment of compounds 1a – 1o with Bu₃SnH in the presence of (2,2′‐azobis(isobutyronitrile) (AIBN) afforded a mixture of the indolones (oxindoles) 2a – 2o and the reduction products 5a – 5o (Table 1). In contrast, the N‐unsubstituted anilides 1p – 1s, 1u , and 1v gave the corresponding reduction products exclusively (Table 1). Similar results were obtained by treatment of 1 with Ni powder (Table 2) or wth Et₃B (Table 3). Anilides with longer N‐(phenylalkyl) chains such as 6 and 7 were inert towards radical cyclization, with the exception of N‐benzyl‐2‐bromo‐N,2‐dimethylpropanamide ( 6b ), which, upon treatment with Ni powder in i‐PrOH, afforded the cyclized product 9b in low yield (Table 4). Upon irradiation, the extended anilides 6, 7, 10 , and 11 yielded the corresponding dehydrobromination products exclusively (Table 5).     

Radical Cyclization Reactions via Manganese(III) Acetate Leading to 2‐Thienyl‐Substituted Dihydrofuran Compounds

The 2‐thienyl‐substituted 4,5‐dihydrofuran derivatives 3 – 8 were obtained by the radical cyclization reaction of 1,3‐dicarbonyl compounds 1a – 1f with 2‐thienyl‐substituted conjugated alkenes 2a – 2e by using [Mn(OAc)₃] (Tables 1–5). In this study, reactions of 1,3‐dicarbonyl compounds 1a – 1e with alkenes 2a – 2c gave 4,5‐dihydrofuran derivatives 3 – 5 in high yields (Tables 1–3). Also the cyclic alkenes 2d and 2e gave the dihydrobenzofuran compounds, i.e., 6 and 7 in good yields (Table 4). Interestingly, the reaction of benzoylacetone (=1‐phenylbutane‐1,3‐dione; 1f ) with some alkenes gave two products due to generation of two stable carbocation intermediates (Table 5).     

Synthesis,Characterization and Crystal Structure of Some Novel 1‐(3,5‐Dimethyl‐1H‐pyrazol‐1‐yl)‐3‐(substituted anilino)propan‐1‐ones

Michael addition of some substituted anilines to methyl acrylate in acidic medium afforded the methyl 3-(substituted anilino)propionates (1a—1i), which on treatment with hydrazine hydrate in methanol were converted into corresponding 3-(substituted anilino) propionohydrazides (2a—2i) in good yields. Microwave irradiation of the latter with pentane-2,4-dione afforded 1-(3,5-dimethyl-1H-pyrazol-1-yl)-3-(substituted anilino)propan-1-ones (3a—3i) under solventless conditions. The structures were confirmed by spectroscopic data, elemental analyses and in case of the 3h by single crystal X-ray diffraction data.     

Diastereo‐ and Enantioselective Intramolecular [2+2] Photocycloaddition Reactions of 3‐(ω′‐Alkenyl)‐ and 3‐(ω′‐Alkenyloxy)‐Substituted 5,6‐Dihydro‐1H‐pyridin‐2‐ones

3‐(ω′‐Alkenyl)‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones 2 – 4 were prepared as photocycloaddition precursors either by cross‐coupling from 3‐iodo‐5,6‐dihydro‐1H‐pyridin‐2‐one ( 8 ) or—more favorably—from the corresponding α‐(ω′‐alkenyl)‐substituted δ‐valerolactams 9 – 11 by a selenylation/elimination sequence (56–62 % overall yield). 3‐(ω′‐Alkenyloxy)‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones 5 and 6 were accessible in 43 and 37 % overall yield from 3‐diazopiperidin‐2‐one ( 15 ) by an α,α‐chloroselenylation reaction at the 3‐position followed by nucleophilic displacement of a chloride ion with an ω‐alkenolate and oxidative elimination of selenoxide. Upon irradiation at λ=254 nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5 , tethered by a two‐atom chain, exclusively delivered the respective crossed products 19 and 20 , and substrates 3 , 5 , and 6 , tethered by longer chains, gave the straight products 21 – 23 . The completely regio‐ and diastereoselective photocycloaddition reactions proceeded in 63–83 % yield. Irradiation in the presence of the chiral templates (?)‐ 1 and (+)‐ 31 at ?75 °C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85 % ee. Truncated template rac‐ 31 was prepared as a noranalogue of the well‐established template 1 in eight steps and 56 % yield from the Kemp triacid ( 24 ). Subsequent resolution delivered the enantiomerically pure templates (?)‐ 31 and (+)‐ 31 . The outcome of the reactions is compared to the results achieved with 4‐substituted 5,6‐dihydro‐1H‐pyridin‐2‐ones and quinolones.     

