Novel diazadienes based on 1,3,4-oxadiazines: Ligands in iron carbonyl complexes and substrates in catalytic [2+2+1] cycloaddition reactions

N,N′-(4-methyl-4H-1,3,4-oxadiazine-5,6-diylidene)-bis-aniline derivatives react with Fe₂(CO)₉ to give dinuclear iron carbonyl complexes. One of the iron atoms is bonded symmetrically to both exocyclic imine nitrogen atoms. The second iron atom shows a side-on coordination towards the CN bond next to the oxadiazine oxygen atom. In addition, the iron atoms are connected via a metal metal bond. The same oxadiazine derivatives produce chiral spiro-lactams in a ruthenium catalyzed formal [2+2+1] cycloaddition reaction with carbon monoxide and ethylene.     

Synthesis of Spiro‐Heterocycles with the Thiazolidinone Moiety from Nitrilimines

The 2‐phenylimino‐1,3‐thiazolidin‐4‐one 2 was obtained by thermal cyclization of 4‐amino‐5‐phen‐yl‐3, 5‐thiaaza‐4‐pentenoic acid 1 using DCC as dehydration agent. Treatment of 2‐phenylimino‐1,3‐thiazolidin‐4‐one 2 with various hydrazonoyl halides 3 (nitrilimines 4 precursor) yielded 6‐aryl‐9‐phenyl‐8‐substituted‐1,4,6,7,9‐thiatetrazaspiro‐[4.4]non‐7‐en‐3‐ones 5a‐1. Both analytical and spectroscopic data of all the synthesized compounds are in full agreement with the proposed structures.     

The potential energy surface of the triazadiphosphole formation

The formal GaCl₃-assisted [3+2] cycloaddition of two (Me₃Si)₂N–N(SiMe₃)–PCl₂ molecules resulting in the formation of a triazadiphosphole has been studied by means of B3LYP/6-31G(d,p) computations. These calculations revealed a stepwise reaction mechanism starting from the disguised 1,3-dipole and dipolarophile (Me₃Si)₂N–N(SiMe₃)–PCl₂. Comparison of the potential energy surface for the formation of a triazadiphosphole in the presence and without a Lewis acid indicate, that addition of a Lewis acid such as GaCl₃ decreases the activation barriers to Me₃Si–Cl elimination, in accord with experiment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Formation of pyridine from acetylenes and nitriles catalyzed by RuCpCl, CoCp, and RhCp derivatives - A computational mechanistic study

The mechanism of the catalytic formation of pyridines from the coupling of two alkynes and the nitriles NCR (R = H, Me, Cl, COOMe) with the fragments CpRuCl, CpCo, and CpRh has been investigated by means of DFT/B3LYP calculations. According to the proposed mechanism, the key reaction step is the oxidative coupling of two alkyne ligands to give metallacyclopentatriene (Ru, Rh) and metallacyclopentadiene (Co) intermediates. In the case of ruthenium, this process is thermodynamically clearly favored over the oxidative coupling between one alkyne and one nitrile ligand to afford an azametallacycle. This alternative pathway however cannot be dismissed in the case of Co and Rh. The rate determining step of the overall catalytic cycle is the addition of a nitrile molecule to the metallacyclopentatriene and metallacyclopentadiene intermediates, respectively, which has to take place in a side-on fashion. Competitive alkyne addition leads to benzene formation. Thus, also the chemoselectivity of this reaction is determined at this stage of the catalytic cycle. In the case of the RuCpCl fragment, the addition of nitriles R-CN and acetylenes RCCH has been studied in more detail. For R = H, Cl, and COOMe the side-on addition of nitriles is kinetically more favored than alkyne addition and, in accordance with experimental results, pyridine formation takes place. In the case of R = Me nitrile addition could not be achieved and the addition of alkynes to give benzene derivatives seems to be kinetically more favored. Once the nitrile is coordinated facile C-C bond coupling takes place to afford an unusual five- and four-membered bicyclic ring system. This intermediate eventually rearranges to a very unsymmetrical azametallaheptatriene complex which in turn provides CpRuCl(κ¹-pyridine) via a reductive elimination step. Completion of the catalytic cycle is achieved by an exergonic displacement of the respective pyridine product by two acetylene molecules regenerating the bisacetylene complex.     

