Influence ofE/Z isomerism of aldoximes on the direction of their alkylation with oxirane

The reaction ofZ-2-furaldoxime with oxirane afforded theN-alkylation product,viz., α-2-furyl-N-(2-hydroxyethyl)nitron, in good yield.E-Benzaldoxime gave predominantly theO-alkylation product, while itsZ isomer was converted into a mixture with theN-alkylation product slightly predominating.     

Alkylation of 4,5-dichloropyridazin-6-one with α,ω-dibromoalkanes or 4,5-dichloro-1-(ω-bromoalkyl)pyridazin-6-ones

Alkylations of 4,5-dichloropyridazin-6-one (1) with dibromoalkanes 2 or 3 in the presence of potassium carbonate or tetrabutylammonium bromide/potassium hydroxide were investigated under restricted condition. Reactions of 1 with 2 or 3, except for 2b and 3b , in the presence of potassium carbonate or tetrabutylammonium bromide/potassium hydroxide gave only the N-alkylation products 3 and/or 4. Alkylation of 1 with 2b or 3b in the presence of potassium carbonate yielded the N-alkylation products 3b and/or 4b and the O-alkylation product 5 as the main product, whereas treatment of 1 with 2b or 3b in the presence of tetrabutylammonium bromide/potassium hydroxide afforded selectively the N-alkylation products 3b and/or 4b.     

The reactions of arylamines with chelidonic acid

Depending on the conditions, and the basicity of the amine, arylamines react with chelidonic acid to yield five different types of product: salts, N-arylchelidamic acids, N-aryl-4-pyridone-2-carboxylic acids, N-aryl-4-pyridones, or chelidamic acid itself.     

Effect of the Nature of the Substituent in N‐Alkylimidazole Ligands on the Outcome of Deprotonation: Ring Opening versus the Formation of N‐Heterocyclic Carbene Complexes

Complexes [Re(CO)₃(N‐RIm)₃]OTf (N‐RIm=N‐alkylimidazole, OTf=trifluoromethanesulfonate; 1 a – d ) have been straightforwardly synthesised from [Re(OTf)(CO)₅] and the appropriate N‐alkylimidazole. The reaction of compounds 1 a – d with the strong base KN(SiMe₃)₂ led to deprotonation of a central C? H group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1 a contains three N‐MeIm ligands, and its product 2 a features a C‐bound imidazol‐2‐yl ligand. When 2 a is treated with HOTf or MeOTf, rhenium N‐heterocyclic carbenes (NHCs) 3 a or 4 a are afforded as a result of the protonation or methylation, respectively, of the non‐coordinated N atom. The reaction of 2 a with [AuCl(PPh₃)] led to the heterobimetallic compound 5 , in which the N‐heterocyclic ligand is once again N‐bound to the Re atom and C‐coordinated to the gold fragment. For compounds 1 b – d , with at least one N‐arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2? H group of an imidazole ligand attacks a central C? H group of a neighbouring N‐RIm ligand, thus affording the product of C? C coupling and ring‐opening of the imidazole moiety that has been attacked ( 2 c , d ). The new complexes featured an amido‐type N atom that can be protonated or methylated, thus obtaining compounds 3 c , d or 4 c , d , respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring‐opening of the N‐RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring‐opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N‐heterocyclic ligand to afford the imidazol‐2‐yl product.     

One-step synthesis of N-[(methylthio)methyl]imidazole and related heterocyclic derivatives via a fummerer rearrangement

N-[(Methylthio)methyl]imidazole may be prepared from dimethylsulfoxide and N-(trimethylsilyl)imidazole or N-(t-butyldimethylsilyl)imidazole at elevated temperatures via a Purnmerer rearrangement. The product was characterized by elemental analysis, mass spectrometry and proton and carbon nmr. Preliminary experiments show that corresponding derivatives of 2-methylimidazole, pyrazole, triazole and benzimidazole may also be prepared in an analogous manner.     

Diastereoselective Addition of Allyl Reagents to Variously N‐Monoprotected and N,N‐Diprotected L‐Alaninals

Diastereoselective C₃‐elongation processes of N‐Boc‐, N‐Z‐, N‐Bn‐N‐Boc‐, and N‐Bn‐N‐Z‐L ‐alaninals (Boc=^tBuOCO, Z=PhCH₂OCO, Bn=PhCH₂) using various allyl reagents, such as allyl bromide in the presence of Zn/aqueous NH₄Cl solution, of SnCl₂⋅2 H₂O/NaI or of Mg/CuCl₂⋅2 H₂O, as well as allyltrichlorosilane, are described. A substantially different influence of the N‐protecting groups replacing either one or two amino protons was observed, allowing the selective synthesis of either the syn‐ or anti‐diastereoisomer as a major product.     

