Regioselective quinazoline C2 modifications through the azide-tetrazole tautomeric equilibrium.

2-Chloro-4-sulfonylquinazolines undergo functional group swap when treated with an azide nucleophile: 1) the azide replaces the sulfonyl group at the C4 position; 2) the intrinsic azide-tetrazole tautomeric equilibrium directs the nucleofugal sulfinate from the first step to replace chloride at the C2 position. This transformation is effective with quinazolines bearing electron-rich substituents. Therefore, the title transformations are demonstrated on the 6,7-dimethoxyquinazoline core, which is present in pharmaceutically active substances. The methodology application is showcased by transforming the obtained 4-azido-6,7-dimethoxy-2-sulfonylquinazolines into the α1-adrenoceptor blockers terazosin and prazosin by further C2-selective SNAr reaction and azide reduction.

Never-Ending Story: New Cyclodextrin-Based Metal-Organic Framework Crystal Structures Obtained Using Different Crystallization Methods.

Six novel cyclodextrin (CD)-based metal-organic frameworks (MOFs) were synthesized using distinct crystallization methodologies. A modified vapor diffusion method is introduced for the first time, termed fast crystallization, which enables the rapid solid-state formation of MOF compounds. This innovative method yielded four of the newly synthesized MOFs. The crystal structures of five obtained frameworks were structurally characterized through single-crystal X-ray diffraction, while one, compound 5 (γ-CD-K-5), was additionally characterized as a bulk powder. Structural analysis revealed that two of the newly obtained MOFs, namely, compound 2 (α-CD-K-2) and compound 3 (α-CD-Rb-3), exhibited isostructural characteristics, forming a three-dimensional (3D) framework. Compound 1 (α-CD-K-1) shared the same space group as EVEGET (α-CD-K) and displayed the same framework type. Furthermore, the crystal packing of compound 4 (ß-CD-K-4) closely resembled that of compound 1 and EVEGET, with the only distinction lying in the type of CD employed. Notably, compound 6 (γ-CD-K-6) incorporated an iodine ion with an occupancy of 0.2. To discern the intermolecular interactions within the obtained MOFs, the Hirshfeld surface was calculated using Crystal Explorer software.

1,2-Silyl Shift-Induced Heterocyclization of Propargyl Silanes: Synthesis of Five-Membered Heterocycles Containing a Functionalized Olefin Side Chain.

Propargyl silanes with a terminal alkyne moiety undergo a 1,2-silyl shift when activated with electrophiles such as H+, Br+, I+, and PhSe+. A method was developed to trap 1,3-transposed electrophilic centers with various internal O-, N-, and S-nucleophiles in a 5-exo manner. This synthetic procedure provided five-membered heterocycles containing a trisubstituted olefin side chain. The scope of the method includes access to tetrahydrofuran, γ-butyrolactone, 2-isooxazoline, pyrrolidine, and thiolane derivatives in yields ranging from 25 to 85% (23 examples in total). Reactions with TsNBr2 ensured complete (E)-selectivity of the newly formed olefins. Further functionalization of the obtained 1-trialkylsilyl-2-bromovinyl side chain was demonstrated by double-bond geometry-preserving electrophilic substitution and cross-coupling reactions that provided heterocycles with a trisubstituted vinyl moiety.

1,3-Difunctionalization of Propargyl Silanes with Concomitant 1,2-Silyl Shift: Synthesis of Allyl Functionalized Vinyl Silanes.

Terminal alkynes with a silyl group at the propargylic position upon activation with electrophiles such as N-bromosuccinimide undergo (E)-selective 1,2-silyl group migration. Subsequently, an allyl cation is formed that is intercepted by an external nucleophile. This approach provides allyl ethers and esters with stereochemically defined vinyl halide and silane handles for further functionalization. The scope of propargyl silanes and electrophile-nucleophile pairs are investigated, and various trisubstituted olefins are prepared in up to 78% yield. The obtained products have been demonstrated to serve as building blocks for transition-metal-catalyzed cross-couplings of vinyl halides, silicon-halogen exchange, and allyl acetate functionalization reactions.

