Diels–Alder Additions,Ene Reactions,and Condensations of 4‐(Acylamino)‐5‐nitrosopyrimidines – Synthesis of 8‐Substituted Guanines and of 6‐Substituted Pteridinones

4‐(Acylamino)‐5‐nitrosopyrimidines react either by a reductive condensation to provide 8‐substituted guanines, or by a Diels–Alder cycloaddition, or an ene reaction, to provide 6‐substituted pteridinones, depending on the nature of the acyl group and the reaction conditions. Experimental details are provided for the transformation of (acylamino)‐nitrosopyrimidines to 8‐substituted guanines, and the scope of the reaction is further demonstrated by transforming the trifluoro acetamide 25 to the 8‐(trifluoromethyl)guanine ( 27 ), and the N,N′‐bis(nitrosopyrimidinyl)‐dicarboxamide 29 to the (R,R)‐1,2‐di(guan‐8‐yl)ethane‐1,2‐diol ( 32 ). An intramolecular Diels–Alder reaction of the N‐sorbyl (=N‐hexa‐2,4‐dienoyl) nitrosopyrimidine 10 , followed by a spontaneous elimination to cleave the N,O bond of the initial cycloaddition product provided the pteridinones 14 or 15 , characterized by a (Z)‐ or (E)‐3‐hydroxyprop‐1‐enyl group at C(6). Treatment of 10 with Ph₃P led to the C(8)‐penta‐1,3‐dienyl‐guanine 18 . The ene reaction of the N‐crotonyl (=N‐but‐2‐enoyl) nitrosopyrimidine 19 provided the 6‐vinyl‐pteridinone 20a that dimerized readily to 21a , while treatment of 19 with Ph₃P led in high yield to 8‐(prop‐1‐enyl)guanine ( 23 ). The structure of the dimer 21 was established by X‐ray analysis of its bis(N,N‐dimethylformamidine) derivative 21b . The crystal structure of the nitroso amide 10 is characterized by two molecules in the centrosymmetric unit cell. Intermolecular H‐bonds connect the amino group to the amide carbonyl and to N(1). The crystalline bis(purine) 30 forms a left‐handed helix with four molecules per turn and a pitch of 30.2 Å.     

A New Synthesis of Pteridines Substituted with Branched and Linear Alkenyl Groups at C(6). The Nitroso‐Ene Reaction of 4‐(Alkenoylamino)‐5‐nitrosopyrimidines

Pteridines substituted with a 1,1‐, 1,2‐, or 1,1,3‐substituted alkenyl group (mostly (E)‐configured) at C(6) were synthesized in high yields by the intramolecular nitroso‐ene reaction of 4‐(alkenoylamino)‐2‐amino‐6‐benzyloxy‐5‐nitroso‐ and 4‐(alkenoylamino)‐2,6‐diamino‐5‐nitrosopyrimidines. Thus, the N‐alkenoyl nitrosopyrimidines 4 and 5 provided the pteridines 6 and 7 , respectively, characterized by a 1,2‐disubstituted (E)‐alkenyl substituent, the C(4)‐(E)‐geranoyl amide 13 led regio‐ and stereoselectively to the (E)‐1,1,2‐trisubstituted alkenyl‐pteridine 16 , and the C(4)‐(Z) isomer 14 led to 17 possessing a 1,1‐disubstituted alkenyl group. The trifluoromethylated butenoyl amide 15 possessing a less highly nucleophilic alkenoyl group reacted more slowly to give the trifluoromethylated vinylpteridine 18 . Also the 4‐(alkenoylamino)‐2,6‐diamino‐5‐nitrosopyrimidine 20 reacted more slowly than 4 and 5 , and provided the pteridines 23 ; introduction of additional N‐acyl groups as in 21 and 22 led to a considerably faster ene reaction. The X‐ray crystal structure analysis of the nitroso amide 15 shows eight symmetrically independent molecules in the unit cell. In the crystalline state, the N,N‐dimethylformamidine derivative 9 of 6 forms a centrosymmetric dimer with the 7,8‐lactam group connected by intermolecular hydrogen bonds.     

