One‐pot Method for Reduction of Pyrazolo[5,1‐c][1,2,4]Triazine‐7‐diazonium Tetrafluoroborate to 7‐Hydrazinyl Derivatives

New convenient one‐pot method for reduction of hetarenediazonim tetrafluoroborates to the hetarylhydrazine derivatives was developed. Interaction of 8‐carboxyethyl‐3‐(tert‐butyl)‐4‐oxo‐4,6‐dihydropyrazolo[5,1‐c ][1,2,4]triazine‐7‐diazonium tetrafluoroborate with anhydrous SnCl₂ in anhydrous CF₃CO₂H, and further sequence of one‐pot operations led to formation of various derivatives of the unstable ethyl 3‐(tert‐butyl)‐7‐hydrazinyl‐4‐oxo‐4,6‐dihydropyrazolo[5,1‐c ][1,2,4]triazine‐8‐carboxylate (hydrochloride, hydrazides, hydrazones, and pyrazoles), which were isolated in high yields. The anhydrous conditions were first used with SnCl₂ and allowed to exclude hydrolysis of the ester group and formation of the by‐products.     

Regio‐ and Stereoselectivity in the Lewis Acid‐ and NaH‐Induced Reactions of Thiocamphor with (R)‐2‐Vinyloxirane

The reaction of the enolizable thioketone (1R,4R)‐thiocamphor (= (1R,4R)‐1,7,7‐trimethylbicyclo[2.2.1]heptane‐2‐thione; 1 ) with (R)‐2‐vinyloxirane ( 2 ) in the presence of a Lewis acid such as SnCl₄ or SiO₂ in anhydrous CH₂Cl₂ gave the spirocyclic 1,3‐oxathiolane 3 with the vinyl group at C(4′), as well as the isomeric enesulfanyl alcohol 4 . In the case of SnCl₄, an allylic alcohol 5 was obtained in low yield in addition to 3 and 4 (Scheme 2). Repetition of the reaction in the presence of ZnCl₂ yielded two diastereoisomeric 4‐vinyl‐1,3‐oxathiolanes 3 and 7 together with an alcohol 4 , and a ‘1 : 2 adduct’ 8 (Scheme 3). The reaction of 1 and 2 in the presence of NaH afforded regioselectively two enesulfanyl alcohols 4 and 9 , which, in CDCl₃, cyclized smoothly to give the corresponding spirocyclic 1,3‐oxathiolanes 3, 10 , and 11 , respectively (Scheme 4). In the presence of HCl, epimerization of 3 and 10 occurred to yield the corresponding epimers 7 and 11 , respectively (Scheme 5). The thio‐Claisen rearrangement of 4 in boiling mesitylene led to the allylic alcohol 12 , and the analogous [3,3]‐sigmatropic rearrangement of the intermediate xanthate 13 , which was formed by treatment of the allylic alcohol 9 with CS₂ and MeI under basic conditions, occurred already at room temperature to give the dithiocarbonate 14 (Schemes 6 and 7). The presented results show that the Lewis acid‐catalyzed as well as the NaH‐induced addition of (R)‐vinyloxirane ( 2 ) to the enolizable thiocamphor ( 1 ) proceeds stereoselectively via an S_N2‐type mechanism, but with different regioselectivity.     

Transition‐Metal‐Based Lewis Acid Catalysis of Aza‐Type Michael Additions of Amines to α,β‐Unsaturated Electrophiles in Water

Several transition‐metal‐based Lewis acid catalysts, especially FeCl₃?7 H₂O, CrCl₃?6 H₂O, and SnCl₄?4 H₂O, were shown to be highly effective for aza‐type Michael reactions between electrophilic α,β‐unsaturated compounds and both aliphatic and aromatic amines in aqueous solution. Advantages of the new protocol include 1) high‐yielding reactions that can be conducted at ambient temperature; 2) the use of inexpensive, stable transition‐metal salts as catalysts; and 3) plain H₂O as an environmentally benign solvent.     

Green Biginelli‐type Reaction: Solvent‐free Synthesis of 5‐unsubstituted 3,4‐dihydropyrimdin‐2(1H)‐ones

The Biginelli‐type compounds, 5‐unsubstituted 3,4‐dihydropyrimdin‐2(1H)‐ones were synthesized by a one‐pot three‐component condensation of aromatic aldehydes, aromatic ketones and urea in the presence of SnCl₄ · 5H₂O under solvent‐free conditions. The advantages of this method are short reaction time (4–10 min), excellent yields (74–97%), inexpensive catalyst and solvent‐free conditions. A plausible mechanism was proposed.     