Products of class operators of the symmetric group

A combinatorial derivation of the product of the class of three cycles, [(1)^N?3(3)]_N with an arbitrary class operator of the symmetric group S_N is presented. The form of this result suggests a conjecture concerning the expression of the general class operator product in terms of a relatively small number of reduced class coefficients. The conjecture is applied to the determination of the products of [(1)^N?4(4)]_N, [(1)^N?4(2)²]_N, and [(1)^N?5(5)]_N with arbitrary class operators. General expressions for the reduced class coefficients of the simplest type are obtained.     

Reaction of γ-dicarboxylic acids amides and imides with trifluoromethanesulfonamide and formaldehyde

Three-component condensation of trifluoromethanesulfonamide with paraformaldehyde and succinamide depending on the reaction conditions led alongside bis(trifluoromethanesulfonamido)methane to the formation of a substitution product, bis[(trifluoromethylsulfonyl)aminomethyl]succinamide, or to a cyclization product, N-[trifluoromethylsulfonyl)aminomethyl]succinimide. The attempt to obtain the latter by the reaction of the trifluoromethanesulfonamide sodium salt CF₃SO₂NHNa with N-chloromethylsuccinimide unexpectedly resulted in N,N-bis(succinimidomethyl)-trifluoromethanesulfonamide. Analogously the reaction of CF₃SO₂NHNa with N-chloromethyl-phthalimide gave N,N-bis(phthalimidomethyl)trifluoromethanesulfonamide. The reaction of CF₃SO₂NHNa with succinimide and phthalimide in water and alcohol solution resulted in the ring opening and further transformation of the formed monosubstituted N-(trifluoromethylsulfonyl)amides of succinic and phthalic acids.     

Diastereo‐ and Regioselective Addition of Thioamide Dianions to Imines and Aziridines: Synthesis of N‐Thioacyl‐1,2‐diamines and N‐Thioacyl‐1,3‐diamines

Addition reactions of thioamide dianions that were derived from N‐arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N‐thioacyl‐1,2‐diamines in a highly diastereoselective manner in good‐to‐excellent yields. The diastereomeric purity of these N‐thioacyl‐1,2‐diamines could be enriched by simple recrystallization. The reduction of N‐thioacyl‐1,2‐diamines with LiAlH₄ gave their corresponding 1,2‐diamines in moderate‐to‐good yields with retention of their stereochemistry. The oxidative‐desulfurization/cyclization of an N‐thioacyl‐1,2‐diamine in CuCl₂/O₂ and I₂/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N‐tosylaziridines gave the addition products of N‐thioacyl‐1,3‐diamines with low diastereoselectivity but high regioselectivity and in good‐to‐excellent yields. The use of AlMe₃ as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X‐ray diffraction.     

The non-N-representability of the Colle–Salvetti second-order reduced density matrix

The Colle–Salvetti second-order reduced density matrix (2-matrix) is an approximation to the 2-matrix obtained from a wave function that is a product of a reference wave function containing little or no correlation times a product of correlation factors that are functions of the coordinates of pairs of electrons. A formal proof is given for the non-N-representability for the Colle–Salvetti 2-matrix using the nonnegativity condition of the 2-matrix. The nonnegativity condition of the particle-hole overlap matrix (G matrix) is also not satisfied. The proof is valid for Colle–Salvetti 2-matrices obtained from both the Hartree–Fock and small multiconfigurational-self-consistent-field wave functions. Even though the Colle–Salvetti 2-matrix is not N-representable, it does satisfy the Pauli principle component of the G-matrix condition because it reduces to an N-representable first-order reduced density matrix. © 1993 John Wiley & Sons, Inc.     

Reactions of some arenes and pyrazoles in MeCN under conditions of undivided-cell electrolysis

As exemplified for the first time by pyrazole and its 4-nitro and 3,5-dimethyl derivatives, N-arylation of pyrazoles can be performed under conditions of undivided-cell amperostatic electrolysis (Pt electrodes, MeCN) of systems containing the pyrazolate anion and (or) pyrazole, arene (benzene, 1,4-dimethoxybenzene, or xylene), and a supporting electrolyte. In the case of electrolysis involving 1,4-dimethoxybenzene as arene, N-arylation followed simultaneously three routes to form an ortho-substitution product (1,4-dimethoxy-2-(pyrazol-1-yl)benzene), an ipso-substitution product (4-methoxy-1-(pyrazol-1-yl)benzene), and an ipso-bisaddition product (1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-diene) in a total current yield of up to 50%. The acid-base properties of the pyrazoles under study affect the ratio of the N-arylation products and govern the required composition of the starting reaction mixture. In the case of a stronger base, such as 3,5-dimethylpyrazole, N-arylation with 1,4-dimethoxybenzene occurred even in the pyrazole—arene—tetraalkylammonium perchlorate system, whereas N-arylation of 4-nitropyrazole (a weaker base) proceeded only in the presence of the pyrazolate anion or another base, viz., sym-collidine. Oxidation of arene to the radical cation is the key anodic reaction. Not only the pyrazolate anion, but also highly basic pyrazole or a solvate complex of weakly basic pyrazole with collidine can serve as a nucleophilic partner in subsequent transformations of these radical cations.     