Stereoselective SE2′ Protonation of α‐Hydroxyallylsilanes Mediated by a Brook Rearrangement

Brooked up! Treatment of (R,Z)‐3‐(tert‐butyldimethylsilyl)‐1‐cyano‐3‐hydroxyprop‐1‐enyl carbamate with a catalytic amount of a base afforded (S,E)‐3‐(tert‐butyldimethylsilyloxy)‐1‐cyanoallyl diisopropylcarbamate, showing that S_E2′‐type reaction of allylsilicates proceeds in an anti fashion. The overall process is equivalent to trapping of an enantioenriched C‐chiral carbanion at the α‐position of nitrile group in up to 77 % ee (see scheme).

     

Intramolecular [2+2] Photocycloaddition of 3‐ and 4‐(But‐3‐enyl)oxyquinolones: Influence of the Alkene Substitution Pattern,Photophysical Studies,and Enantioselective Catalysis by a Chiral Sensitizer

The intramolecular [2+2] photocycloaddition of four 4‐(but‐3‐enyl)oxyquinolones (substitution pattern at the terminal alkene carbon atom: CH₂, Z‐CHEt, E‐CHEt, CMe₂) and two 3‐(but‐3‐enyl)oxyquinolones (substitution pattern: CH₂, CMe₂) was studied. Upon direct irradiation at λ=300 nm, the respective cyclobutane products were formed in high yields (83–95 %) and for symmetrically substituted substrates with complete diastereoselectivity. Substrates with a Z‐ or E‐substituted terminal double bond showed a stereoconvergent reaction course leading to mixtures of regio‐ and diastereomers with almost identical composition. The mechanistic course of the photocycloaddition was elucidated by transient absorption spectroscopy. A triplet intermediate was detected for the title compounds, which–in contrast to simple alkoxyquinolones such as 3‐butyloxyquinolone and 4‐methoxyquinolone–decayed rapidly (τ≈1 ns) through cyclization to a triplet 1,4‐diradical. The diradical can evolve through two reaction channels, one leading to the photoproduct and the other leading back to the starting material. When the photocycloaddition was performed in the presence of a chiral sensitizer (10 mol %) upon irradiation at λ=366 nm in trifluorotoluene as the solvent, moderate to high enantioselectivities were achieved. The two 3‐(but‐3‐enyl)oxyquinolones gave enantiomeric excesses (ees) of 60 and 64 % at ?25 °C, presumably because a significant racemic background reaction occurred. The 4‐substituted quinolones showed higher enantioselectivities (92–96 % ee at ?25 °C) and, for the terminally Z‐ and E‐substituted substrates, an improved regio‐ and diastereoselectivity.     

Synthesis of 4‐Aryl‐1,7‐naphthyridine‐2(1H)‐thiones by the Electrocyclic Reaction of 4‐(1‐Arylalk‐1‐enyl)‐3‐isothiocyanatopyridines Generated in situ from the Corresponding Isocyanides

A convenient synthis for 4‐substituted and 3,4‐disubstituted 1,7‐naphthyridine‐2(1H)‐thiones 7 has been developed. The method is based on the electrocyclic reaction of 4‐(1‐arylalk‐1‐enyl)‐3‐isothiocyanatopyridines 6 , generated in situ by the treatment of the respective isocyanides 5 with S₈ in the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from commercially available pyridin‐3‐amine by conventional organic reactions.     