Synthesis of 3‐Alkoxybenzo[c]thiophen‐1(3H)‐ones by Hydrolysis of N‐Substituted 3‐Alkoxybenzo[c]thiophen‐1(3H)‐imines Derived from 1‐Bromo‐2‐(dialkoxymethyl)benzenes and Isothiocyanates

A convenient procedure for the preparation of a new type of thiophthalides, 3‐alkoxybenzo[c]thiophen‐1(3H)‐ones 4 and 9 has been developed. Thus, 1‐(dialkoxymethyl)‐2‐lithiobenzenes, generated by Br/Li exchange between 2‐bromo‐1‐(dialkoxymethyl)benzenes 1 and 6 , and BuLi, react with isothiocyanates to afford N‐substituted 2‐(dialkoxymethyl)benzothioamides 2 and 7 , which, on treatment with a catalytic amount of TsOH?H₂O, give N‐substituted 3‐alkoxybenzo[c]thiophen‐1(3H)‐imines 3 and 8 . The latter are hydrolyzed under acidic conditions to the desired products 4 and 9 , respectively.     

Mono- and Dialkylation of Derivatives of (1R, 2S)-2-Hydroxycyclopentanecarboxylic Acid and -cyclohexanecarboxylic acid via bicyclic dioxanones: Selective generation of three contiguous stereogenic centers on a cyclohexane ring

Ethyl (1R, 2S)-2-hydroxycyclopentanecarboxylate and -cyclohexanecarboxylate ( 1a and 2a , respectively) obtained in 40 and 70% yield by reduction of 3-oxocyclopentanecarboxylate and cyclohexanecarboxylate, respectively (Scheme 2), with non-fermenting yeast, are converted to bicyclic dioxanone derivatives 3 and 4 with formaldehyde, isobutyraldehyde, and pivalaldehyde (Scheme 3). The Li-enolates of these dioxanones are alkylated (→ 5a – 5i , 5j , 6a – 6g ), hydroxyalkylated (→ 51, m, 6d, e ), acylated (→ 5k, 6c ) and phenylselenenylated (→ 7 – 9 ) with usually high yields and excellent diastereoselectivities (Scheme 3, Tables and 2). All the major isomers formed under kinetic control are shown to have cis-fused bicyclic structures. Oxidation of the seleno compounds 7–9 leads to α, β-unsaturated carbonyl derivatives 10 – 13 (Scheme 3) of which the products 12a – c with the C?C bond in the carbocyclic ring (exocyclic on the dioxanone ring) are most readily isolated (70–80% from the saturated precursors). Michael addition of Cu(I)-containing reagents to 12a – c and subsequent alkylations afford dioxanones 14a – i and 16a – d with trans-fused cyclohoxane ring (Scheme 4). All enolate alkylations are carried out in the presence of the cyclic urea DMPU as a cosolvent. The configuration of the products is established by NMR measurements and chemical correlation. Some of the products are converted to single isomers of monocyclic hydroxycyclopentane ( 17 – 19 ) and cyclohexane derivatives ( 20 – 23 ; Scheme 5). Possible uses of the described reactions for EPC synthesis are outlined. The observed steric course of the reactions is discussed and compared with that of analogous transformations of monocyclic and acyclic derivatives.     

Notiz zur Synthese von Alkyl-, Cycloalkyl- und Aryl-3-aminophenylsulfonen

Syntheses of Some Alkyl, Cycloalkyl and Aryl 3-Aminophenyl Sulfones Syntheses of alkyl ( 1a – 1i, 1m ), cycloalkyl ( 1j, 1k ) and aryl ( 1l ) 3-aminophenyl sulfones were achieved by ethanolic Béchamp-reduction of the appropriate 3-nitrophenyl sulfones ( 3a – 3m ). The alkyl ( 3a – 3i ) and cycloalkyl ( 3j, 3k ) 3-nitrophenyl sulfones were prepared via nitration of their respective sulfones ( 2a – 2k ). Methyl (3-nitrophenyl) sulfone ( 3a ) was also prepared by condensation of 3-nitrobenzenesulfinic acid ( 4 ) with bromoacetic acid to 3-nitrophenylsulfonyl-acetic acid ( 5 ) followed by decarboxylation.     

