Organophotocatalytic Remote Thiocyanation Reaction via Ring-Opening Functionalization of Cycloalkanols.

The remote C(sp3)-SCN bond formation via ring-opening functionalization of cycloalkanols with N-thiocyanatosaccharin as the precursor of SCN radicals and pyrylium salt as the organic photocatalyst under visible light has been developed. Thus, various terminal keto thiocyanates were prepared without transition metals and oxidants in moderate to good yields. The simplicity, wide substrate scope and mild conditions feature its synthetic application capability.

Me3SiBr-promoted cascade electrophilic thiocyanation/cyclization of ortho-alkynylanilines to synthesize indole derivatives.

A Lewis acid-promoted electrophilic thiocyanation/cyclization of ortho-alkynylanilines for the synthesis of indole derivatives has been developed. The reaction utilizes Me3SiBr as the Lewis acid and N-thiocyanatosuccinimide as the thiocyanation reagent. A series of 2-aryl-3-thiocyanato indoles were prepared in moderate to high yields under mild conditions without metals and oxidants. It provides an efficient protocol for the construction of the indole skeleton and C-SCN and C-N bonds in one step as well.

Copper(I)-catalyzed electrophilic thiocyanation/dearomatization/spirocyclization of benzofurans to synthesize benzannulated spiroketals.

A Lewis acid-catalyzed electrophilic dearomatizative thiocyanation and cyclization of benzofurans with N-thiocyanatosuccinimide has been accomplished by Lewis acid catalysis with CuOTf under mild conditions. It was suggested that the electrophilic thiocyanating reagent was activated by CuOTf, and difunctionalization was achieved through a thiocyanation/spirocyclization pathway. Thus, a series of thiocyanato-containing spiroketals were obtained in moderate to high yields. It provides an alternative approach for the synthesis of functionalized [6,5]/[5,5]-spiroketals.

Synthesis of thiocyanato-containing phenanthrenes and dihydronaphthalenes via Lewis acid-activated tandem electrophilic thiocyanation/carbocyclization of alkynes.

A tandem electrophilic thiocyanation and cyclization of arene-alkynes has been developed under mild conditions, affording thiocyanato-substituted phenanthrenes, dihydronaphthalenes, 2H-chromenes and dihydroquinolines in moderate to excellent yields. This reaction provides an efficient protocol for the construction of C-SCN and C-C bonds in one step. In this transformation, N-thiocyanato reagent serves as a convenient precursor to transfer SCN+ in the presence of trimethylchlorosilane, and the cyclization exhibited exclusive 6-endo-dig selectivity. Finally, a gram scale reaction and further derivatizations highlight the utility of this synthetic strategy.

Electrophilic Thiocyanato Reagent Assisted Oxa-Michael/Thiocyanation of α,ß-Unsaturated Ketones.

A route for thiocyanation-functionalization of the electron-deficient C═C double bond was developed. Regioselective thiocyanation-etherification of α,ß-unsaturated ketones was achieved. The desired products were obtained in moderate to high yields under mild conditions. It was suggested that the nucleophile was activated by the electrophilic thiocyanato reagent, and difunctionalization was achieved through a 1,4-addition/thiocyanation pathway.

Atom-Economical Thiocyanation-Amination of Alkynes with N-Thiocyanato-Dibenzenesulfonimide.

A highly regioselective protocol for intermolecular thiocyanation-amination of alkynes by N-thiocyano-dibenzenesulfonimide (NTSI) as the SCN and nitrogen sources has been developed. A C-S bond and C-N bond are simultaneously constructed in only one step. The reaction under simple mild conditions features a broad substrate scope, atom economy, high yields (up to 94%), and excellent functional group tolerance.

Lewis Acid-Catalyzed Asymmetric Selenocyanation of ß-Ketoesters with N-Selenocyanatosaccharin.

The first electrophilic asymmetric selenocyanation has been achieved in the presence of Ni(OTf)2 and (R,R)-DBFOX/Ph using N-selenocyanatosaccharin as the new selenocyanation reagent. Thus, a series of α-selenocyanato-ß-keto esters were synthesized with high yields (up to 99%) and good ee values (up to 92% ee). The readily preparation of the reagent and high enantioselectivity make this methodology much practical for the synthesis of chiral selenocyanates.

Organocatalyzed Asymmetric α-Thiocyanation of Oxindoles: Synthesis of Chiral Tertiary 3-Thiocyanatoxindoles.