Three New Neolignans from the Aril of Myristica fragrans

Three new neolignans, named 1‐deoxycarinatone ( 1 ), isodihydrocarinatidin ( 2 ), and isolicarin A ( 3 ), together with the known neolignan (+)‐dehydrodiisoeugenol ( 4 ), were isolated from mace (the aril of Myristica fragrans Houtt .). Their structures were elucidated as 2‐[(1S)‐2‐(4‐hydroxy‐3‐methoxyphenyl)‐1‐methylethyl]‐6‐methoxy‐4‐(prop‐2‐enyl)phenol ( 1 ), 4‐[(2R,3R)‐2,3‐dihydro‐7‐methoxy‐3‐methyl‐5‐(prop‐2‐enyl)benzofuran‐2‐yl]‐2‐methoxyphenol ( 2 ), and 4‐{(2S,3R)‐2,3‐dihydro‐7‐methoxy‐3‐methyl‐5‐[(1E)‐prop‐1‐enyl]benzofuran‐2‐yl}‐2‐methoxyphenol ( 3 ) on the basis of spectroscopic data.     

A New Synthesis of Ciliapterin and Dictyopterin. Ene Reactions of (Alkenylamino)‐nitroso‐pyrimidines

A comparison of the reactivity of (acylamino)‐nitroso‐pyrimidines 1 and the alkenylamino analogue 17 in intramolecular ene reactions showed the considerably lower reactivity of 17 , leading to the pteridine 18 . Pteridin‐7‐one 11 resulting from 1 (R¹=OBn, R²=Me) was transformed into 4‐(benzyloxy)‐6‐[(E)‐prop‐1‐enyl]pteridin‐2‐amine ( 13 ) by O‐triflation, followed by reduction with LiBHEt₃, while the 4‐MeO analogue 18 was prepared by spontaneous oxidation of the initial ene product of 17 . The (alkenylamino)‐nitroso‐pyrimidine 17 was synthesized by substitution of the dimethoxy‐nitroso‐pyrimidine 16 with the allylamine 15 . Ciliapterin ( 5 ) and dictyopterin ( 7 ) were synthesized from pteridine 18 by a Sharpless asymmetric dihydroxylation.     

Fe‐Catalyzed Multicomponent Reactions: The Regioselective Alkoxy Allylation of Activated Olefins and its Application in Sequential Fe Catalysis

We present herein a versatile and broadly applicable Fe‐catalyzed regioselective alkoxy allylation of activated double bonds. Substituted allylic carbonates are converted into the corresponding σ‐enyl Fe complexes by reaction with Bu₄N[Fe(CO)₃(NO)] (TBAFe) at 30 °C. The liberated alkoxide adds to an activated double bond with the generation of a C‐nucleophile, which is trapped by the σ‐enyl Fe complex in a regioselective manner. Alternatively, the alkoxide acts as a base in deprotonating an external pronucleophile, which undergoes Michael addition. The method is characterized by a broad functional group tolerance, mild reaction conditions, low catalyst loadings, and high regioselectivities in favor of the ipso‐substitution product.     

Modification Pathways for Copoly(2‐oxazoline)s Enabling Their Application as Antireflective Coatings in Photolithography

Chromophore‐functionalized copoly(2‐oxazoline)s are successfully evaluated as bottom antireflective coatings (BARCs) in high‐resolution photolithography. With respect to UV light sources used in photolithographic production routines, anthracene is chosen as a chromophore. For application as polymer in BARCs, the copolymer poly(2‐ethyl‐2‐oxazolin)₄₅‐stat‐poly(2‐dec‐9′‐enyl‐2‐oxazolin)₂₀‐stat‐poly(2‐(3′‐(1″‐(anthracen‐9‐ylmethyl)‐1″,2″,3″‐triazol‐4‐yl)propyl)‐2‐oxazolin)₃₅ can be synthesized by the Huisgen cycloaddition click reaction of the copolymer poly(2‐ethyl‐2‐oxazolin)₄₅‐stat‐poly(2‐dec‐9′‐enyl‐2‐oxazolin)₂₀‐stat‐poly(2‐pent‐4′‐inyl‐2‐oxazolin)₃₅ and the corresponding azide‐functionalized anthracenes. These copolymers can be crosslinked by the thermally induced thiol‐ene reaction involving the unsaturated C=C bonds of the poly(2‐dec‐9′‐enyl‐2‐oxazoline) repetition units and a multifunctional thiol as crosslinker. Tests of this BARC in a clean room under production conditions reveal a significant decrease of the swing‐curve of a chemically amplified positive photoresist by more than 50%, hence significantly increasing the resolution of the photoresist.

