A Regioselective Synthesis of Benzopinacolones through Aerobic Dehydrogenative α‐Arylation of the Tertiary sp3 CH Bond of 1,1‐Diphenylketones with Aromatic and Heteroaromatic Compounds

A regioselective synthesis of symmetrical and unsymmetrical benzopinacolones through aerobic dehydrogenative α‐arylation at the tertiary sp³ C?H bond of substituted 1,1‐diphenylketones with aromatic and heteroaromatic compounds, in the presence of K₂S₂O₈ in CF₃COOH at room temperature, is described. The reaction is proposed to go via a carbocation intermediate, which could be generated directly from cleavage of the sp³ C?H bond of 1,1‐diphenylketone. Subsequent α‐arylation was achieved at the methene sp³ carbon atom of the substituted ketone. A variety of substituted aromatic and heteroaromatic compounds were compatible with this reaction. In addition, benzopinacolones were converted into sterically hindered, tetrasubstituted alkenes and polycyclic aromatic compounds.     

An oscillator-amplifier distributed feedback dye laser system,pumped by a single TEA N2 laser

In this paper we describe a simple and inexpensive Distributed Feedback Dye Laser (DFDL) system for picosecond pulse generation. This system consists of an oscillator-amplifier DFDL, either in the grating or in the prism configuration: both stages are pumped by a single TEA nitrogen laser with improved beam quality. Single pulses having duration of 26 ps are obtained at a frequency up to 100Hz; the overall pulse-to-pulse stability is, at the maximum frequency, of about 25%. This system is particularly well-suited for time-resolved fluorescence microscopy studies where short tunable laser pulses of low energy are required.     

Ene reaction of arynes with alkynes

Arynes, generated in situ from ortho-silylaryl triflates, undergo ene reaction with alkynes possessing propargylic hydrogen in the presence of KF/18-crown-6 in THF at room temperature to give substituted phenylallenes. Various terminal and internal alkynes as well as different arynes can be used to give the corresponding phenylallenes in good to moderate yields. The reaction of alkyne without propargylic hydrogen gave an acetylenic C-H addition product (a phenylalkyne) and a dehydro Diels-Alder product (a phenanthrene).     

Laser properties of a conjugate polymer (MEH-PPV) in the liquid-excimeric state

We have studied the amplified spontaneous-emission characteristics (ASE) of conjugated poly[2-methoxy-5-(2-ethylhexyloxy)1,4-phenylenevinylene] MEH-PPV in a few organic solutions. The ASE of MEH-PPV appears to arise from its excimeric state. This is perhaps the first report, to the best of our knowledge, on an excimeric-liquid state laser. MEH-PPV in solutions of benzene or tetrahydrofuran (THF) was pumped by the second and third harmonics of an Nd:YAG (532 and 355 nm) for different pump-pulse energies. The ASE of MEH-PPV was compared with the conventional laser dyes Rhodamine B (Rh B) and Rhodamine 6G (Rh 6G). The most important and distinguishing features are: (a) MEH-PPV has a four-times better photochemical stability than Rh B or Rh 6G; (b) the threshold and concentration for the laser action in MEH-PPV is far less than Rh B or Rh 6G.     

Photophysics of TICT states of 7-diethylamino-4-methyl coumarin dye by energy transfer techniques

Coumarin 1 exhibited dual amplified spontaneous emission (ASE) in certain solvents under nitrogen laser excitation. These emissions are known as normal and anomalous emissions. The anomalous emission corresponds to TICT state and it does not have a corresponding fluorescence peak. Energy transfer techniques have been used to study the photophysics of TICT states and the characteristics of dual ASE bands of the dye coumarin 1.     

Solid state structure of the hydrated potassium thiocyanate complex of benzodinaphthopyridino 21-crown-7, C37H31NO6·KSCN·H2O (1 : 1 : 1)

Single crystal X-ray analysis of the hydrated KSCN complex of benzodinaphthopyridino-21-crown-7 (1) (1 : 1 : 1) is reported. Crystals of the complex are orthorhombic,Pnma, with = 16.946(4),b = 22.298(4),c = 10.390(8) Å andD _c = 1.184 g cm^–1,Z = 4. The host macroring (1) has a mirror symmetry and exists in a so-called dentists chair conformation. The cation (K^–) is coordinated to all the six ether oxygen atoms and also weakly to the pyridine N atom. The SCN^– anion group has a statistical type of disorder with opposite orientations of S and N such that nitrogen and sulphur are coordinated to K⁺. Packing of the host molecules is in columns to form quasi channels with K⁺, SCN^–, and H₂O being located inside the stacks. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82132 (9 pages).     

Nickel‐Catalyzed Mizoroki–Heck‐ versus Michael‐Type Addition of Organoboronic Acids to α,β‐Unsaturated Alkenes through Fine‐Tuning of Ligands

Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br₂], ZnCl₂, and H₂O in CH₃CN at 80 °C to give the corresponding Mizoroki–Heck‐type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael‐type addition was achieved in a very selective manner. Thus, various p‐ and o‐substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH₃CN at 80 °C for 12 h catalyzed by Ni(acac)₂, P(o‐anisyl)₃, and K₂CO₃ to give the corresponding Michael‐type addition products in excellent yields. However, for m‐substituted arylboronic acids, the yields of Michael‐type addition products are very low. The cause of this unusual meta‐substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m‐substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki–Heck‐type products and dry reaction conditions for Michael‐type addition products. Possible mechanistic pathways for both addition reactions are proposed.