Acid-Mediated Electrocyclic Domino Transformations of 5,5-Disubstituted 1-Amino-1-azapenta-1,4-dien-3-ones into Dihydrospiroindenepyrazole and Dihydroindenodiazepine Derivatives

Trifluoromethyl-substituted 1-amino-1-azapenta-1,4-dien-3-ones 4, which are accessible in good yield from pyruvates 1 in a three-step procedure, undergo a cascade reaction involving inter alia two electrocyclizations upon treatment with a large excess of trifluoromethanesulfonic acid to give novel dihydrospiroindenepyrazole 5a−o and dihydroindenodiazepine 6a−j. We interpret this sequence of reactions on the basis of quantum chemical calculations as a dicationic cyclization of a pentadien-1-one (“superelectrophilic solvation”), where one of the double bonds is part of an aromatic ring and a subsequent rearrangement to form an (monocationic) iminium ion, which either cyclizes to give five-membered spiro ring systems (compounds 5) or tricyclic dihydroindenodiazepine derivatives 6. Hückel- and Möbius-type transition states of the electrocyclization reactions are discussed considering the results of NICS calculations. One 1-amino-1-penta-1,4-dien-3-one 4 and several dihydrospiroindenepyrazoles 5 and dihydroindenodiazepines 6 could be characterized by X-ray diffraction

Acid-Mediated Electrocyclic Domino Transformations of 5,5-Disubstituted 1-Amino-1-azapenta-1,4-dien-3-ones into Dihydrospiroindenepyrazole and Dihydroindenodiazepine Derivatives

Trifluoromethyl-substituted 1-amino-1-azapenta-1,4-dien-3-ones 4, which are accessible in good yield from pyruvates 1 in a three-step procedure, undergo a cascade reaction involving inter alia two electrocyclizations upon treatment with a large excess of trifluoromethanesulfonic acid to give novel dihydrospiroindenepyrazole 5a−o and dihydroindenodiazepine 6a−j. We interpret this sequence of reactions on the basis of quantum chemical calculations as a dicationic cyclization of a pentadien-1-one (“superelectrophilic solvation”), where one of the double bonds is part of an aromatic ring and a subsequent rearrangement to form an (monocationic) iminium ion, which either cyclizes to give five-membered spiro ring systems (compounds 5) or tricyclic dihydroindenodiazepine derivatives 6. Hückel- and Möbius-type transition states of the electrocyclization reactions are discussed considering the results of NICS calculations. One 1-amino-1-penta-1,4-dien-3-one 4 and several dihydrospiroindenepyrazoles 5 and dihydroindenodiazepines 6 could be characterized by X-ray diffraction

Synthesis of Catechols from Phenols via Pd-Catalyzed Silanol-Directed C–H Oxygenation

A silanol-directed, Pd-catalyzed C–H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product

3-(Hetero)aryl-4-indolylamino-α-tetralones by Diastereoselective Internal Redox Cyclization: An “Azaenamine” Conjugate Addition

(E)-3-(Hetero)aryl-1-(2-((E)-(indolin-1-ylimino)methyl)phenyl)prop-2-en-1-ones 1 undergo 6-exo-trig cyclization reactions upon treatment with BF3·Me2S in dichloromethane at low temperature to give the tetralones 10 in good yield. This cyclization process can be considered to be an intramolecular Michael-type addition which is accompanied by an internal redox reaction as the indoline fragment is oxidized to indole with simultaneous hydrogen shift to nitrogen atom N1 and the α-carbon atom of the Michael system. The reactions at the iminic centers take place via umpolung of the classical carbonyl reactivity. The reaction is diastereoselective and affords exclusivly 3,4-disubstituted α-tetralones 10 as trans-diastereomers. According to quantum chemical calculations the reactions take place under kinetic control with the trans-diastereomer being the kinetically favored product as it has the lower activation barrier compared to the cis-diastereomer

3-(Hetero)aryl-4-indolylamino-α-tetralones by Diastereoselective Internal Redox Cyclization: An “Azaenamine” Conjugate Addition

(E)-3-(Hetero)aryl-1-(2-((E)-(indolin-1-ylimino)methyl)phenyl)prop-2-en-1-ones 1 undergo 6-exo-trig cyclization reactions upon treatment with BF3·Me2S in dichloromethane at low temperature to give the tetralones 10 in good yield. This cyclization process can be considered to be an intramolecular Michael-type addition which is accompanied by an internal redox reaction as the indoline fragment is oxidized to indole with simultaneous hydrogen shift to nitrogen atom N1 and the α-carbon atom of the Michael system. The reactions at the iminic centers take place via umpolung of the classical carbonyl reactivity. The reaction is diastereoselective and affords exclusivly 3,4-disubstituted α-tetralones 10 as trans-diastereomers. According to quantum chemical calculations the reactions take place under kinetic control with the trans-diastereomer being the kinetically favored product as it has the lower activation barrier compared to the cis-diastereomer