An enantioselective thiocyanation of oxindoles has been developed for the first time using a bifunctional cinchona-derived organo-catalyst and N-thiocyanatophthalimide as the electrophilic thiocyanation source in the presence of 2-naphthol as the additive. Various enantioenriched 3,3'-disubstituted oxindoles with SCN-containing quaternary carbon stereocenters were synthesized under mild conditions in high yields (up to 99%) and good enantioselectivities (up to 6:94 er).

N-Thiocyanato-dibenzenesulfonimide: a new electrophilic thiocyanating reagent with enhanced reactivity.

A novel electrophilic thiocyanating reagent, N-thiocyanato-dibenzenesulfonimide, was prepared and exhibited enhanced electrophilicity with a wide scope of substrates. Thus, it reacted with activated aromatics such as phenols, indoles, anilines and anisoles without a catalyst giving the corresponding thicyanate derivatives in high yields, while TfOH for unactivated arenes and hetero aromatics and Zn(OTf)2 for ketones was used as the catalyst, respectively. It is noteworthy that internal alkenes and styrenes were bifunctionalized giving 1,2-amino thiocyanates in high yields.

N-Thiocyanatosaccharin: A "Sweet" Electrophilic Thiocyanation Reagent and the Synthetic Applications.

N-Thiocyanatosaccharin (R1) was readily prepared from the sweet additive Saccharin in two steps with a 71% overall yield. By applying this new reagent to diverse nucleophiles such as benzothiophenes, indoles, oxindoles, aromatic amines, phenols, ß-keto carbonyl compounds, and aromatic ketones, a novel electrophilic thiocyanation reaction was achieved with high yields (up to 99%). The potential recycling of Saccharin, the wide scope of substrates, and the mild reaction conditions made this protocol much more practical.

Highly Enantioselective α-Cyanation with 4-Acetylphenyl Cyanate.

A highly effective asymmetric version of α-cyanation of ß-keto esters and amides was developed with a Lewis-acid catalyst. Thus, by using 10 mol % of a tridentate bisoxazoline-zinc(II) complex as the catalyst, a series of chiral nitriles containing a quaternary carbon center were obtained in excellent enantioselectivities (up to 97 % enantiomeric excess) and up to 95 % yield in the presence of 4 Šmolar sieve at room temperature. For the first time, mild and active 4-acetylphenyl cyanate was used instead of cyano-hyperiodinate as the cationic cyano source for catalytic asymmetric α-cyanation.

Enantioselective electrophilic cyanation of ß-keto amides catalysed by a cinchona organocatalyst.

An operationally simple protocol for the enantioselective electrophilic α-cyanation of ß-keto amides catalyzed by cinchona-derived catalysts has been demonstrated. The resulting products could be obtained with good to high enantioselectivities (up to 88% ee) and with excellent yields (up to 94%) by employing the mild active 4-acetylphenyl cyanate as the cationic cyano source in the catalytic asymmetric α-cyanation reaction.

The direct electrophilic cyanation of ß-keto esters and amides with cyano benziodoxole.

The direct electrophilic α-cyanation of ß-keto esters and amides has been developed using a hypervalent iodine benziodoxole-derived cyano reagent. The procedure is accomplished within 10 min and without the use of any catalyst in DMF, at room temperature. Thus, the highly functionalized quaternary carbon-centered nitriles were produced in high to excellent yields.

Construction and Modification of Nitrogen-Rich Polycyclic Frameworks: A Promising Fused Tricyclic Host-Guest Energetic Material with Heat Resistance, High Energy, and Low Sensitivity.

The construction and modification of novel energetic frameworks to achieve an ideal balance between high energy density and good stability are a continuous pursuit for researchers. In this work, a fused [5,6,5]-tricyclic framework was utilized as the energetic host to encapsulate the oxidant molecules for the first time. A series of new pyridazine-based [5,6] and [5,6,5] fused polycyclic nitrogen-rich skeletons and their derivatives were designed and synthesized. Two strategies, amino oxidation and host-guest inclusion, were used to modify the skeleton in only one step. All compounds exhibit good comprehensive properties (Td (onset) > 200 °C, ρ > 1.85 g cm-3, Dv > 8400 m s-1, IS > 20 J, FS > 360 N). Benefiting from the pyridazine-based fused tricyclic structure with more hydrogen bonding units and larger conjugated systems, the first example of [5,6,5]-tricyclic host-guest energetic material triamino-9H-pyrazolo[3,4-d][1,2,4]triazolo[4,3-b]pyridazine-diperchloric acid (10), shows high decomposition temperature (Td (onset) = 336 °C), high density and heats of formation (ρ = 1.94 g cm-3, ΔHf = 733.4 kJ mol-1), high detonation performance (Dv = 8820 m s-1, P = 36.2 GPa), high specific impulse (Isp = 269 s), and low sensitivity (IS = 30 J, FS > 360 N). The comprehensive performance of 10 is superior to that of high-energy explosive RDX and heat-resistant explosives such as HNS and LLM-105. 10 has the potential to become a comprehensive advanced energetic material that simultaneously satisfies the requirements of high-energy and low-sensitivity explosives, heat-resistant explosives, and solid propellants. This work may give new insights into the construction and modification of a nitrogen-rich polycyclic framework and broaden the applications of fused polycyclic framework for the development of host-guest energetic materials.