     

Isolation of a New Carotenoid and Two New Carotenoid Glycosides from Curtobacterium flaccumfaciens pvar poinsettiae

An efficient method for the extraction of the carotenoids from Curtobacterium flaccumfaciens pvar poinsettiae was developed. The glucosides of C.p. 450 (=(all‐E,2R,2′R)‐2‐[4‐(β‐D ‐glucopyranosyloxy)‐3‐methylbut‐2‐enyl]‐2′‐(4‐hydroxy‐3‐methylbut‐2‐enyl)‐β, β‐carotene; 4 ) and of C.p. 473 (=(all‐E,2R,2′S)‐2‐[4‐(β‐D ‐glucopyranosyloxy)‐3‐methylbut‐2‐enyl]‐2′‐(3‐methylbut‐2‐enyl)‐3′,4′‐didehydro‐1′,2′‐dihydro‐β,ψ‐caroten‐1′‐ol; 5 ) were isolated for the first time. In addition, the hitherto unknown 3′,4′‐dihydro derivative of C.p. 450, called C.p. 460 (=(all‐E,2R,2′R)‐2‐(4‐hydroxy‐3‐methylbut‐2‐enyl)‐2′‐(3‐methylbut‐2‐enyl)‐1′,2′‐dihydro‐β,ψ‐caroten‐1′‐ol; 6 ), was identified. The structures were established by UV/VIS, CD, ¹H‐ and ¹³C‐NMR, and mass spectra.     

Enamides via Long‐Distance Migration of Double Bonds

A new method for preparation of enamides (N‐(alken‐1‐yl) amides) by means of the ‘long‐distance' migration of the double bond in unsaturated amides in the presence of [Fe(CO)₅] is described. The method is shown to be particularly useful for the isomerization of N‐(but‐3‐enyl)amides, while, in the case of N‐(pent‐4‐enyl) and N‐(hex‐5‐enyl) amides the mixture of products was formed and the yield of the enamide was relatively low.     

Synthesis and Structures of β‐Diketoiminate Complexes of Magnesium

The reaction of the β‐diketoiminate lithium complex (dipp)NacNacLi · OEt₂ ((dipp)NacNac = 2‐((2,6‐diisopropylphenyl)amino)‐4‐((2,6‐diisopropylphenyl)imino)‐pent‐2‐enyl) with iPrMgCl and MgI₂ yield the corresponding (dipp)NacNacMgiPr · OEt₂ ( 1 ) and (dipp)NacNacMgI · OEt₂ ( 2 ). The reaction of 2 with NaBH₄ in diethylether gives (dipp)NacNacMg(μ‐H)₃BH · OEt₂ ( 3 ). The core element of compounds 1 – 3 is a six‐membered ring formed by N(1)–C(1)–C(2)–C(3)–N(2) and magnesium. The structures of 1 and 2 show the β‐diketoiminate backbone in a boat‐conformation with the tetrahedrally coordinated metal center at the prow and the opposing carbon atom at the stern. The magnesium atom in 3 is octahedrally coordinated and out of the β‐diketoiminate plane.     