Crystal Structures and Raman Spectra of cis‐[SnCl4(H2O)2]·2H2O,cis‐[SnCl4(H2O)2]·3H2O, [Sn2Cl6(OH)2(H2O)2]·4H2O,and [HL][SnCl5(H2O)]·2.5H2O (L=3‐acetyl‐5‐benzyl‐1‐phenyl‐4, 5‐dihydro‐1, 2, 4‐triazine‐6‐one oxime,C18H18N4O2)

The complexes cis‐[SnCl₄(H₂O)₂]·2H₂O ( 1 ), [Sn₂Cl₆(OH)₂(H₂O)₂]·4H₂O ( 3 ), and [HL][SnCl₅(H₂O)]·2.5H₂O ( 4 ) were isolated from a CH₂Cl₂ solution of equimolar amounts of SnCl₄ and the ligand L (L=3‐acetyl‐5‐benzyl‐1‐phenyl‐4, 5‐dihydro‐1, 2, 4‐triazine‐6‐one oxime, C₁₈H₁₈N₄O₂) in the presence of moisture. 1 crystallizes in the monoclinic space group Cc with a = 2402.5(1) pm, b = 672.80(4) pm, c = 1162.93(6) pm, β = 93.787(6)° and Z = 8. 4 was found to crystallize monoclinic in the space group P2₁, with lattice parameters a = 967.38(5) pm, b = 1101.03(6) pm, c = 1258.11(6) pm, β = 98.826(6)° and Z = 2. The cell data for the reinvestigated structures are: [SnCl₄(H₂O)₂]·3H₂O ( 2 ): a = 1227.0(2) pm, b = 994.8(1) pm, c = 864.0(1) pm, β = 103.86(1)°, with space group C2/c and Z = 4; 3 : a = 961.54(16) pm, b = 646.29(7) pm, c = 1248.25(20) pm, β = 92.75(1)°, space group P2₁/c and Z = 4.     

A series of substituted (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐ones

In the molecular structures of a series of substituted chalcones, namely (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one, C₂₁H₁₅FO₂, (I), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐fluorophenyl)prop‐2‐en‐1‐one, C₂₁H₁₄F₂O₂, (II), (2E)‐1‐(4‐chlorophenyl)‐3‐(2‐fluoro‐4‐phenoxyphenyl)prop‐2‐en‐1‐one, C₂₁H₁₄ClFO₂, (III), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₂, (IV), and (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methoxyphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₃, (V), the configuration of the keto group with respect to the olefinic double bond is s‐cis. The molecules pack utilizing weak C—H...O and C—H...π intermolecular contacts. Identical packing motifs involving C—H...O interactions, forming both chains and dimers, along with C—H...π dimers and π–π aromatic interactions are observed in the fluoro, chloro and methyl derivatives.     

Synthesis of 2,3‐diaryl‐3,4‐dihydro‐2H‐1,3‐benzoxazines and their fungicidal activities

A series of novel 2,3‐diaryl‐3,4‐dihydro‐2H‐1,3‐benzoxazines have been prepared in high yields from o‐arylaminomethylphenols and aromatic aldehydes in the presence of SnCl₄ for the first time, and their fungicidal activities were investigated too. Some of the products showed good fungicidal activities against Rhizoctonia solani justified by 100% activity of compound 1b. J. Heterocyclic Chem., (2010)     

Synthesis and reactions of 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]‐quinazolin‐9‐one and 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one

The reaction of 3‐N‐(2‐mercapto‐4‐oxo‐4H‐quinazolin‐3‐yl)acetamide ( 1 ) with hydrazine hydrate yielded 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 2 ). The reaction of 2 with o‐chlorobenzaldehyde and 2‐hydroxy‐naphthaldehyde gave the corresponding 3‐arylidene amino derivatives 3 and 4 , respectively. Condensation of 2 with 1‐nitroso‐2‐naphthol afforded the corresponding 3‐(2‐hydroxy‐naphthalen‐1‐yl‐diazenyl)‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 5 ), which on subsequent reduction by SnCl₂ and HCl gave the hydrazino derivative 6. Reaction of 2 with phenyl isothiocyanate in refluxing ethanol yielded thiourea derivative 7. Ring closure of 7 subsequently cyclized on refluxing with phencyl bromide, oxalyl dichloride and chloroacetic acid afforded the corresponding thiazolidine derivatives 8, 9 and 10 , respectively. Reaction of 2‐mercapto‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 11 ) with hydrazine hydrate afforded 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 12 ). The reactivity 12 towards carbon disulphide, acetyl acetone and ethyl acetoacetate gave 13, 14 and 15 , respectively. Condensation of 12 with isatin afforded 2‐[N‐(2‐oxo‐1,2‐dihydroindol‐3‐ylidene)hydrazino]‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 16 ). 2‐(4‐Oxo‐3‐phenylamino‐3,4‐dihydroquinazolin‐2‐ylamino)isoindole‐1,3‐dione ( 17 ) was synthesized by the reaction of 12 with phthalic anhydride. All isolated products were confirmed by their ir, ¹H nmr, ¹³C nmr and mass spectra.     