7-Iodo-3,3-diphenyl-octa-hydro-benzo-furan.

The title compound, C20H21IO, was synthesized by cyclo-haloetherification of 2-(cyclo-hex-2-en-yl)-2,2-diphenyl-ethanol in CH2Cl2, and crystallized with two independent mol-ecules in the asymmetric unit. The six-membered cyclo-hexane ring adopts a chair conformation, while the five-membered ring adopts an envelope conformation with the fused C atom opposite the O atom as the flap in each case [displacements of the flap atoms = 0.6813 (3) and 0.6679 (3) Å]. In the crystal, mol-ecules are linked via pairs of C-H⋯π inter-actions, forming inversion dimers.

Synthesis and characterization of energetic 3-nitro-1,2,4-oxadiazoles.

All new: 3-Nitro-5-guanidino-1,2,4-oxadiazole (NOG) was synthesized from diaminoglycoluril with in situ generated dimethyldioxirane (DMDO). The impact sensitivity of NOG is more than 40 J with a decomposition temperature of 290 °C. Some other energetic derivatives have been prepared and characterized.

Asymmetric trifluoromethylation of aromatic aldehydes by cooperative catalysis with (IPr)CuF and quinidine-derived quaternary ammonium salt.

A general enantioselective trifluoromethylation of aldehydes has been developed using (IPr)CuF and quinidine-derived quaternary ammonium salt as the cooperative catalyst. Thus, a wide range of aromatic aldehydes have been converted to the corresponding products in up to 92% yield and 81% ee at 2 mol% of catalyst loading. The greatly enhanced activity and enantioselectivity result from the initiative generation of active [(IPr)CuCF(3)] as well as additional coordination activation of other copper species.

AIBN-initiated direct thiocyanation of benzylic sp3 C-H with N-thiocyanatosaccharin.

Direct thiocyanations of benzylic compounds have been implemented. Here, a new strategy, involving a free radical reaction pathway initiated by AIBN, was used to construct the benzylic sp3 C-SCN bond. In this way, the disadvantage of other strategies involving introducing leaving groups in advance to synthesize benzyl thiocyanate compounds was overcome. The currently developed protocol also involved the use of readily available raw materials and resulted in high product yields (up to 100%), both being great advantages for synthesizing benzyl thiocyanates.

Tuning the chiral environment of C2-symmetric diene ligands: development of 3,7-disubstituted bicyclo[3.3.1]nona-2,6-dienes.

Through the structural analysis of bicyclo[3.3.1]nona-2,6-dienes, new C(2)-symmetric chiral diene ligands 1 based on 3,7-disubstituted bicyclo[3.3.1]nona-2,6-diene framework have been designed and synthesized. These chiral ligands readily bind to rhodium(I) and provide a different chiral environment from the existing chiral dienes. The rhodium complexes thus obtained act as effective catalysts for 1,4-addition of alkenyl- and arylboronic acids to various alpha,beta-unsaturated ketones, including several combinations that were previously difficult to provide high enantioselectivity.

The Chemistry and Properties of Energetic Materials Bearing [1,2,4]Triazolo[4,3-b][1,2,4,5]tetrazine Fused Rings.

Treatment of heterocyclic amines featuring fused rings of [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine with fuming HNO3 /P2 O5 leads to six fully characterized explosives through multiple nitration and reduction or oxidation mechanism. Thus, 4-nitro-N-(3-nitro[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-1,2,5-oxadiazol-3-amine (3 b, TTDNF) showed high performance (D=9180 m s-1 , P=36.7 GPa) and low impact sensitivity (IS>40 J) while N-([1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-3-nitro-1,2,4-oxadiazol-5-amine (4 a, TTNOA) exhibited a potential cast explosive component with low melting point at 88.2 °C and high onset decomposition temperature at 226.2 °C.