Studies on the Reaction of α‐Chloroformylarylhydrazine Hydrochloride with Imidazole and 1,2,4‐Triazole

α‐Imidazolformylarylhydrazine 2 and α‐[1,2,4]triazolformylarylhydrazine 3 have been synthesized through the nucleophilic substitution reaction of 1 with imidazole and 1,2,4‐triazole, respectively. 2,2′‐Diaryl‐2H,2′H‐[4,4′]bi[[1,2,4]‐triazolyl]‐3,3′‐dione 4 was obtained from the cycloaddition of α‐chloroformylarylhydrazine hydrochloride 1 with 1,2,4‐triazole at 60 °C and in absence of n‐Bu₃N. The inducing factor for cycloaddition of 1 with 1,2,4‐triazole was ascertained as hydrogen ion by the formation of 4 from the reaction of 3 with hydrochloric acid. 4 was also acquired from the reaction of 3 with 1 and this could confirm the reaction route for cycloaddition of 1 with 1,2,4‐triazole. Some acylation reagents were applied to induce the cyclization reaction of 2 and 3.1 possessing chloroformyl group could induce the cyclization of 2 to give 2‐aryl‐4‐(2‐aryl‐4‐vinyl‐semicarbazide‐4‐yl)‐2,4‐dihydro‐[1,2,4]‐triazol‐3‐one 6. 7 was obtained from the cyclization of 2 induced by some acyl chlorides. Acetic acid anhydride like acetyl chloride also could react with 2 to produce 7D . 5‐Substituted‐3‐aryl‐3H‐[1,3,4]oxadiazol‐2‐one 8 was produced from the cyclization reaction of 3 induced by some acyl chlorides or acetic acid anhydride. The 1,2,4‐triazole group of 3 played a role as a leaving group in the course of cyclization reaction. This was confirmed by the same product 8 which was acquired from the reaction of 1 , possessing a better leaving group: Cl, with some acyl chlorides or acetic acid anhydride.     

Synthesis and evaluation of polyacrylamides derived from polycyclic pendant naphthalene,indole, and phenothiazine based chalcone moiety as potent antimicrobial agents

Polycyclic chalcone‐containing polyacrylamides, namely, poly ((N‐(4‐((E)‐3‐(naphthalen‐6‐yl)‐3‐oxoprop‐1‐enyl) phenyl) acrylamide), poly((N‐(4‐((E)‐3‐(1H‐indol‐3‐yl)‐3‐oxoprop‐1‐enyl) phenyl) acrylamide), and poly((N‐(4‐((E)‐3‐oxo‐3‐(10H‐phenothiazin‐8‐yl) prop‐1‐enyl) phenyl) acrylamide), were synthesized by Claisen–Schmidt condensation reaction, followed by ultrasonic irradiation reduction. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, and ¹³C nuclear magnetic resonance spectroscopic technique. The newly synthesized polymers have been screened for antibacterial and antifungal activities by using resazurin reduction assay method, and the resulting polyacrylamides showed promising activity against various tested bacteria and fungi. Among the polymers, poly((N‐(4‐((E)‐3‐oxo‐3‐(10H‐phenothiazin‐8‐yl) prop‐1‐enyl) phenyl) acrylamide) and poly((N‐(4‐((E)‐3‐(1H‐indol‐3‐yl)‐3‐oxoprop‐1‐enyl) phenyl) acrylamide) exhibited better antifungal and antibacterial activities than poly ((N‐(4‐((E)‐3‐(naphthalen‐6‐yl)‐3‐oxoprop‐1‐enyl) phenyl) acrylamide), whereas all the polymers do not show any sign of antibacterial and antifungal activity against Streptococcus faecalis and Candida glabrata. Copyright © 2016 John Wiley & Sons, Ltd.     

Cationic ring‐opening polymerization of novel 1,3‐dehydroadamantanes with various alkyl substituents: Synthesis of thermally stable poly(1,3‐adamantane)s