arachno-Diazapentaboranes

The reaction of appropriate amounts of BH₃ with diazadiboretidines (RBNtBu)₂ ( 1a–e ; R = Et, Pr, Bu, tBu, tBu(Me₃Si)N) transforms them into cyclic diazapentaboranes either of the type [ RB (H₂) BR NtBu BH NtBu ] ( 2a–c ), of the type [ HB (H₂) BR NtBu BH NtBu ] ( 3a–d ), or of the type [ HB (H₂) BH NtBu BH NtBu ] ( 4 ), or into an acyclic product RBH NtBu BH NtBu BHR ( 2e ). The structure of 3c is characterized by a planar N₂B₃ ring skeleton with an unsymmetrical double-hydrogen bridge.     

Reaction of dichloroketene and sulfene with N,N-disubstituted 6-amino-methylene-b,7,8,9 -tetrahydro-5H-benzocyclohepten-5-ones. Synthesis of 6-(2,2-Dichloroethylidene)-b,7,8,9-tetrahydro-5H-benzocyclohepten-5-one and of 5H-benzo[3,4]cyclohepta[2,l-b]pyran and 5H-Benzo[3,4]cyclo-hepta[1,2-e]-1,2-oxathiin derivatives

The 1,4-cycloaddition of dichloroketene to N,N-disubstituted 6-aminomethylene-b,7,8,9-tetra-hydro-5H-benzocyclohepten-5-ones afforded N,N-disubstituted 4-amino-3,3-dichloro-3,4,6,7-tetrahydro-5H-benzo[3,4]cyclohepta[2,l-b]pyran-2-ones only in the case of aromatic or strong hindering aliphatic N-substitution. The adducts gave N,N-disubstituted 4-amino-3-chloro-b,7-dihydro-5H-benzo[3,4]cyclohepta[2,l-b]pyran-2-ones by dehydrochlorination with collidine. Upon chromatography on neutral alumina, two products were instead isolated in the case of usual aliphatic N-substitution (diethylamine, piperidine), namely 6-(2,2-dichloroethylidene)-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-one and the dehydrochlorinated 2-pyrone; this latter was the sole product in the case of pyrrolidine substitution. The 1,4-cycloaddition of sulfene occurred readily to give N,N-disubstituted 4-amino-3,4,6,7-tetrahydro-5H-benzo[3,4]cyclohepta-[1,2-e]-1,2-oxathiin 2,2-dioxidesin the case of both aliphatic and partially aromatic N-substitution.     

Study on the structures of 2-substituted iminothiazolidine derivatives

The reaction of 2-bromoethylamine 1 with methylisothiocyanate 2 under mild condition gave 2-methyl-amino-2-thiazoline 3 as the major product together with two kinds of byproducts, 3-(N-methylthiocar-bamoyl)-2-methyliminothiazolidine 4 and N,N′-dimethyl-N-(2-thiazolin-2-yl)thiourea 5. Thermal isomer-ization of 5 to 4 was observed. The structures of the byproducts were confirmed by X-ray crystallography.     

Formation and reactions of substituted diazocyclopropanes and cyclopropyldiazonium ions

Decomposition of N-nitroso-N-cyclopropylureas at 5—7 °C on treatment with K₂CO₃ containing 15—20% H₂O allows simultaneous generation of both substituted diazocyclopropanes and cyclopropyldiazonium ions, which can react according to 1,3-dipolar cycloaddition or azo-coupling pattern with appropriate substrates. The nature of substituents in the cyclopropyl ring have a pronounced influence on the product ratio (and, probably, on the equilibrium between the diazo compound and the diazonium ion). Thus, on treatment with a base in the presence of equimolar amounts of methyl metacrylate as a trap for the diazo compound and 2-naphthol as a trap for the diazonium ion, N-cyclopropyl- and N-(2,2-dimethylcyclopropyl)-N-nitrosourea azo coupling products predominate. Conversely, N-(2,2-dichlorocyclopropyl)-N-nitrosourea is transformed predominantly into 1,3-cycloaddition products. A rationalization for the experimental data is proposed.     

