Potassium Hydride In Tetrahydrofuran Research Articles

New main-group and early transition-metal complexes of mono-pendant arm triazacyclononane ligands

A family of new Group 3, Group 13 and early transition metal complexes of the previously described monoanionic, pendant arm macrocyclic ligands La, Lb and Lc are described where HLa = (3,5-dimethyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane 1a, HLb = (3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane 1b, and HLc = (3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-dimethyl-1,4,7-triazacyclononane 1c. The ligand precusors 1a–c are quantitatively converted to the corresponding new potassium salts KLa, KLb and KLc2a–c by reaction with potassium hydride in tetrahydrofuran (THF). An improved synthesis of HLc1c is also reported. Reaction of KLa–c with Group 13 metal salts MCl3 (M = Al, Ga or In) gives monomeric derivatives [M(κ4-La–c)Cl2] 3–5 in good yields. The crystal structure of [In(κ4-Lb)Cl2] 5b has been determined and confirms the six-coordinate, cis-dichloride structures proposed for these complexes. Reaction of KLa–c with TlCl3 gives the asymmetric, binuclear analogues [Tl(κ4-La–c)Cl2]26a–c. Reaction of [Al(κ4-Lc)Cl2] 3c with AlCl3 gives the unstable, five-coordinate cation [Al(κ4-Lc)Cl]+ as its AlCl4− salt 8c. Reaction of KLa–c with MCl3 (M = Sc or Y) or [MCl3(THF)3] (M = Ti, V, Cr) in THF gives generally good yields of the Group 3 cis-dichloride derivatives [M(κ4-L1a–c)Cl2] (M = Sc 8a–c or Y 9b,c) and the early transition metal analogues [M(κ4-Lb,c)Cl2] (M = Ti 10b,c, V 11b,c or Cr 12b,c). Reaction of HL1a–c with TlOEt yields the monomeric, four-coordinate thallium(I) derivatives [Tl(κ4-L1a–c)] 13a–c as confirmed by the X-ray crystal structures of 13b and 13c. p

Synthesis, Structure, and Reactivity of Potassium Pyrazolato Complexes: The First Structurally Documented eta(2)-Pyrazolato Coordination by a Main Group Metal.

Several (pyrazolato)potassium complexes have been prepared by deprotonation of the parent pyrazoles with potassium hydride in tetrahydrofuran. A crystal structure of one derivative shows a hexameric formulation, with each potassium atom bonded to the nitrogen atoms of one pyrazolato ligand in an η2-fashion and to the nitrogen atoms of two adjacent pyrazolato ligands with η1-interactions. The utility of these complexes in the synthesis of new pyrazolato complexes is demonstrated.

Neighboring Group Effects in Intramolecular Aldol Condensations. Rate Enhancement by gamma Substituents(1).

The O-acetyl dieneol 1b, obtained from the Grignard addition of 2-(2-bromoethyl)-1,3-dioxolane to 2,4-hexadienal via 1a, and followed by an acetylation, was treated with maleic anhydride to give the crystalline Diels-Alder adduct 2b with good stereoselectivity. The acetal of 2b was selectively hydrolyzed to the acetoxy aldehyde 3b. This was treated with potassium hydride in tetrahydrofuran. A stereoselective intramolecular Aldol reaction resulted in the formation of the tricyclic lactone 4b. However, attempts to achieve an Aldol condensation under similar reaction conditions with the analogous aldehyde 3c, lacking the acetoxy group, failed, giving back the starting material 3c. On the other hand, the methoxy aldehyde 3d was cyclized to the tricyclic compound 4d.

Anionic polymerization of carbazolyl‐substituted oxiranes initiated by potassium alkalide, potassium tert‐butoxide and potassium hydride

AbstractThe influence of the kind of initiating system and the addition of a crown ether on the anionic polymerization of oxiranes with a carbazoyl substituent is described. Potassium alkalide, potassium tert‐butoxide and potassium hydride were used as initiators. Selecting a suitable initiator and crown ether concentration, carbazolyl‐containing polymers with polymerization degrees from 4 to 60 can be produced. Using a suspension of potassium hydride in tetrahydrofuran, polymers with relatively high molar masses were obtained.

Metal-stabilized carbanions

Abstract Rate constants have been measured for the α-metallation of some arylmethanes, of 5 H -dibenzo[ a,d ]cycloheptene and its dihydro derivative, free and complexed with tricarbonylchromium, by potassium hydride in tetrahydrofuran in the presence of 18-crown-6 ether. The stable solutions of the complexed anions have been studied by 13 C NMR spectroscopy. With the free ligands the kinetic acidity depends upon the structure to a great extent, but in the corresponding complexes the rates of metallation do not vary appreciably. On the basis of the 13 C chemical shift data a close similarity is suggested between the electronic structures of the arylmethyl and dibenzotropenyl anions which would account for their very similar metallation rates.