Synthese und Kristallstruktur des heterobimetallischen Diorganozinndichlorids (FcN,N)2SnCl2 (FcN,N—: (η5‐C5H5)Fe{(η5‐C5H3[CH(CH3)N(CH3)CH2CH2NMe2]‐2}—)

Synthesis and Crystal Structure of the Heterobimetallic Diorganotindichloride (FcN, N)₂SnCl₂ (FcN, N^—: (η⁵‐C₅H₅)Fe{η⁵‐C₅H₃[CH(CH₃)N(CH₃)CH₂CH₂NMe₂]‐2}^—) The heterobimetallic title compound [(FcN, N)₂SnCl₂] ( 1 ) was obtained by the reaction of [LiFcN, N] with SnCl₄ in the molar ratio 1:1 in diethylether as a solvent. The two FcN, N^— ligands in 1 are bound to Sn through a C‐Sn σ‐bond; the amino N atoms of the side‐chain in FcN, N^— remain uncoordinated. The crystals contain monomeric molecules with a pseudo‐tetrahedral coordination at the Sn atom: Space group P2₁/c; Z = 4, lattice dimensions at —90 °C: a = 9.6425(2), b = 21.7974(6), c = 18.4365(4) Å, β = 100.809(2)°, R1_obs· = 0.051, wR2_obs· = 0.136.     

Synthesis,Spectroscopic, and X‐Ray Diffraction Studies of cis‐Dichlorobis(4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl3 H‐pyrazol‐3‐onato) Tin(IV)

Reaction between an aqueous ethanol solution of tin(II) chloride and that of 4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐one in the presence of O₂ gave the compound cis‐dichlorobis(4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐onato) tin(IV) [(C₂₆H₂₆N₄O₄)SnCl₂]. The compound has a six‐coordinated Sn^IV centre in a distorted octahedral configuration with two chloro ligands in cis position. The tin atom is also at a pseudo two‐fold axis of inversion for both the ligand anions and the two cis‐chloro ligands. The orange compound crystallizes in the triclinic space group P 1 with unit cell dimensions, a = 8.741(3) Å, b = 12.325(7) Å, c = 13.922(7) Å; α = 71.59(4), β = 79.39(3), γ = 75.18(4); Z = 2 and D_x = 1.575 g cm^–3. The important bond distances in the chelate ring are Sn–O [2.041 to 2.103 Å], Sn–Cl [2.347 to 2.351 Å], C–O [1.261 to 1.289 Å] and C–C [1.401 Å] the bond angles are O–Sn–O 82.6 to 87.7° and Cl–Sn–Cl 97.59°. The UV, IR, ¹H NMR and ¹¹⁹Sn Mössbauer spectral data of the compound are reported and discussed.     

Syntheses and X‐Ray Crystal Structures of [Li(thf)4][SnCl5(thf)] and {[Li(Et2O)2]2‐(μ‐Cl2)2‐SnIVCl2}

The syntheses and single crystal X‐ray structure determinations are reported for [Li(thf)₄][SnCl₅(thf)] ( 1 ) and {[Li(Et₂O)₂]₂‐(μ‐Cl₂)₂‐Sn^IVCl₂} ( 2 ). Compound 1 is ionic with a tetrahedral coordinated lithium cation and distorted octahedral tin (IV) atom in the anion, while compound ( 2 ) is a centrosymmetric heteronuclear double salt of LiCl and SnCl₄. [Li(thf)₄][SnCl₅(thf)] is monoclinic, P2₁/n, a = 11.204(1), b = 15.599(1), c = 17.720(2) Å; β = 96.734(2)°, Z = 4, R 0.0418; {[Li(Et₂O)₂]₂‐(μ‐Cl₂)₂‐Sn^IVCl₂} is monoclinic, P2₁/n, a = 10.848(2), b = 12.764(2), c = 11.748(2) Å; β = 90.388(3)°, Z = 4, R = 0.0851.     

