Microwave Assisted Selective Oxidation of Benzylic Alcohols with Calcium Hypochlorite under Solvent-Free Conditions

Summary.  A remarkably fast microwave assisted selective oxidation of benzylic alcohols with calcium hypochlorite under solvent-free conditions is described. Received August 28, 2000. Accepted September 21, 2000     

A Mild Deoxygenation of Heteroaromatic N-Oxides by Formamidinesulfinic Acid

Summary.  Various heteroaromatic N-oxides were efficiently deoxygenated to the corresponding bases under mild conditions using formamidinesulfinic acid (thiourea S,S-dioxide). Received March 24, 2000. Accepted April 18, 2000     

Ammonium Chlorochromate Adsorbed on Montmorillonite K-10: Oxidative Deprotection of Tetrahydropyranyl Ethers Using Microwaves in a Solventless System

Summary.  Tetrahydropyranyl ethers were rapidly and selectively oxidized to the corresponding carbonyl compounds by clay supported ammonium chlorochromate under solvent free conditions using microwaves. Received July 25, 2000. Accepted September 7, 2000     

Synthesis of Enantiopure Chiral Perhydrobenzimidazole and Hexahydroquinoxaline Derivatives

Summary.  Starting from 2-anilino-2-ethoxy-3-oxothiobutyric acid anilides and (R, R)-or (S, S)-trans-1,2-diaminocyclohexane, chiral C2-disubstituted perhydrobenzimidazole and trans-4a,5,6,7,8,8a-hexahydroquinoxaline derivatives were obtained depending on the polarity of the solvent. Received April 10, 2000. Accepted May 2, 2000     

Solvent-Free Aminoalkylation of Phenols and Indoles Assisted by Microwave Irradiation

Summary.  Phenols and indoles were aminoalkylated in a solvent-free and environmentally friendly Mannich reaction on acidic alumina assisted by microwave irradiation in good overall yields. Received November 10, 2000. Accepted December 6, 2000     

A Sequence of Aldol Condensations and a Michael Addition Giving a Cyclohexenone Ring System

Summary.  The reaction of 1,5-diphenylpentanetrione, 4-chlorobenzaldehyde, and acetone in the presence of methylamine resulted in 2,6-dibenzoyl-5-(4-chlorphenyl)-3-methyl-cyclohex-2-en-1-one, which was formed by a sequence of a Knoevenagel reaction, an aldol condensation, and a Michael addition in a one-pot reaction. Received August 16, 2000. Accepted September 8, 2000     

Chemoselective Preparation of Oximes, Semicarbazones, and Tosylhydrazoneswithout Catalyst and Solvent

Summary.  A simple and versatile method for the synthesis of oximes, semicarbazones, and tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented. Received June 28, 2000. Accepted (revised) August 25, 2000     

An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

Summary.  Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge. Received July 17, 2000. Accepted July 20, 2000     

A New Chiral Director for the Highly Diastereoselective Borane Reductionof Steroid-20-ones

Summary.  The synthesis of a new chiral boroxazolidine was achieved which was used to control the stereochemistry of the borane reduction of the 20-keto group of steroids. The otherwise hardly accessible 20α-(20S)-alcohol can thus be prepared in a yield of 91%. Received April 10, 2000. Accepted (revised) May 2, 2000     

Novel Fused Heterocycles: Synthesis and Activity of 5,6-Dihydro-7-thia-1,3,3a,5-tetraazainden-4-one and 1-Thia-3,4a,9-triazafluoren-4-one Derivatives

Summary.  Thiatetraazaindenone derivatives were synthesized by reaction of 3-substituted 1,2,4-triazole-5-thiols with N-substituted N-chloromethyl carbamoyl chlorides. A series of thiatriazafluorenone derivatives were also prepared by reaction of benzimidazole derivatives with the same substrate. Some of the new compounds show fungicidal, herbicidal, and insecticidal activity. Received February 14, 2000. Accepted (revised) April 11, 2000     

Synthesis of a Model for Phycocyanin with Respect to the Acid-Base Chemistry between Protein and Chromophore

Summary.  Earlier investigations have shown that the cysteine adduct of phycocyanobilin dimethylester qualifies for intramolecular protonation [1]. In this context, the -Cys-Ala-Phe-Asp-tetrapeptide adduct of phycocyanobilin dimethylester was synthesized and examined for its protonation properties with respect to the zwitterionic interaction between chromophore and protein. Received March 15, 2000. Accepted March 21, 2000     