Cationic ring‐opening polymerizations of 5‐alkyl‐ or 5,7‐dialkyl‐1,3‐dehydroadamantanes, such as 5‐hexyl‐ ( 4 ), 5‐octyl‐ ( 5 ), 5‐butyl‐7‐isobutyl‐ ( 6 ), 5‐ethyl‐7‐hexyl‐ ( 7 ), and 5‐butyl‐7‐hexyl‐1,3‐dehydroadamantane ( 8 ), were carried out with super Brønsted acids, such as trifluoromethanesulfonic acid or trifluoromethanesulfonimide in CH₂Cl₂ or n‐heptane. The ring‐opening polymerizations of inverted carbon–carbon bonds in 4–8 proceeded to afford corresponding poly(1,3‐adamantane)s in good to quantitative yields. Poly( 4–8 )s possessing alkyl substituents were soluble in 1,2‐dichlorobenzene, although a nonsubstituted poly(1,3‐adamantane) was not soluble in any organic solvent. In particular, poly( 8 ) exhibited the highest molecular weight at around 7500 g mol^?1 and showed excellent solubility in common organic solvents, such as THF, CHCl₃, benzene, and hexane. The resulting poly( 4–8 )s containing adamantane‐1,3‐diyl linkages showed good thermal stability, and 10% weight loss temperatures (T₁₀) were observed over 400 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4111–4124     

Insertion Reactions of 1,2‐Disubstituted Olefins with an α‐Diimine Palladium(II) Complex

The migratory insertions of cis or trans olefins CH(X)?CH(Me) (X = Ph, Br, or Et) into the metal–acyl bond of the complex [Pd(Me)(CO)(ⁱPr₂dab)]⁺ [B{3,5‐(CF₃)₂C₆H₃}₄]^? ( 1 ) (ⁱPr₂dab = 1,4‐diisopropyl‐1,4‐diazabuta‐1,3‐diene = N,N′‐(ethane‐1,2‐diylidene)bis[1‐methylethanamine]) are described (Scheme 1). The resulting five‐membered palladacycles were characterized by NMR spectroscopy and X‐ray analysis. Experimental data reveal some important aspects concerning the regio‐ and stereochemistry of the insertion process. In particular, the presence of a Ph or Br substituent at the alkene leads to the formation of highly regiospecific products. Moreover, in all cases, the geometry of the substituents in the formed palladacycle was the same as in the starting olefin, as a consequence of a cis addition of the Pd–acyl fragment to the C?C bond. Reaction with CO and MeOH of the five‐membered complex derived from trans‐β‐methylstyrene (= [(1E)‐prop‐1‐enyl]benzene) insertion, yielded the 2,3‐substituted γ‐keto ester 9 with an (2RS,3SR)‐configuration (Scheme 3).     

New Long‐Chain Esters and Adenine Analogs from the Leaves of Formosan Bridelia balansae

Six new compounds, including the two long‐chain esters balansenate I (=6,8,11‐trimethyldodecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 1 ) and balansenate II (=10,12,15‐trimethylhexadedecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 2 ), the eburicane‐like triterpenoid bridelone (=hexadecahydro‐4,4,10,13,14‐pentamethyl‐17‐(5‐methyl‐1,4‐dimethylenehexyl)‐3H‐cyclopenta[a]phenanthren‐3‐one; 3 ), the ‘deimino‐xanthine', bridelonine (=5‐(3‐methylbut‐2‐enyl)pyrrolo[3,4‐d]imidazole‐4,6(1H,5H)‐dione; 6 ), and the two adenine analogs 9‐(3‐methylbut‐2‐enyl)adenine ( 7 ) and 1‐(3‐methylbut‐2‐enyl)adenine ( 8 ), besides three known compounds, i.e., N⁶‐(3‐methylbut‐2‐enyl)adenine ( 4 ), 3‐(3‐methylbut‐2‐enyl)adenine ( 5 ), and adenine ( 9 ), were isolated from the leaves of Formosan Bridelia balansae. The novel skeleton of 6 consists of a fused pyrrolidine‐2,5‐dione and imidazole moiety. The already known adenines 7 and 8 were isolated for the first time from a plant. The structures of the isolated compounds were elucidated by spectroscopic analyses.     