Synthesis of Isoindolo[2,1‐a]quinazoline‐5,11‐dione Derivatives via the Reductive One‐Pot Reaction of N‐Substituted 2‐Nitrobenzamides and 2‐Formylbenzoic Acids

Various isoindolo[2,1‐a]quinazoline‐5,11‐dione derivatives 3 were synthesized in good yields by means of the reductive reaction of N‐substituted 2‐nitrobenzamides 1 and 2‐formylbenzoic acids 2 in the presence of SnCl₂?2 H₂O under reflux in EtOH (Scheme, Table). The procedure needed two steps, the reduction of the nitro group of the 2‐nitrobenzamide and ring closure by nucleophilic addition of the NH₂ group to both the formyl and carboxylic acid C?O groups.     

A two‐dimensional cadmium(II) coordination polymer constructed from 4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylate and 1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylate ligands

Crystals of poly[[aqua[μ₃‐4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylato‐κ⁵O¹O^1′:N³,O⁴:O⁵][μ₄‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylato‐κ⁷N³,O⁴:O⁴,O^4′:O¹,O^1′:O¹]cadmium(II)] monohydrate], {[Cd₂(C₁₅H₁₄N₂O₄)(C₁₆H₁₄N₂O₆)(H₂O)]·H₂O}_n or {[Cd₂(Hcpimda)(cpima)(H₂O)]·H₂O}_n, (I), were obtained from 1‐(4‐carboxybenzyl)‐2‐propyl‐1H‐imidazole‐4,5‐dicarboxylic acid (H₃cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in‐situ decarboxylation of H₃cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd²⁺ centres, one 4‐carboxy‐1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐5‐carboxylate (Hcpimda²⁻) anion, one 1‐(4‐carboxylatobenzyl)‐2‐propyl‐1H‐imidazole‐4‐carboxylate (cpima²⁻) anion, one coordinated water molecule and one lattice water molecule. One Cd²⁺ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN₂O₄ geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda²⁻ ligand and three cpima²⁻ ligands. This Cd²⁺ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima²⁻ ligands bridge between Cd2 centres to generate [Cd₂O₂] units, which are further linked by two cpima²⁻ ligands to produce one‐dimensional (1D) infinite chains based around large 26‐membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda²⁻ ligands to generate 1D zigzag chains. The two types of chains are linked through a μ₂‐η² bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima²⁻ to give a two‐dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6‐coordinated net which has a (4³)₂(4⁶.6⁶.8³) topology. Furthermore, the FT–IR spectroscopic properties, photoluminescence properties, powder X‐ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.     

Stereochemical Course of the Reaction between Thiocarbonyl Compounds and Oxiranes: Reaction with cis‐ and trans‐2,3‐Dimethyloxirane

The reactions of thiocarbonyl compounds with cis‐2,3‐dimethyloxirane ( 1a ) in CH₂Cl₂ in the presence of BF₃⋅Et₂O or SnCl₄ led to trans‐4,5‐dimethyl‐1,3‐oxathiolanes, whereas with trans‐2,3‐dimethyloxirane ( 1b ) cis‐4,5‐dimethyl‐1,3‐oxathiolanes were formed. With the stronger Lewis acid SnCl₄, the formation of side‐products was also observed. In the case of 1,3‐thiazole‐5(4H)‐thione 2 , these side‐products are the corresponding 1,3‐thiazol‐5(4H)‐one 5 and the 1 : 2 adduct 8 (Schemes 2 – 4). Their formation can be rationalized by the decomposition of the initially formed spirocyclic 1,3‐oxathiolane and by a second addition onto the C=N bond of the 1 : 1 adduct, respectively. The secondary epimerization by inversion of the configuration of the spiro‐C‐atom (Schemes 5 – 7) can be explained by a Lewis‐acid‐catalyzed ring opening of the 1,3‐oxathiolane ring and subsequent ring closure to the thermodynamically more stable isomer (Scheme 12). In the case of 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone ( 20 ), apart from the expected spirocyclic 1,3‐oxathiolanes 21 and 23 , dispirocyclic 1 : 2 adducts were formed by a secondary addition onto the C=O group of the four‐membered ring (Schemes 9 and 10).     