SnAr Reactions of 2,4-Diazidopyrido[3,2-d]pyrimidine and Azide-Tetrazole Equilibrium Studies of the Obtained 5-Substituted Tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines.

A straightforward method for the synthesis of 5-substituted tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines from 2,4-diazidopyrido[3,2-d]pyrimidine in SnAr reactions with N-, O-, and S- nucleophiles has been developed. The various N- and S-substituted products were obtained with yields from 47% to 98%, but the substitution with O-nucleophiles gave lower yields (20-32%). Furthermore, the fused tetrazolo[1,5-a]pyrimidine derivatives can be regarded as 2-azidopyrimidines and functionalized in copper(I)-catalyzed azide-alkyne dipolar cycloaddition (CuAAC) and Staudinger reactions due to the presence of a sufficient concentration of the reactive azide tautomer in solution. In total, seven products were fully characterized by their single crystal X-ray studies, while five of them were representatives of the tetrazolo[1,5-a]pyrido[2,3-e]pyrimidine heterocyclic system. Equilibrium constants and thermodynamic values were determined using variable temperature 1H NMR and are in agreement of favoring the tetrazole tautomeric form (ΔG298 = -3.33 to -7.52 (kJ/mol), ΔH = -19.92 to -48.02 (kJ/mol) and ΔS = -43.74 to -143.27 (J/mol·K)). The key starting material 2,4-diazidopyrido[3,2-d]pyrimidine presents a high degree of tautomerization in different solvents.

Combined Use of Structure Analysis, Studies of Molecular Association in Solution, and Molecular Modelling to Understand the Different Propensities of Dihydroxybenzoic Acids to Form Solid Phases.

The arrangement of hydroxyl groups in the benzene ring has a significant effect on the propensity of dihydroxybenzoic acids (diOHBAs) to form different solid phases when crystallized from solution. All six diOHBAs were categorized into distinctive groups according to the solid phases obtained when crystallized from selected solvents. A combined study using crystal structure and molecule electrostatic potential surface analysis, as well as an exploration of molecular association in solution using spectroscopic methods and molecular dynamics simulations were used to determine the possible mechanism of how the location of the phenolic hydroxyl groups affect the diversity of solid phases formed by the diOHBAs. The crystal structure analysis showed that classical carboxylic acid homodimers and ring-like hydrogen bond motifs consisting of six diOHBA molecules are prominently present in almost all analyzed crystal structures. Both experimental spectroscopic investigations and molecular dynamics simulations indicated that the extent of intramolecular bonding between carboxyl and hydroxyl groups in solution has the most significant impact on the solid phases formed by the diOHBAs. Additionally, the extent of hydrogen bonding with solvent molecules and the mean lifetime of solute-solvent associates formed by diOHBAs and 2-propanol were also investigated.

1,2,3-Triazoles as leaving groups in SNAr-Arbuzov reactions: synthesis of C6-phosphonated purine derivatives.

A new method for C-N bond transformations into C-P bonds was developed using 1,2,3-triazoles as leaving groups in SNAr-Arbuzov reactions. A series of C6-phosphonated 2-triazolylpurine derivatives was synthesized for the first time, with the isolated yields reaching up to 82% in the C-P-bond-forming event. The SNAr-Arbuzov reaction of 2,6-bistriazolylpurines follows the general regioselectivity pattern of the C6-position being more reactive towards substitution, which was unambiguously proved by X-ray analysis of diethyl (9-heptyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-yl)phosphonate.

A Concise Bioinspired Semisynthesis of Rumphellaones A-C and Their C-8 Epimers from ß-Caryophyllene.

