Thermal transformation of arylamidoximes in the presence of phosphorus ylides. Unexpected formation of 3‐aryl‐5‐arylamino‐1,2,4‐oxadiazoles

The unexpected formation of 3‐aryl‐5‐arylamino‐1,2,4‐oxadiazoles took place, when arylamidoximes reacted thermally with ethoxycarbonylmethylene(triphenyl)phosphorane. Furoxans, nitriles, ureas were also isolated suggesting aryl cyanide oxides as intermediates. 3‐Aryl‐5‐arylamino‐1,2,4‐oxadiazoles were formed via an aryl migration from the carbon atom to the nitrogen atom of the amidoxime, and the structure was further proved from the X‐ray crystal structure of the N‐(4‐bromobenzoyl) derivative.     

Reduced and excited states of (bpym)[PtCl(2)](n)() (bpym = 2,2'-bipyrimidine; n = 1, 2): experiments and DFT calculations

The complexes (bpym)PtCl(2) (1) and the new (micro-bpym)[PtCl(2)](2) (2), bpym = 2,2'-bipyrimidine, were synthesized and, in the case of 1, crystallized in solvent-free form for X-ray diffraction. The molecules 1 exhibit two different kinds of stacking motifs in the crystal with an interstack CH--N interaction. Complexes 1 and 2 were found to be sufficiently soluble for cyclic voltammetry, spectroscopy (absorption and emission), and spectroelectrochemical studies (UV-vis, EPR). As a result of single or double coordination of the strongly sigma-accepting [PtCl(2)] fragment to bpym, the paramagnetic anions 1(*)(-)() and 2(*)(-)() and the dianions 1(2-) and 2(2-) could be reversibly generated, despite the presence of metal-halide bonds. DFT calculations of A((195)Pt) and g tensor components confirm that the singly occupied MOs of the monoanionic species have mainly pi(bpym) character with nonnegligible platinum d orbital participation. The assignments of the electronic absorption and emission and resonance Raman spectra for both complexes are supported by DFT calculations.     

PHOTOTHROMBOSIS USING TWO DIFFERENT PHTHALOCYANINE ADMINISTRATION ROUTES: CONTINUOUS I.V. INFUSIO versus BOLUS I.V. INJECTION*

Chloraluminum sulfonated phthalocyanine was administered in 22 albino rabbits either by means of bolus i.v. (intravenous) injection (6 mg/kg) or as continuous i.v. infusion. Eight animals were used for the comparison of plasma phthalocyanine change as a factor of time, using the two administration methods. Photothrombosis of corneal neovascularization was carried out in the remaining 14 animals either after bolus phthalocyanine injection or after continuous i.v. infusion. Irradiation of the right eye's vessels started 10 min after the injection in the bolus group and 35 min after initiation of infusion in the continuous infusion group. The vessels of each animal's left eye were irradiated 1 h after the irradiation of the right eye. The initial peak of phthalocyanine concentration after bolus injection was followed by a rapid decrease of plasma levels. In the continuous infusion group,30–40 min after the initiation of infusion, plasma phthalocyanine concentration reached a plateau that remained stable for the rest of the80–90 min of infusion. Using bolus injection, a significant decrease of phthalocyanine concentration was accompanied by a significant increase of irradiation time necessary for neovascularization thrombosis in the two eyes. Irradiation time as well as phthalocyanine concentration did not differ between the two eyes using continuous infusion. Vascular photosensitivity seemed to be higher using continuous i.v. infusion of phthalocyanine. Continuous i.v. infusion represents an interesting alternative to bolus injection for phthalocyanine-mediated corneal neovascularization photothrombosis.     

Suzuki-Miyaura cross-coupling reaction of aryl bromides and chlorides with phenylboronic acid under aerobic conditions catalyzed by palladium complexes with thiosemicarbazone ligands

For the first time, palladium complexes with salicylaldehyde thiosemicarbazones were applied as catalyst precursors to the Suzuki-Miyaura reaction. These air and moisture stable phosphine-free systems efficiently catalyze the cross-coupling of aryl bromides and chlorides (from electron rich to electron poor) with phenylboronic acid in DMF/H₂O at 100 °C for 24 h, using Na₂CO₃ as base, without addition of free ligand or any promoting additive, and under aerobic conditions no significant homocoupling of phenylboronic acid to unsubstituted biphenyl was observed.     

Rapid synthesis of 2,3-disubstituted-quinazolin-4-ones enhanced by microwave-assisted decomposition of formamide

An efficient methodology for the preparation of a series of 2,3-disubstituted-quinazolin-4(3H)-ones is described via a three step reaction from anthranilic acid. The obtained results also reveal that microwave-assisted rapid decomposition of formamide under controlled conditions of power, temperature and time is a very convenient source of ammonia for the synthesis of 2-substituted-quinazolin-4(3H)-ones and other rings.     