Lanthanoidkomplexe von 1‐(2‐Propenyl)‐ und 1‐(3‐Butenyl)‐1,4,7,10‐tetraazacyclododecan‐4,7,10‐triessigsäure

η³‐1,4,7,10‐tetraazacyclododecane molybdenum tricarbonyl reacts with allyl bromide and 3‐butenyl bromide in dimethylformamide in the presence of K₂CO₃ yielding 1‐(2‐propenyl)‐1,4,7,10‐tetraazacyclododecane ( 1a ) and 1‐(3‐butenyl)‐1,4,7,10‐tetraazacyclododecane ( 1b ), which on their part react with bromoacetic acid tert‐butyl ester in CH₃CN to give 1‐(2‐propenyl)‐1,4,7,10‐tetraazacyclododecane‐4,7,10‐tris‐acetic acid tert‐butyl ester ( 2a ) and 1‐(3‐butenyl)‐1,4,7,10‐tetraazacyclododecane‐4,7,10‐tris‐acetic acid tert‐butyl ester ( 2b ), respectively. Compounds 2a and 2b are converted into the corresponding acids 1‐(2‐propenyl)‐1,4,7,10‐tetraazacyclododecane‐4,7,10‐tris‐acetic acid ( 4a ) (MPC) and 1‐(3‐butenyl)‐1,4,7,10‐tetraazacyclododecane‐4,7,10‐tris‐acetic acid ( 4b ) (MBC) via the trifluoroacetates 3a and 3b . Sm(NO₃)₃(H₂O)₆, LuCl₃(THF)₃, and TmCl₃(H₂O)₆ react with 4a and 4b forming the lanthanide complexes Sm(MPC) ( 5 ), Lu(MPC) ( 6 ), Tm(MPC) ( 7a ) and Tm(MBC) ( 7b ). The IR as well as the ¹H and ¹³C NMR spectra of the new compounds are reported and discussed.     

Reaction of Optically Active Oxiranes with Thiofenchone and 1‐Methylpyrrolidine‐2‐thione: Formation of 1,3‐Oxathiolanes and Thiiranes

The SnCl₄‐catalyzed reaction of (?)‐thiofenchone (=1,3,3‐trimethylbicyclo[2.2.1]heptane‐2‐thione; 10 ) with (R)‐2‐phenyloxirane ((R)‐ 11 ) in anhydrous CH₂Cl₂ at ?60° led to two spirocyclic, stereoisomeric 4‐phenyl‐1,3‐oxathiolanes 12 and 13 via a regioselective ring enlargement, in accordance with previously reported reactions of oxiranes with thioketones (Scheme 3). The structure and configuration of the major isomer 12 were determined by X‐ray crystallography. On the other hand, the reaction of 1‐methylpyrrolidine‐2‐thione ( 14a ) with (R)‐ 11 yielded stereoselectively (S)‐2‐phenylthiirane ((S)‐ 15 ) in 56% yield and 87–93% ee, together with 1‐methylpyrrolidin‐2‐one ( 14b ). This transformation occurs via an S_N2‐type attack of the S‐atom at C(2) of the aryl‐substituted oxirane and, therefore, with inversion of the configuration (Scheme 4). The analogous reaction of 14a with (R)‐2‐{[(triphenylmethyl)oxy]methyl}oxirane ((R)‐ 16b ) led to the corresponding (R)‐configured thiirane (R)‐ 17b (Scheme 5); its structure and configuration were also determined by X‐ray crystallography. A mechanism via initial ring opening by attack at C(3) of the alkyl‐substituted oxirane, with retention of the configuration, and subsequent decomposition of the formed 1,3‐oxathiolane with inversion of the configuration is proposed (Scheme 5).     

Synthesis of Bis‐Heterocyclic 1H‐Imidazole 3‐Oxides from 3‐Oxido‐1H‐imidazole‐4‐carbohydrazides

The reaction of 1H‐imidazole‐4‐carbohydrazides 1 , which are conveniently accessible by treatment of the corresponding esters with NH₂NH₂?H₂O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (=hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones 5 , the reaction in concentrated H₂SO₄ at room temperature gave 1,3,4‐thiadiazol‐2‐amines 6 . Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7 , which, under basic conditions, undergo cyclization to give 2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐ones 8 (Scheme 3). Treatment of 1 with Ac₂O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol‐2‐ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N‐oxide residue is retained. Furthermore, it was shown that imidazole N‐oxides bearing a 1,2,4‐triazole‐3‐thione or 1,3,4‐thiadiazol‐2‐amine moiety undergo the S‐transfer reaction to give bis‐heterocyclic 1H‐imidazole‐2‐thiones 11 by treatment with 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (Scheme 5).     

