N-aminopyrroledione-hydrazonoketene-pyrazolium oxide-pyrazolone rearrangements and pyrazolone tautomerism

Flash vacuum thermolysis (FVT) of 1-(dimethylamino)pyrrole-2,3-diones 5 causes extrusion of CO with formation of transient hydrazonoketenes 7. The transient ketenes 7 are observable in the form of weak bands at 2130 (7a) or 2115 cm-1 (7b) in the Ar matrix IR spectra resulting from either FVT or photolysis of either 5 or 1,1-dimethylpyrazolium-5-oxides 8, and these absorptions are in excellent agreement with B3LYP/6-31G* frequency calculations. Under FVT conditions the ketenes 7 cyclize to pyrazolium oxides 8, which undergo 1,4-migration of a methyl group to yield 1,4-dimethyl-3-phenylpyrazole-5(4H)-one 9a and 1,4,4-trimethyl-3- phenylpyrazole-5(4H)-one 9b. All three tautomers of 9a have been characterized, viz. the CH form 9a (most stable form in the gas phase, the solid state and solvents of low polarity), the OH form 9a' (metastable solid at room temperature) and the NH form 9a" (stable in aprotic dipolar solvents). The isomeric 1,4-dimethyl-5-phenylpyrazole-3(2H)- one 12 tautomerizes to the 3-hydroxypyrazole 12'. The crystal structure of the hydrochloride 14 of 9a'/9a" is reported, representing the first structurally characterised example of a protonated 5-hydroxypyrazole.     

Elliptic Systems of PDE with BMO-coefficients

The present paper is concerned with elliptic systems with BMO coefficients: div(Au)=divF, where A(x) is a positive definite matrix whose entries are in BMO and F is a given matrix field in L ^p . We show existence and uniqueness of the distributional solution of class W ^1,p , provided p is close to 2, depending on the BMO norm of A. This result is achieved using a refinement of a classical Theorem of Coifman Rochberg and Weiss about commutators with BMO functions.     

Addition reactions of azoesters with 2-thioquinazolinones

Reaction between diethyl azodicarboxylate (I) and 1,2,3,4-tetrahydro-2-thioquinazolin-4-one (II), as a cyclic model of thiourea, both in alcoholic medium and in inert solvents has been investigated. By carrying out the reaction in an inert solvent, it was possible to isolate an intermediate. Evidence is presented that the intermediate, in turn, was converted into the final products. Structures were unequivocally assigned by mass spectrometry.     

Silylated thiiran-1-oxides: Structure,ring opening and conversion to a benzothiophene.

Silylated thiirans upon oxidation with peroxyacids do not give exclusively the corresponding S-oxides but, in addition some products derived from ring opening. The stereochemistry of the oxidation to thiiran-1-oxides is $\text{anti}$ to the silyl group as demonstrated by X-ray analysis.     

New mesogenic compounds with trans-stilbene oxide as the central chiral core

Several derivatives with the trans-stilbene oxide moiety as the central chiral core were synthesized. With the appropriate substituents, nematic and smectic C phases were observed. One derivative was obtained with an ee of 47 per cent by asymmetric synthesis. The chemical stability of these epoxides is low and they rearrange to give substituted phenyl benzylketones which are also liquid-crystalline. The structure of the two solid phases present in all the derivatives and of the smectic C phases was investigated by X-ray diffraction.     

[4+2]-cycloadditions of thiones with nitrosoalkenes: synthesis of derivatives of 4H-1,5,2-oxathiazine,a new heterocyclic system.

Conjugated nitrosoalkenes, generated $\text{in situ}$$\text{via}$ dehydrobromination of α-bromoketoximes, undergo an easy [4+2]-cycloaddition with thiocarbonyl compounds to give very high yields of the new heterocycles 4H-1,5,2-oxathiazines. The thermolysis and the behaviour to oxidation of these adducts were tested.     

A facile synthesis of substituted benzyl selenocyanates

Benzyl selenocyanates can be made from the corresponding benzylic bromides or chlorides in 30-60 minutes using acetonitrile as a solvent. The products may be obtained pure in satisfactory yields without recourse to chromatography.     

Experimental demonstration of a laterally deformable optical nanoelectromechanical system grating transducer

We experimentally demonstrate operation of a laterally deformable optical nanoelectromechanical system grating transducer. The device is fabricated in amorphous diamond with standard lithographic techniques. For small changes in the spacing of the subwavelength grating elements, lossy propagating resonant modes in the plane of the grating cause a large change in the optical reflection amplitude. An in-plane motion detection sensitivity of 160 fm/square root(Hz) was measured, exceeding that of any other optical microelectromechanical system transducer to our knowledge. Calculations predict that this sensitivity could be improved to better than 40 fm/square root(Hz) in future designs. In addition to having applications in the field of inertial sensors, this device could also be used as an optical modulator.     

Total syntheses of (+)-bernumidine and its unnatural enantiomer

Total syntheses of (+)-bernumidine and its unnatural enantiomer were accomplished through chemoenzymatic dynamic kinetic resolution and ruthenium(II)-catalyzed enantioselective hydrogenation, which provided (R)-salsolidine propyl carbamate and N-acetyl (S)-salsolidine in high yields and enantiomeric excesses, respectively. Both enantiomers of salsolidine were accessed and converted into (+)- and (?)-bernumidine via simple and efficient transformations.