The first semisynthetic route toward rumphellaones B (2) and C (3) and their C-8 epimers as well as the shortest synthesis of rumphellaone A (1) and its C-8 epimer from the most accessible sesquiterpene, ß-caryophyllene (4), is presented. Synthetic routes involved caryophyllonic acid as a key intermediate, which was converted to rumphellaone A (and epimer) via acid-catalyzed lactonization and rumphellaone C (and epimer) using one-pot epoxidation-lactonization. Rumphellaone B (2) and its epimer were obtained from rumphellaone A (1) and its epimer, respectively, using Saegusa-Ito oxidation. The absolute configuration at C-8 was confirmed by single-crystal X-ray analysis of rumphellaone B (2) and an acylated derivative of rumphellaone C.

Crystal structure of a two-dimensional metal-organic framework assembled from lithium(I) and γ-cyclo-dextrin.

The crystal structure of the polymeric title compound, catena-poly[[[di-aqua-lithium]-µ-γ-cyclo-dextrin(1-)-[aqua-lithium]-µ-γ-cyclo-dextrin(1-)] pentadecahydrate], {[Li2(C48H79O40)2(H2O)3]·15H2O} n , consists of deprotonated γ-cyclo-dextrin (CD) mol-ecules assembled by lithium ions into metal-organic ribbons that are cross-linked by multiple O-H⋯O hydrogen bonds into sheets extending parallel to (01). Within a ribbon, one Li+ ion is coordinated by one deprotonated hydroxyl group of the first γ-CD torus and by one hydroxyl group of the second γ-CD torus as well as by two water mol-ecules. The other Li+ ion is coordinated by one deprotonated hydroxyl and by one hydroxyl group of the second γ-CD torus, by one hydroxyl group of the first γ-CD torus as well as by one water mol-ecule. The coordination spheres of both Li+ cations are distorted tetra-hedral. The packing of the structure constitute channels along the a axis. Parts of the hy-droxy-methyl groups in cyclo-dextrin molecules as well as water mol-ecules show two-component disorder. Electron density associated with additional disordered solvent mol-ecules inside the cavities was removed with the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] routine in PLATON. These solvent mol-ecules are not considered in the given chemical formula and other crystal data. Five out of the sixteen hy-droxy-methyl groups and one water mol-ecule are disordered over two sets of sites.

Sulfonyl Group Dance: A Tool for the Synthesis of 6-Azido-2-sulfonylpurine Derivatives.

9-Substituted 2-chloro-6-sulfonylpurines provide 6-azido-2-sulfonylpurine derivatives with 61-83% yields when treated with sodium azide. Under optimized reaction conditions, the title compounds are obtained in a one-pot process, which involves a sequential treatment of 2,6-dichloropurines with a selected sodium sulfinate and sodium azide. Such a sulfonyl group dance (functional group swap) results from a cascade of SNAr reactions, which are facilitated by azidoazomethine-tetrazole (azide-tetrazole) tautomeric equilibrium. The formation of Meisenheimer-type intermediates as tetrazolopurine tautomers was supported by various spectroscopic methods, including 15N NMR.

Johnson-Corey-Chaykovsky fluorocyclopropanation of double activated alkenes: scope and limitations.

Johnson-Corey-Chaykovsky fluorocyclopropanation of double activated alkenes utilizing S-monofluoromethyl-S-phenyl-2,3,4,5-tetramethylphenylsulfonium tetrafluoroborate is an efficient approach to obtain a range of monofluorocyclopropane derivatives. So far, fluoromethylsulfonium salts have displayed the broadest scope for direct fluoromethylene transfer. In contrast to more commonly used fluorohalomethanes or freon derivatives, diarylfluoromethylsulfonium salts are bench stable, easy-to use reagents useful for the direct transfer of a fluoromethylene group to alkenes giving access to the challenging products - fluorocyclopropane derivatives. Interplay between the reactivity of the starting materials and stability of the fluorocyclopropanes formed determines the outcome of the process.