The diastereoisomers methyl 5‐(S)‐[2‐(R)/(S)‐methoxycarbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methylphenyl)‐4,5‐dihydropyrazole‐3‐carboxylate

The title diastereoisomers, methyl 5‐(S)‐[2‐(S)‐methoxy­carbonyl)‐2,3,4,5‐tetra­hydro­pyrrol‐1‐yl­carbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate and methyl 5‐(S)‐[2‐(R)‐methoxycarbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxylate, both C₁₉H₂₃N₃O₅, have been studied in two crystalline forms. The first form, methyl 5‐(S)‐[2‐(S)‐methoxy­carbonyl)‐2,3,4,5‐tetrahydropyrrol‐1‐ylcarbonyl]‐1‐(4‐methylphenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate–methyl 5‐(S)‐[2‐(R)‐methoxy­carbonyl)‐2,3,4,5‐tetra­hydro­pyrrol‐1‐yl­carbonyl]‐1‐(4‐methylphenyl)‐4,5‐dihydropyrazole‐3‐carboxylate (1/1), 2(S),5(S)‐C₁₉H₂₃N₃O₅·2(R),5(S)‐C₁₉H₂₃N₃O₅, contains both S,S and S,R isomers, while the second, methyl 5‐(S)‐[2‐(S)‐methoxycarbonyl)‐2,3,4,5‐tetrahydro­pyrrol‐1‐ylcarbonyl]‐1‐(4‐methyl­phenyl)‐4,5‐di­hydro­pyrazole‐3‐carboxyl­ate, 2(S),5(S)‐C₁₉H₂₃N₃O₅, is the pure S,S isomer. The S,S isomers in the two structures show very similar geometries, the maximum difference being about 15° on one torsion angle. The differences between the S,S and S,R isomers, apart from those due to the inversion of one chiral centre, are more remarkable, and are partially due to a possible rotational disorder of the 2‐­(methoxycarbonyl)tetrahydropyrrole group.     

An efficient and regiospecific preparation of trifluoromethyl substituted 4‐( 1H‐pyrazol‐1 ‐yl)‐7‐chloroquinolines

A new series of 4‐[3‐alkyl(aryl)(heteroaryl)‐5‐hydroxy‐5‐trifluoromethyl‐4,5‐dihydro‐1H‐pyrazol‐1‐yl]‐7‐chloroquinolines, where [alkyl = CH₃; aryl = C₆H₅, 4‐CH₃C₆H₄, 4‐FC₆H₄, 4‐ClC₆H₄, 4‐BrC₆H₄, 4‐CH₃OCgH₄, 4‐NO₂CgH₄, 4‐biphenyl, 1‐naphthyl; heteroaryl = 2‐furyl and 2‐thienyl] has been regiospecifi‐caly obtained from the reaction of 7‐chloro‐4‐hydrazinoquinoline with 4‐substituted‐l,1,1‐trifluoro‐4‐methoxybut‐3‐en‐2‐ones in 61 ‐ 96 % yield. Subsequently, dehydration reaction of 4,5‐dihydropyra‐zolylquinolines under acid conditions furnished a new series of 4‐(3‐substituted‐5‐trifluoromethyl‐1H‐pyra‐zol‐1‐yl)‐7‐chloroquinolines in 73 ‐ 96 % yield.     

Enantioselective Access to (−)‐Ambrox® Starting from β‐Farnesene

Starting from inexpensive (E)‐β‐farnesene ( 1 ), an eight‐step enantioselective synthesis of the olfactively precious Ambrox^® ((?)‐ 2a ) has been performed. The crucial step is the catalytic asymmetric isomerization of (2E,6E)‐N,N‐diethylfarnesylamine ( 3 ) to the corresponding enamine (?)‐(R,E)‐ 4a , applying Takasago's well‐known industrial methodology. The resulting dihydrofarnesal ((+)‐(R)‐ 5 ) (90% yield, 96% ee), obtained after in situ hydrolysis (AcOH, H₂O), was then cyclized under catalytic SnCl₄ conditions, via its corresponding unreported enol acetate (?)‐(R)‐ 4b , to afford trans‐decalenic aldehyde (+)‐ 6a . Subsequent transformations furnished bicyclic ketone (?)‐ 8a and unsaturated nitrile (+)‐ 11 , both reported as intermediates to access to (?)‐ 2a .