Synthese,Kristallstruktur und thermischer Abbau von Mg(H2O)6[B12H12] · 6 H2O

Synthesis, Crystal Structure, and Thermal Decomposition of Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O By reaction of an aqueous solution of the free acid (H₃O)₂[B₁₂H₁₂] with MgCO₃ and subsequent isothermic evaporation of the resulting solution to dryness, colourless, bead‐shaped single crystals of the dodecahydrate of magnesium dodecahydro closo‐dodecaborate Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O (cubic, F4₁32; a = 1643.21(9) pm, Z = 8) emerge. The crystal structure is best described as a NaTl‐type arrangement in which the centers of gravity of the quasi‐icosahedral [B₁₂H₁₂]^2— anions (d(B—B) = 178—180 pm, d(B—H) = 109 pm) occupy the positions of Tl^— while the Mg²⁺ cations occupy the Na⁺ positions. A direct coordinative influence of the [B₁₂H₁₂]^2— units at the Mg²⁺ cations is however not noticeable. The latter are octahedrally coordinated by six water molecules forming isolated hexaaqua complex cations [Mg(H₂O)₆]²⁺ (d(Mg—O) = 206 pm, 6×). In addition, six “zeolitic” water molecules are located in the crystal structure for the formation of a strong O—H^δ+···^δ—O‐hydrogen bridge‐bonding system. The evidence of weak B—H^δ—···^δ+H—O‐hydrogen bonds between water molecules and anionic [B₁₂H₁₂]^2— clusters is also considered. Investigations on the dodecahydrate Mg[B₁₂H₁₂] · 12 H₂O (≡ Mg(H₂O)₆[B₁₂H₁₂] · 6 H₂O) by DTA/TG measurements showed that its dehydration takes place in two steps within a temperature range of 71 and 76 °C as well as at 202 °C, respectively. Thermal treatment eventually leads to the anhydrous magnesium dodecahydro closo‐dodecaborate Mg[B₁₂H₁₂].     

Microwave-promoted Suzuki-Miyaura cross-coupling of aryl halides with phenylboronic acid under aerobic conditions catalyzed by a new palladium complex with a thiosemicarbazone ligand

A new air- and moisture-stable palladium complex with salicylaldehyde N(4)-hexamethyleneiminylthiosemicarbazone has been synthesized. According to its crystal structure, the metal is bonded to 2 equiv monoanionic thiosemicarbazone moieties in a N,S-bidentate fashion, forming two five-membered chelate rings, while additional intramolecular bonds stabilize the structure. In contrast to other palladium complexes with thiosemicarbazones, this complex was inactive towards the Suzuki-Miyaura coupling under aerobic conditions, by conventional heating. On the other hand, microwave irradiation promoted the effective catalytic activity of the complex for the coupling of aryl bromides and chlorides with phenylboronic acid in DMF/H₂O, under aerobic conditions, with turnover numbers of up to 37,000.     

Olefin metathesis: remote substituents governing the stereoselectivity of 11-membered-ring formation

[reaction: see text] Stereospecific RCM reaction of 7 (R1 = Me) results in the formation of (Z)-11-membered macrocycle 9c. Cascade RCM/ROM/RCM transformation of 7 (R1 = H) affords the thermodynamically more stable spirocycle product 12.     

Ene reaction of singlet oxygen,triazolinedione, and nitrosoarene with chiral deuterium-labeled allylic alcohols: the interdependence of diastereoselectivity and regioselectivity discloses mechanistic insights into the hydroxy-group directivity

The ene reaction of singlet oxygen ((1)O(2)), triazolinedione (TAD), and nitrosoarene, specifically 4-nitronitrosobenzene (ArNO), with the tetrasubstituted 1,3-allylically strained, chiral allylic alcohol 3,4-dimethylpent-3-en-2-ol (2) leads to the threo-configured ene products in high diastereoselectivity, a consequence of the hydroxy-group directivity. Hydrogen bonding favors formation of the threo-configured encounter complex threo-EC in the early stage of ene reaction. For the analogous twix deuterium-labeled allylic alcohol Z-2-d(3), a hitherto unrecognized dichotomy between (1)O(2) and the ArNO and TAD enophiles is disclosed in the regioselectivity of the tetrasubstituted alcohol: Whereas for ArNO and TAD, hydrogen bonding with the allylic hydroxy group dictates the regioselectivity (twix selectivity), for (1)O(2), the cis effect dominates (twin/trix selectivity). From the interdependence between the twix/twin regioselectivity and the threo/erythro diastereoselectivity, it has been recognized that the enophile also attacks the allylic alcohol from the erythro pi face without assistance by hydrogen bonding with the allylic hydroxy functionality.     

The monotone follower problem in stochastic decision theory

We consider the problem of optimally tracking the random demandx+w _t, w. Brownian motion, by a nondecreasing process. adapted to the Brownian past, so as to minimize the expected lossE ₀ ^T (x+w_t–_t)dt. The decision problem is reduced to a free boundary one, and the latter is studied and solved for a large class of cost functions().This research was supported in part by the Air Force Office of Scientific Research, under AF-AFOSR 77-3063.