Brønsted Acid Catalyzed 1,2-Silyl Shift in Propargyl Silanes: Synthesis of Silyl Dienes and Silyl Indenes.

A general method for generation of allyl carbenium ions from propargyl silanes via a 1,2-silyl shift by Brønsted acids is reported. Two possible reaction pathways are described. Deprotonation results in silyl dienes with yields from 52% to 92%. Intramolecular Friedel-Crafts reactions of aryl-substituted systems give access to silyl indenes with yields of 18-90% depending on the substitution pattern. The obtained products have been shown to react as alkenyl silanes in Hiyama coupling and electrophilic substitution and as dienes in Diels-Alder cycloaddition.

Crystal structure and metabolic activity of 4-(thien-2-yl)-2-methyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carb-oxy-lic acid eth-oxy-carbonyl-phenyl-methyl-ester.

In the title compound, C25H25NO5S, which exhibits metabolism-regulating activity, the 1,4-di-hydro-pyridine ring adopts a flattened boat conformation while the cyclo-hexenone ring is in an envelope conformation. Mol-ecules in the crystal are assembled into C(6) chains along the a-axis direction via N-H⋯O hydrogen bonds. The thienyl fragment is disordered over two sets of sites in a 0.7220 (19):0.2780 (19) ratio.

Crystal structure of 3-hy-droxy-2-(4-hy-droxy-3-meth-oxy-phenyl-methyl)-5,5-di-methyl-cyclo-hex-2-enone.

In the title compound, C16H20O4, a new starting compound for the synthesis of various heterocycles, the partially saturated six-membered ring adopts a sofa conformation. An intra-molecular O-H⋯O hydrogen bond is observed in the guaiacol residue. In the crystal, mol-ecules are assembled into a sheet structure parallel to the ab plane via O-H⋯O hydrogen bonds. The hydrogen-bond pattern is described by an R44(28) graph-set motif. The sheets are further linked by C-H⋯O hydrogen bonds into a three-dimensional network.

Crystal structure of 3,6,6-trimethyl-4-oxo-1-(pyridin-2-yl)-4,5,6,7-tetra-hydro-1H-indazol-7-aminium chloride and its monohydrate.

The title compounds, C15H19N4O+·Cl- and C15H19N4O+·Cl-·H2O, obtained in attempts to synthesize metal complexes using tetra-hydro-indazole as a ligand, were characterized by NMR, IR and X-ray diffraction techniques. The partially saturated ring in the tetra-hydro-indazole core adopts a sofa conformation. An intra-molecular N-H⋯N hydrogen bond formed by the protonated amino group and the N atom of the pyridyl substituent is found in the first structure. In the hydro-chloride, the organic moieties are linked by two N-H⋯Cl- hydrogen bonds, forming a C(4) graph-set. In the hydrate crystal, a Cl- anion and a water mol-ecule assemble the moieties into infinite bands showing hydrogen-bond patterns with graph sets C(6), R64(12) and R42(8). Organic moieties form π-π stacked supra-molecular structures running along the b axis in both structures.

Structural characterization of cevimeline and its trans-impurity by single crystal XRD.

Cevimeline is muscarinic receptor agonist which increases secretion of exocrine glands. Cevimeline base is a liquid (m.p. 20-25 °C) at ambient conditions, therefore its pharmaceutical formulation as a solid hydrochloride hemihydrate has been developed. The synthesis of cevimeline yields its cis- and trans-isomers and only the cis-isomer is recognized as the API and used in the finished formulation. In this study structural and physicochemical investigations of hydrochloride hemihydrates of cis- and trans-cevimelines have been performed. Single crystal X-ray analyses of both cis- and trans-isomers of cevimeline are reported here for the first time. It was found that the cis-isomer, the API, has less dense crystal packing, lower melting point and higher solubility in comparison to the trans-isomer.

Zwitterionic and free forms of arylmethyl Meldrum's acids.