Photoisomerization of 2H,6H-thiin-3-one 1-oxides to 3H,7H-[1,2]oxathiepin-4-ones

Oxidation of 2H, 6H-thiin-3-ones 1a – c with 3-chloroperbenzoic acid affords the corresponding 1-oxides 2a – c . On irradiation (350 nm) in either benzene or MeCN, these cyclic sulfoxides 2 isomerize to 3H, 7H-1,2-oxathiepin-4-ones 3 . The tetramethyl derivative 3a is isolated by flash chromatography at ?10°, but, at higher temperatures, it undergoes ring contraction and H₂O elimination to give 4,4-dimethyl-2(2-methylprop-2enylidene)thietan-3-one ( 4 ). Diemthyloxathiepinones 3b and 3c undergo ring contraction in MeOH to afford 1-(4-methylthiophen-2-yl)ethanone ( 5 ) and two diastereoisomeric 4,4-dimethyl-2-methoxy-2-(1-methoxyethyl)thietan-3-ones ( 6 and 7 , respectively).     

Regioselectivity of the 1,3‐Oxathiolane Formation in the Lewis Acid‐Catalyzed Reaction of Thioketones with Asymmetrically Substituted Oxiranes

The reactions of the aromatic thioketone 4,4′‐dimethoxythiobenzophenone ( 1 ) with three monosubstituted oxiranes 3a – c in the presence of BF₃⋅Et₂O or SnCl₄ in dry CH₂Cl₂ led to the corresponding 1 : 1 adducts, i.e., 1,3‐oxathiolanes 4a – b with R at C(5) and 8c with Ph at C(4). In addition, 1,3‐dioxolanes 7a and 7c , and the unexpected 1 : 2 adducts 6a – b were obtained (Scheme 2 and Table 1). In the case of the aliphatic, nonenolizable thioketone 1,1,3,3‐tetramethylindane‐2‐thione ( 2 ) and 3a – c with BF₃⋅Et₂O as catalyst, only 1 : 1 adducts, i.e. 1,3‐oxathiolanes 10a – b with R at C(5) and 11a – c with R or Ph at C(4), were formed (Scheme 6 and Table 2). In control experiments, the 1 : 1 adducts 4a and 4b were treated with 2‐methyloxirane ( 3a ) in the presence of BF₃⋅Et₂O to yield the 1 : 2 adduct 6a and 1 : 1 : 1 adduct 9 , respectively (Scheme 5). The structures of 6a , 8c , 10a , 11a , and 11c were confirmed by X‐ray crystallography (Figs. 1 – 5). The results described in the present paper show that alkyl and aryl substituents have significant influence upon the regioselectivity in the process of the ring opening of the complexed oxirane by the nucleophilic attack of the thiocarbonyl S‐atom: the preferred nucleophilic attack occurs at C(3) of alkyl‐substituted oxiranes (O−C(3) cleavage) but at C(2) of phenyloxirane (O−C(2) cleavage).     

Synthesis of 9-(trifluoromethyl)pyrido[1′,2′:1,2]-imidazo[4,5-b]quinoxalines

9-(Trifluoromethyl)pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines (9-CF₃-PIQs) were obtained from the cyclization of 2-amino-3-chloro-6-(trifluoromethyl)quinoxaline ( 1a ) with some substituted pyridines. 3-[2-(4-Pyridyl)ethenyl]-9-CF₃-PIQ, one of thus obtained 9-CF₃-PIQs, cyclized with another molecule of 1a to produce the dihydro bis-PIQ-ethene derivative.     

Über die Bildung cyclischer Ionen und bicylischer Übergangszustände beim Zerfall substituierter α,ω-Alkandiamine im Massenspektrometer. 23. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

Formation of cyclic ions and bicyclic transition states in the mass spectral decomposition of substituted α,ω-alkanediamines. N-Phenethyl-N(4-acetamidobutyl)-p-toluene-sulfonamide ( 4 ) and its homologues were synthesized and the mass spectral behaviour investigated. After loss of a benzyl radical from the molecular ion two different fragmentation reactions are observed. The lower homologous members – namely compounds 1 , 2 and 3 – lose ketene by formation of cyclic ions (Scheme 1). The higher homologues of this series of compounds ( 4 , 5 , 6 ) show a pronounced (to 18% ∑₅₀) loss of p-toluene sulfonic acid. This decomposition reaction proceeds presumably through a bicyclic transition state (Scheme 3).     

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).