Chiral sensing of Eu(III)‐containing achiral polymer complex from chiral amino acids coordination induction

The β‐diketonate‐based achiral polymer P‐1 could be synthesized by the polymerization of 3,7‐dibromo‐2,8‐dimethoxy‐5,5‐dioctyl‐5H‐dibenzo[b,d]silole ( M1 ) with (Z)?1,3‐bis(4‐ethynylphenyl)?3‐hydroxyprop‐en‐1‐one ( M2 ) via typical Sonogashira coupling reaction. The β‐diketonate unit in the main chain backbone of P‐1 can further coordinate with Eu(TTA)_x [TTA^? = 4,4,4‐trifluoro‐1‐(thiophen‐2‐yl)butane‐1,3‐dionate anion, X = 1, 2, 3] to afford corresponding Eu(III)‐containing polymer complexes. The resulting achiral polymer complex P‐2 (X = 2) can exhibit strong circular dichroism (CD) response toward both N‐Boc‐l and d‐ proline enantiomers. The CD signal was preliminarily attributed to coordination induction between chiral N‐Boc‐proline and the Eu(III) complex moiety. The linear regression analysis of CD sensing shows a good agreement between the magnitude of molar ellipticity and concentration of chiral N‐Boc‐l or d‐ proline, which indicates this kind Eu(III)‐containing achiral polymer complex can be used as a chiral probe for enantioselective recognition of N‐Boc‐l or d‐ proline enantiomers based on Cotton effect of CD spectra. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3080–3086     

Reaction of 3‐Hydroxyquinoline‐2,4‐diones with Inorganic Thiocyanates in the Presence of Ammonium or Alkylammonium Ions: the Unexpected Replacement of a Hydroxy Group by an Amino Group

3‐Hydroxyquinoline‐2,4‐diones react with KSCN in the presence of the NH$\rm{{_{4}^{+}}}$ ions to generate 2,3‐dihydro‐3‐thioxoimidazo[1,5‐c]quinazolin‐5(6H)‐ones, 2,3‐dihydro‐2‐thioxo‐1H‐imidazo[4,5‐c]quinolin‐4(5H)‐ones, and products of molecular rearrangement of the 3‐aminoquinolinedione intermediates. Starting compounds with a benzyl (Bn) group at C(3) afford 3‐aminoquinolinediones, even when only AcONH₄ is used. The results of the reaction between 3‐hydroxyquinoline‐2,4‐diones and KSCN in the presence of BuNH₂ show that replacing a OH group with a secondary NH₂ group is also possible.     

HP‐CsB5O8: Synthesis and Characterization of an Outstanding Borate Exhibiting the Simultaneous Linkage of All Structural Units of Borates

The new cesium pentaborate HP‐CsB₅O₈ is synthesized under high‐pressure/high‐temperature conditions of 6 GPa and 900 °C in a Walker‐type multianvil apparatus. The compound crystallizes in the orthorhombic space group Pnma (Z=4) with the parameters a=789.7(1), b=961.2(1), c=836.3(1) pm, V=0.6348(1) nm³, R₁=0.0359 and wR₂=0.0440 (all data). The new structure type of HP‐CsB₅O₈ exhibits the simultaneous linkage of trigonal BO₃ groups, corner‐sharing BO₄ tetrahedra, and edge‐sharing BO₄ tetrahedra including the presence of threefold‐coordinated oxygen atoms. With respect to the rich structural chemistry of borates, HP‐CsB₅O₈ is the second structure type possessing this outstanding combination of the main structural units of borates in one compound. The structure consists of corrugated chains of corner‐ and edge‐sharing BO₄ tetrahedra interconnected through BO₃ groups forming octagonal channels. Inside these channels, cesium is 13+3‐fold coordinated by oxygen atoms. ¹¹B MQMAS NMR spectra are analyzed to estimate the isotropic chemical shift values and quadrupolar parameters. IR and Raman spectra are obtained and compared to the calculated vibrational frequencies at the Γ‐point. The high‐temperature behavior is examined by means of temperature‐programmed powder diffraction.