C-Alkyl (including C-arylmethyl) derivatives of Meldrum's acids are attractive building blocks in organic synthesis, mainly due to the unusually high acidity of the resulting compounds. Three examples, namely 5-[4-(diethylamino)benzyl]-2,2-dimethyl-1,3-dioxane-4,6-dione, C17H23NO4, (I), 2,2-dimethyl-5-(2,4,6-trimethoxybenzyl)-1,3-dioxane-4,6-dione, C16H20O7, (II), and 5-(4-hydroxy-3,5-dimethoxybenzyl)-2,2-dimethyl-1,3-dioxane-4,6-dione, C15H18O7, (III), have been synthesized, characterized by NMR and IR spectroscopy, and studied by single-crystal X-ray structure analysis. The nature of the different substituents resulted in remarkable differences in both the molecular conformations and the crystal packing arrangements. The presence of a substituent with a basic centre in compound (I) leads to the formation of an inner salt accompanied by drastic changes in the conformation of the 1,3-dioxane-4,6-dione fragment. By virtue of strong N-H···O hydrogen bonds, the residues are assembled into infinite chains with the graph-set descriptor C(10). Compound (II) contains methoxy groups in both the ortho- and para-positions of the arylmethyl fragment. Because of the absence of classical hydrogen-bond donors in this structure, the crystal packing is controlled by van der Waals forces and weak C-H···O interactions. Compound (III) contains methoxy groups in both meta-positions and a hydroxy group in the para-position. Supramolecular tetrameric synthons which comprise hydrogen-bonded dimers associated into tetramers through π-π interactions of overlapping benzene rings were observed.

Crystal structure of 3-amino-5,5-dimethyl-2-[(E)-2-nitro-ethen-yl]cyclo-hex-2-en-1-one.

The asymmetric unit of the title compound, C10H14N2O3, contains two independent mol-ecules with similar conformations. In the both mol-ecules, the cyclo-hexene rings adopt the same envelope conformation with the flap C atoms lying 0.658 (3) and 0.668 (3) Šfrom the mean planes formed by the remaining atoms. In the crystal, adjacent mol-ecules are connected via N-H⋯O hydrogen bonds and weak C-H⋯O inter-actions, forming supra-molecular layers parallel to (-101).

Betulin 3,28-di-O-tosyl-ate.

The title compound, C44H62O6S2 {systematic name: (1R,3aS,5aR,5bR,7aR,9S,11aR,11bR,13aR,13bR)-5a,5b,8,8,11a-penta-methyl-1-(prop-1-en-2-yl)-3a-[(tos-yloxy)meth-yl]icosa-hydro-1H-cyclo-penta-[a]chrysen-9-yl 4-methyl-benzene-sulfonate}, was obtained by tosyl-ation of naturally occurring betulin. All the cyclo-hexane rings adopt chair conformations and the cyclo-pentane ring adopts a twisted envelope conformation, with the C atom bearing the tosyl-methyl substituent forming the flap. In the crystal, mol-ecules form a three-dimensional network through multiple weak C-H⋯O hydrogen bonds.

{(3aR,5S,6R,6aR)-5-[(R)-1,2-Di-hydroxy-eth-yl]-2,2-di-methyl-tetra-hydro-furo[2,3-d][1,3]dioxol-6-yl}methyl methane-sulfonate.

In the title compound, C11H20O8S, the furan-ose ring has a pseudorotation phase angle equal to 31.3° and assumes a (3) T 4 conformation, with deviations of 0.297 (4) and -0.152 (4) Šfor the corresponding C atoms. The dioxolane ring adopts an envelope conformation. One of the O atoms is at the flap and deviates from the least-squares plane formed by the other four ring atoms by 0.405 (2) Å. The dihedral angle between the planar fragments of the rings is 63.53 (8)°. In the crystal, mol-ecules are associated into sheets perpendiculer to the b axis by means of O-H⋯O hydrogen bonds. A few weak C-H⋯O inter-actions are also observed.