Regioselective Synthesis ofPyrano[3,2-f]quinolin-2(7H)-onesand Furo[3,2-f]quinolin-2-ones

Summary.  A simple and efficient synthesis of the hitherto unreported ring systems pyrano[3,2-f]quinolin-2(7H)-one and furo[3,2-f]quinolin-2-one was accomplished via a thermal [3,3]-sigmatropic rearrangement. Received March 7, 2000. Accepted May 4, 2000     

Zeolite HY and Silica Gel as New and Efficient Heterogenous Catalysts for the Synthesis of Triarylimidazoles under Microwave Irradiation

Summary.  Zeolite HY and silica gel efficiently catalyzed the three component condensation of benzil, benzaldehyde derivatives, and ammonium acetate under solvent-free conditions and microwave irradiation. Received February 22, 2000. Accepted (revised) March 22, 2000     

Synthesis and Characterization of a Phthalocyanine-Porphyrazine Hybridand its Palladium(II) Complex

Summary.  A phthalocyanine-porphyrazine hybrid molecule composed of three phthalonitrile units and one maleonitrile moiety was prepared by cyclomerization of the reactants in the presence of magnesium butoxide. Two thioether groups fused to β-pyrrol positions were complexed with PdCl₂. The compounds were characterized by ¹H NMR, IR, and UV/Vis spectroscopy as well as elemental analysis. Received May 23, 2000. Accepted June 26, 2000     

Reductive Coupling of Carbonyl Compounds to Pinacols with Zinc in THF-Saturated Aqueous Ammonium Chloride

Summary.  In the presence of metallic zinc, aldehydes and ketones experience reductive coupling in tetrahydrofuran-saturated aqueous ammonium chloride (5:3) to afford the corresponding pinacols in moderate to high yields. Received October 23, 2000. Accepted (revised) December 12, 2000     

Novel Functional Fullerene Materials: Fullerenes as Energy Acceptors

Summary.  Fullerene derivatives exhibit absorption throughout the UV/Vis region up to 750 nm. This feature is important for easy excitation. Once excited, fullerenes may become both electron and energy acceptors. The distinction between these two pathways depends strongly on the partner involved (donor) and on the conditions employed (solvent, etc.). Received June 23, 2000. Accepted July 7, 2000     

Asymmetric Allylic Substitution Reactions with a Xylophos-Pd Catalyst

Summary.  The chiral diphosphine ligand xylophos (1) was tested as an auxiliary in palladium catalyzed allylic substitution reactions. Whereas its activity was found to be generally good only in the case of 1,3-diphenylprop-2-en-1-yl acetate, a fair level of asymmetric induction was achieved with sodium dimethyl malonate (83%ee) and benzylamine (66%ee) as nucleophiles. Received June 13, 2000. Accepted July 3, 2000     

Novel Ring Systems in Morphinoides II [1]: C8,17-Ethano-Bridged 4,5-Epoxyhasubanans

Summary.  Claisen-Eschenmoser rearrangement of the 9,10-saturated derivative of 4,5-epoxyhasubanan-6β-ol affords the 8β-substituted amide which can be converted to the polycyclic quaternary ammonium salt 7 with an indolizidine substructure. An N-demethylation step with triethylborohydride leads to three products in accordance with the different possible positions of attack of the hydride ion to the strained ring system. Received March 17, 2000. Accepted April 13, 2000     

An Anionic Mn(III) Ethyleneglycolate Complex

Summary.  The crystal structure of consists of individual layers in which the anionic complexes form strings of vertex-sharing octahedral units. These strings are interconnected by units to form layers via Na-Cl and Na-O interactions. An outstanding feature of the compound are the unusually strong Jahn-Teller elongated trans- octahedra. Received April 25, 2000. Accepted May 8, 2000     

Spectroscopic Study of the Conformation of 2-Anilino-2-ethoxy-3-oxothiobutyric Acid Anilides

Summary.  An NMR study of the equilibriummixture of two conformers of 2-anilino-2-ethoxy-3-oxothiobutyric acid anilides 3 allows to estimate their population ratio in solvents of increasing polarity. X-Ray analysis as well as IR spectroscopy confirmed that the conformer present in the solid state is stabilized by two hydrogen bonds. The structural basis of the second conformer observed in solution is the 1,4-type S⋯O interaction between the sulfur of the thioanilide moiety and the oxygen of the ethoxy group with a distance of 2.878 ?. Received May 29, 2000. Accepted (revised) July 14, 2000