3-(Hetero)aryl-4-indolylamino-α-tetralones by Diastereoselective Internal Redox Cyclization: An “Azaenamine” Conjugate Addition

(E)-3-(Hetero)aryl-1-(2-((E)-(indolin-1-ylimino)methyl)phenyl)prop-2-en-1-ones 1 undergo 6-exo-trig cyclization reactions upon treatment with BF3·Me2S in dichloromethane at low temperature to give the tetralones 10 in good yield. This cyclization process can be considered to be an intramolecular Michael-type addition which is accompanied by an internal redox reaction as the indoline fragment is oxidized to indole with simultaneous hydrogen shift to nitrogen atom N1 and the α-carbon atom of the Michael system. The reactions at the iminic centers take place via umpolung of the classical carbonyl reactivity. The reaction is diastereoselective and affords exclusivly 3,4-disubstituted α-tetralones 10 as trans-diastereomers. According to quantum chemical calculations the reactions take place under kinetic control with the trans-diastereomer being the kinetically favored product as it has the lower activation barrier compared to the cis-diastereomer

Imprinting With Phenyl Group Interactions: A Case Study of the Hybrid Sol−Gel Encapsulation of the Complex {Na[Ph₂P(O)−CH₂−P(O)Ph₂]₃}⁺

The sodium complex cation, {Na[Ph2P(O)−CH2−P(O)Ph2]3}+, is used as a guest species in acid-catalyzed aqueous sol−gel processes of tetraethoxysilane and phenyltriethoxysilane. Raman spectroscopy in combination with band assignments from DFT calculations, solid-state NMR, and thermal analyses are applied to study the structural integrity of the sodium complex and to characterize the structural properties of the sol−gel materials. The sodium complex is decomposed at a synthesis pH value of 1, whereas it is encapsulated intact at pH = 4. Calcination removes the complex, and micropores are observed. Phenyl group interactions between the complex surface and the phenyl-functionalized hybrid gel are suggested to take place in the encapsulation process. The spherically shaped sodium complex serves as a model compound for surface interactions between aromatic groups during the genesis of an encapsulated sol−gel hybrid material, and it can be regarded as a soft complex, whose structural stability is of the same order as the interaction energy with its environment

Facile Synthesis of an Unsaturated Spiro Germane by Hydroalumination and Intramolecular 1,1-Carbalumination

Treatment of the tetraethynylgermanium compound Ge(CCC6H5)4 4 with 2 equiv of H−Al[CH(SiMe3)2]2 yielded the addition product Ge(CCC6H5)2[C{AlR2}C(H)C6H5]2 (5, R = CH(SiMe3)2) by reduction of two of its CC triple bonds. Heating of 5 to 260 °C for 10 min gave a unique rearrangement reaction which via intramolecular 1,1-carbalumination afforded the spiro germane 6 (a 3,7-bis[1-phenylmeth-(Z)-ylidene]-4-germaspiro[3,3]hepta-1,5-diene derivative). The molecular structure of 6 comprises two unsaturated 1-germacyclobut-2-ene heterocycles with a joint germanium atom and two exocyclic CC double bonds

A Unique Chlorine–Methyl Exchange Reaction upon Treatment of Dichloroorganogallium Compounds, RGaCl₂, with the Bulky Alkyllithium Derivative LiC(SiMe₃)₃

Reaction of the organogallium chlorides C6H6–n[C(H)C(GaCl2)-SiR3]n (1 to 4; R = Me, Ph) with the bulky alkyllithium derivative Li(THF)2C(SiMe3)3 did not afford the expected alkylgallium chlorides by salt elimination. Instead, compounds (5 to 7) were isolated that had methyl groups attached to gallium, while chlorine atoms moved to silicon to yield Ga(Me)-C(SiMe3)2(SiMe2Cl) moieties. On the basis of quantum chemical calculations the formation of these unprecedented structural motifs is caused by kinetic control involving cyclic transition states as initiating steps. The anticipated, but experimentally not observed products having the intact Ga(Cl)-C(SiMe3)3 subunits (8) were calculated to be thermodynamically favored

Facile Synthesis of an Unsaturated Spiro Germane by Hydroalumination and Intramolecular 1,1-Carbalumination

Treatment of the tetraethynylgermanium compound Ge(CCC6H5)4 4 with 2 equiv of H−Al[CH(SiMe3)2]2 yielded the addition product Ge(CCC6H5)2[C{AlR2}C(H)C6H5]2 (5, R = CH(SiMe3)2) by reduction of two of its CC triple bonds. Heating of 5 to 260 °C for 10 min gave a unique rearrangement reaction which via intramolecular 1,1-carbalumination afforded the spiro germane 6 (a 3,7-bis[1-phenylmeth-(Z)-ylidene]-4-germaspiro[3,3]hepta-1,5-diene derivative). The molecular structure of 6 comprises two unsaturated 1-germacyclobut-2-ene heterocycles with a joint germanium atom and two exocyclic CC double bonds