Conjugate addition of lithium phenylthio- and cyano-[2-(4-chlorobut-1-enyl)]cuprate to cyclic enones. An efficient methylenecyclopentane annulation process

Reaction of the cyclic enones (6)–(11) with the structurally interesting cuprate reagent (2) and (3) provides very good yields of the conjugate addition products (12)–(17); treatment of the latter substancesh with potassium hydride in tetrahydrofuran affords the methylenecyclopentane annulation products (18)–(23), respectively.

Macroexpansion methodology : Medium ring synthesis based on an eight unit ring expansion process

Treatment of 1,2-( E,E)-di(1-buta-1,3-dienyl)cyclohexanol ( 21) with potassium hydride in tetrahydrofuran at room temperature resulted in the facile formation of a 14-membered ring dienolate which on kinetic protonation provided cyclotetradeca-3,5,7-trien-1-one. This novel rearrangement which provides the basis for an efficient, eight unit ring expansion method was also observed when 5,8-dimethyl-5-hydroxy-1,3,7,9-decapentaene ( 28), the acyclic analogue of 21, was treated with potassium hydride in tetrahydrofuran. Methodology for the preparation of 21 and 28 including the preparation of 1-lithio-1,3-butadiene is also described.

ChemInform Abstract: (1.3) SHIFTS OF POTASSIUM ALKOXIDES‐ THE BICYCLO(3.2.0)HEPTENE‐NORBORNENE TRANSFORMATION

AbstractDas exo‐Bicycloheptenol (I) wird als Kaliumsalz zu einem 67:8‐Gemisch der Alkohole (II) und (III) isomerisiert.

Facile reaction of potassium hydride with trialkylboranes, a convenient general synthesis of simple and hindered potassium trialkylborohydrides under exceptionally mild conditions

The reaction of potassium hydride in tetrahydrofuran with simple and hindered trialkylboranes proceeds readily at 25°C (<0.5 h) with the formation of the corresponding trialkylborohydrides. Even some highly hindered trialkylboranes react smoothly under these conditions. This reaction provides a convenient synthesis in high yields of such hindered and highly hindered potassium trialkylborohydride under very mild reaction conditions.

Chain elongation of sugars with ethyl isocyanoacetate

Addition of ethyl isocyanoacetate to 3- O-benzyl-1,2- O-isopropylidene-α- D- ribo-pentodialdo-1,4-furanose in ethanolic sodium cyanide gave two oxazolines that were hydrolysed during chromatography to two isomeric ethyl 3- O-benzyl-6-deoxy-6-formamido-1,2- O-isopropylidene-heptofuranuronates. Similarly, 1,2- O-isopropyl-idene-3- O-methyl-α- D- xylo-pentodialdo-1,4-furanose gave the 3- O-methyl-heptofuranuronates 7 and 11. Reduction of 7 and 11 gave N-methylamino esters that exhibited Cotton effects from which the configurations at C-6 of 7 and 11 were deduced. The chiralities at C-5 of 7 and 11 were established by tetrahydropyranlation of 7 and 11, followed by consecutive treatment with bis(2-methoxyethoxy)aluminium hydride, periodate, sodium borohydride, and dilute acid, to give 1,2- O-isopropylidene-3- O-methyl-α- D-glucofuranose and its β- L- ido epimer, respectively. Attempts to methylate HO-5 of 7 and 11 resulted in elimination. On formylaminomethylenation (ethyl isocyanoacetate and potassium hydride in tetrahydrofuran), 3- O-benzyl-1,2- O-isopropylidene-α- D- ribo-pentodialdo-1,4-furanose and its 3- O-methyl-α- D- xylo epimer each gave ( E)- and ( Z)-mixtures of alkenes that were hydrogenated to give mixtures of 5,6-dideoxy-6-formamido-heptofuranuronates.

1,3] Shifts of potassium alkoxides: the bicyclo[3.2.0]heptene–norbornene transformation

exo-Bicyclo[3.2.0]hept-2-en-7-ol can be isomerized to exo-norbornenol on treatment with potassium hydride in tetrahydrofuran at room temperature.

Metallation of weak hydrocarbon acids by potassium hydride–18-crown-6 polyether in tetrahydrofuran and the relative acidity of molecular hydrogen

Potassium hydride in tetrahydrofuran in the presence of 18-crown-6 polyether is capable of metallating the hydrocarbons triphenylmethane, diphenylmethane, di-p-tolymethane (to completion), and di-2,4-xylyl-methane (partial completion); the results allow an estimate of the relative acidity of hydrogen with respect to the hydrocarbons studied.