Intramolecular silyl migration in the singlet oxygenation of 2-methyl-5-trimethylsilylfuran

Tetraphenylporphyrin-sensitized photooxygenation of 2-methyl-5-trimethylsilylfuran ($\text{4}$) affords quantitatively trimethylsilyl 2-oxo-4-pentenoate ($\text{5}$), presumably via intramolecular Baeyer-Villiger rearrangement of the intermediary dioxirane ($\text{3a}$).     

Indolopyridines with a hetero atom at a position of fusion. 5. Catalytic synthesis of indolo[2,1-a]isoquinoline by pyrolysis of benzylisoquinolines

High-temperature heterocyclization of -benzylisoquinolines on oxide-type catalysts gave angular indolo[2,1a] isoquinoline.For Communication 4 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 79–82, January, 1994.     

Semiclassical study of collision-induced predissociation: Comparison of the Landau-Zener model with the method of analytic continuation

Semiclassical calculations are carried out by two methods for the problem of collision-induced predissociation of electronically excited I₂. The first method is that of surface-hopping with the Landau-Zener model. The second method is similar to surface-hopping, except that analytic continuation of the adiabatic potential energy surfaces replaces the Landau-Zener model. Results of the calculations by the two methods compare favorably with each other and with experiment. The possible advantages of the second method are discussed.Camille and Henry Dreyfus Teacher-Scholar, Alfred P. Sloan Research Fellow.     

Generation and fate of free radicals of Δ2-oxazolin-5-ones

The reaction of Δ² -oxazolin-5-ones 1a and 1b with nickel peroxide in benzene produces the corresponding 4,4-dehydrodimers 5a and 5b as the main products in yields over 75%. Under the same conditions, the 2-aryl -4-methyl - Δ²-oxazolin-5-ones 1c, 1d and 1e yield five products. In the case of 1c, the constituents of the product mixture were separated and identified as two 4,4-dehydrodimers ( meso and d] pair isomers) 5c and 5c', (40.7%), 2,4-dehydrodimer 6c (34.9%), acetylanisoylimide 8c (8.5%) and anisamide (15.9%). Adequate mechanistic schemes are discussed to account for the products formed.     

Structural investigation of 3,5‐disubstituted isoxazoles by 1H‐nuclear magnetic resonance

HIV‐1 integrase (IN) is a very promising and validated target for the development of therapeutic agents against AIDS. In an effort to design and synthesize biological isosteric analogs of β‐diketoacid‐containing inhibitors of IN, we prepared a series of substituted isoxazole carboxylic acids. Several of these compounds inhibited catalytic activities of purified IN at micromolar concentration range. With an aim to prepare a large number of analogues based on the isoxazole pharmacophore we focused our study on a series of 3,5‐disubstituted isoxazole isomers. For a rapid structural analysis we discovered a convenient ¹H‐nmr method for distinguishing between isomeric structures based on their H‐4 assignments. This “finger print” approach to isomer identification will be useful in combinatorial chemistry settings where a mixture can be further derivatized.     

New aspects in the reaction of azomethines with cyclic CH-acidic compounds

Summary Treatment of substituted benzylidene anilines1 a – df with cyclic CH-acidic compounds2a–m in ethanol at room temperature yields in additon/elimination reactions the corresponding arylidene derivatives4 and the 2:1 adducts5. The addition products3, which are formed as intermediates, could not be isolated in any case. The donor/acceptor effect of the substituents on the benzylidene moiety influences to a significant extent the reactivity towards the azomethine carbon.

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Neue Aspekte der Reaktion von Azomethinen mit cyclischen CH-aciden Verbindungen

Zusammenfassung Bei der Umsetzung der substituierten Benzylidenaniline1 a – f mit den cyclischen CH-aciden Verbindungen2 a – m in Ethanol bei Raumtemperatur erhält man in Additions/Eliminierungsreaktionen die Arylidenderivate4 und die 2:1-Addukte5. Die als Intermediat gebildeten Additionsprodukte3 konnten in keinem Fall isoliert werden. Die Donor-bzw. Acceptorwirkung der Substituenten am Benzylidenrest beeinflußt maßgebend die Reaktivität am Azomethinkohlenstoff.