Synthesis and chemistry of aryloxygermylene-amine complexes

The synthesis of stable monomeric dimesityloxygermylene-amine (MesO)₂Ge-NR₃ [NR₃ = Et₂NH, (C₆H₁₁)₂NH, Et₃N, dabco, tmeda] and chloromesityloxygermylene-amine MesO(Cl)Ge-tmeda complexes is presented. All compounds have been fully characterized by spectroscopic methods. The insertion reaction of (MesO)₂Ge-tmeda 1a with dimethyl disulfide, bis(trimethylsilyl)peroxide and iodomethane is reported. Cycloaddition reactions with dimethylbutadiene are especially effective without any activation and with dimethyl acetylenedicarboxylate led selectively to compounds 7 and 8. In the latter case, the transient formation of a germirene has been evidenced by a trapping reaction. The structures of 3, 7 and 8 were determined by single-crystal X-ray diffraction.     

Reactivity of [CpRh(η-C6H3NH2-2,6-i-Pr2)](OTf)2 toward phosphines and alkynes

The cationic aniline complex [Cp^∗Rh(η⁶-2,6-(Me₂CH)₂C₆H₃NH₂)](OTf)₂ (1) was prepared from either [Cp^∗Rh(η²-NO₃)(η¹-OTf)] or [Cp^∗Rh(OH₂)₃](OTf)₂ and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile character of the η⁶-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimerization for PhCCPh and the [2 + 2 + 1] trimerization for PhCCH and CH₃C₆H₄CCH. The unexpected cyclobutadiene complex [Cp^∗Rh(η⁴-C₄(C(O)CH₃)₂H(SiMe₃))] was obtained from complex 1 and Me₃SiCCCCSiMe₃ and structurally characterized by X-ray diffraction.     

[3+2]- Versus [4+2]-cycloaddition reactions of 3-methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles with N-substituted maleimides involving pyrrolidine-derived azomethine ylides

3-Methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles do not enter into [4+2]-cycloaddition reactions with maleimides to form the expected pyrrolo-pyridazines. Instead the formation of novel pyrrolo-pyridazines of type 4 takes place via a formal [3+2]-cycloaddition of initially formed pyrrolidine-derived azomethine ylides 7. The mechanism leading to the final product is discussed.     

Fluoropropenoates as dienophiles in the Diels-Alder reaction

Several fluorinated alkenes were prepared from known ethyl (R)-2-fluoro-4,5-dihydroxyisopropylidine-2-pentenoate (1). The fluoroalkenoates were tested as dienophiles with several dienes and showed cycloaddition only with the very reactive diene, 1,3-diphenylisobenzofuran (5). Fluorobutenolide 2 reacted with 5 to produce the endo-syn adduct 9 in a highly stereoselective manner.     

一种合成3,5-二取代异噁唑的新方法

研究了端基炔烃和醛肟在间氯过氧苯甲酸和催化量碘苯作用下的[3+2]环合反应, 结果表明, 该过程经过一个有机高价碘中间体而进行. 通过该反应, 端基炔烃在氧化剂间氯过氧苯甲酸和催化剂碘苯的作用下与醛肟反应, 常温下可得到产率良好并具有区域选择性的3,5-二取代异噁唑化合物. 本文考察了反应条件的影响, 提出了可能的反应机理, 为简便快速合成3,5-二取代异噁唑化合物提供了一种新方法.     

Synthesis of new 1,2,4-oxadiazolidin-5-ylthiophenes and thienopyrimidine derivatives by aza-Wittig reaction using a thienyl carbodiimide

Azidation of aminothiophene derivative 1 afforded the corresponding azido derivative 2.The latter reacted with triphenylphosphine to afford iminophosphorane derivatives 3.Reacting 3 with phenylisocyanate gave the highly reactive carbodiimide intermediate 4,which was reacted with different nitrones to afford new l,2,4-oxadiazolidin-5-ylidene-aminothiophenes 5a-c. Treatment of 4 with absolute EtOH at room temperature gave methyleneamino-5-(methylthio)thiophene 7,(methylthio)-3-(3- phenylureidothiophene)-2-carboxylate 8 or thienopyrimidine 9 and 10 at refluxing temperature.Finally reaction of carbodiimide intermediate 4 with different secondary amines gave the new thienopyrimidines 11a-c.