Synthesis of 6-cyanopurines and the isolation and X-ray structure of novel 2H-pyrroles

(Z)-N¹-(2-Amino-1,2-dicyanovinyl)-N²-substituted-formainidines react with dimethylformamide diethyl acetal at room temperature to give 6-cyanopurines as the major product together with novel 5-amino-2-arylimino-3,4-di[(N,N-dimethylamino)methylideneamino]-2H-pyrroles, which have been fully characterised and a single crystal X-ray analysis has been carried out on the N-phenyl derivative.     

Regio- and Stereoselective Synthesis of γ-Alkylidenebutenolides by Cyclization of Dilithiated 1,3-Dicarbonyl Compounds with N,N′-Dimethoxy-N,N′-dimethylethane- diamide

The remarkably simple synthesis of γ-alkylidenebutenolides 3 is achieved by cyclization of the dilithiated 1,3-dicarbonyl compounds 1 with N,N′-dimethoxy-N,N′-dimethylethanediamide ( 2 ). This regio- and stereoselective cyclization provides a route to a wide range of butenolides, which are of pharmacological relevance and of importance for natural product synthesis.     

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines. Structural Effects on Rates and Products

A kinetic and product study of the reaction of a series of α‐methyl‐substituted N‐methylpiperidines with thermally generated ¹O₂ in MeCN was carried out. It was found that as the number of α‐methyl groups (Me in α‐position relative to the N‐atom) increases, the rate of ¹O₂ quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N‐demethylation products and N‐formyl derivatives. The same trend was observed for the ratio between N‐demethylation and formation of the N‐formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme 1 where an exciplex is first formed that by a H‐atom transfer process produces an α‐amino‐substituted C‐radical. The latter forms the product of N‐demethylation by one electron oxidation, or affords the N‐formyl derivative by radical coupling (Scheme 1). Similar results were obtained with N,N‐dimethylcyclohexanamine. However, this ‘acyclic’ amine exhibited behaviors quite distinct from those of the N‐methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio.     

The thermolysis of heterocyclic aminimines

Aminimines derived from six heterocyclic tertiary amines were thermolyzed in t-butyl alcohol at ca. 80°. N-Methylindoline gave a good yield of the ring-opened product, and a double elimination on 1,4,4-trimethyl-piperidine gave 3,3-dimethyl-1,4-pentadiene. The aminimine derived from quinuclidine was stable to elimination under these conditions. Simple elimination products were not obtained from N-methyl-pyrrolidine, N-methylpiperidine, or N-methyltetrahydroisoquinoline.     

Synthesis,Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

We report a detailed study of the reactions of the Ti?NNCPh₂ alkylidene hydrazide functional group in [Cp*Ti{MeC(NiPr)₂}(NNCPh₂)] ( 8 ) with a variety of unsaturated and saturated substrates. Compound 8 was prepared from [Cp*Ti{MeC(NiPr)₂}(NtBu)] and Ph₂CNNH₂. DFT calculations were used to determine the nature of the bonding for the Ti?NNCPh₂ moiety in 8 and in the previously reported [Cp₂Ti(NNCPh₂)(PMe₃)]. Reaction of 8 with CO₂ gave dimeric [(Cp*Ti{MeC(NiPr)₂}{μ‐OC(NNCPh₂)O})₂] and the “double‐insertion” dicarboxylate species [Cp*Ti‐{MeC(NiPr)₂}{OC(O)N(NCPh₂)C(O)O}] through an initial [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(O)O}], the congener of which could be isolated in the corresponding reaction with CS₂. The reaction with isocyanates or isothiocyanates tBuNCO or ArNCE (Ar=Tol or 2,6‐C₆H₃iPr₂; E=O, S) gave either complete NNCPh₂ transfer, [2+2] cycloaddition to Ti?N_α or single‐ or double‐substrate insertion into the Ti?N_α bond. The treatment of 8 with isonitriles RNC (R=tBu or Xyl) formed σ‐adducts [Cp*Ti{MeC(NiPr)₂}(NNCPh₂)(CNR)]. With Ar^F5CCH (Ar^F5=C₆F₅) the [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(Ar^F5)C(H)}] was formed, whereas with benzonitriles ArCN (Ar=Ph or Ar^F5) two equivalents of substrate were coupled in a head‐to‐tail manner across the Ti?N_α bond to form [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(Ar)NC(Ar)N}]. Treatment of 8 with RSiH₃ (R=aryl or Bu) or Ph₂SiH₂ gave [Cp*Ti{MeC(NiPr)₂}{N(SiHRR′)N(CHPh₂)}] (R′=H or Ph) through net 1,3‐addition of Si? H to the N? N?CPh₂ linkage of 8 , whereas reaction with PhSiH₂X (X=Cl, Br) led to the Ti?N_α 1,2‐addition products [Cp*Ti{MeC(NiPr)₂}(X){N(NCPh₂)SiH₂Ph}].