     

Preparation and spectroscopic studies of some cyclic urea adducts of triphenyl-tin and -lead halides

1,3-Dimethyl-2-imidazolidinone (dimethylethylene urea, DMEU) and 1,3-di- methyl-3,4,5,6-tetrahydro-2(IH)-pyrimidinone (dimethylpropylene urea, DMPU) adducts of the type Ph₃SnX·L (X = Cl, Br and I), Ph₃PbX·L (X = Br, I), 3Ph₃PbCl·2DMEU and 2Ph₃PbCl · DMPU have been prepared and characterized. Assignments are made for ν(CO) and ν(CN) frequencies in the IR, and for skeletal frequencies observed in both the IR and Raman spectra in the range 400 to 100 cm^?1 Infrared measurements show that the adducts are bound through the carbonyl oxygen, and are highly dissociated in dichloromethane solution. ¹H and ¹¹⁹Sn or ²⁰⁷Pb NMR measurements reveal that ligand exchange, fast on the NMR time scale, occurs in solution. Coordination of the ligand causes a large upfield shift in the ¹¹⁹Sn or ²⁰⁷Pb resonances, but Ph₃MI · L have shifts similar to those for the parent iodides, indicating almost complete dissociation. Thermodynamic parameters are reported for the dissociation of Ph₃SnX · DMPU (X = Cl, Br) in CH₂Cl₂ solution.     

New cis-clerodane diterpenoids from Croton schiedeanus

The acid fraction of extracts from the aerial part of Croton schiedeanus afforded six cis-clerodane type diterpenoids. Two of them (1 and 4) are new natural compounds. Structural elucidation was achieved on the basis of their spectral data.     

PCDD, PCDF, and PCB contamination of air and inhalable particulate in Rome

Summary The isomer specific determination of PCDD, PCDF and PCB was carried out on samples of air and inhalable particulate from Rome. Samples were taken daily for six months and pooled to yield two samples per month. Normal PCDD+PCDF concentrations expressed in TEQ ranged from 48 to 87 fg/m³, while total PCB ranged from 0.1 to 1.4 ng/m³. The 2, 3, 7, 8-substituted PCDD and PCDF congener pattern is shown together with the PCB congener pattern.     

Diphosphacarbollide analogues of the C5H5- anion: isolation of the nido-di- and triphosphacarboranes 7,8,9-P2CB8H10, [7,8,9-P2CB8H9]-, [7,8,10-P2CB8H9]-, and 7,8,9,10-P3CB7H8

Treatment of a solution of excess PCl(3) and PS (PS = "proton sponge" = 1,8-dimethylamino naphthalene) with arachno-4-CB(8)H(14) (1) in CH(2)Cl(2), followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven-vertex diphosphacarbaborane nido-7,8,9-P(2)CB(8)H(10) (2) (yield 34%) as the main product. Other products isolated from this reaction were the phosphacarboranes nido-7,8,9,10-P(3)CB(7)H(8) (3) (yield 5%) and closo-2,1-PCB(8)H(9) (4) (yield 15%). Compound 2 can be deprotonated by PS in CH(2)Cl(2) or NaH in diethyl ether to give the [nido-7,8,9-P(2)CB(8)H(9)](-) (2(-)()) anion, which gives back the original compound, 2, upon re-protonation. Thermal rearrangement of anion 2(-) (Na(+) salt) at 350 degrees C for 2 h produced the isomeric [nido-7,8,10-P(2)CB(8)H(9)](-) (5(-)()) anion, which was isolated as a PPh(4)(+) salt (yield 86%). Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B] COSY, (1)H{(11)B(selective)}, (1)H{(31)P(selective)}, and gradient-enhanced ([(1)H-(13)C] HSQC) magnetic resonance measurements led to complete assignments of all resonances which are in excellent agreement with the structures proposed. Coupling constants, (1)J((31)P,(13)C), (2)J((31)P,C,(1)H), and (1)J((31)P,(31)P), were calculated using the DFT method B3LYP/6-311+G(d,p). The molecular geometries of all compounds were optimized ab initio at a correlated level of theory (RMP2(fc)) using the 6-31G basis set, and their correctness was assessed by comparison of the experimental (11)B and (13)C chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G method. The computations also include the structures and chemical shieldings of the still unknown isomers [nido-7,10,8-P(2)CB(8)H(9)](-) (6(-)) and [nido-7,9,8-P(2)CB(8)H(9)](-) (7(-)).