Umsetzungen von Meldrumsäure mit Isocyanaten und Isothiocyanaten

Summary Meldrum's acid (1) reacts with isothiocyanates and LiH as base, yielding after alkylation the ketene-S,N-acetales3,4 and5. Protonation of the lithium-thiolate2 gives the thioamides7 with tautomers8, which can be methylated with diazomethane to9. From1 and7 it is possible to obtain the amides12.2 reacts with -bromo-carboxylic esters and bromo-acetone, yielding thiazolidones15,16 and thiazolines18.

     

A stereocontrolled route to protected isocyanates from alcohols

Full details are given for a modified Mitsunobu approach to the formation of N-alkylated 1,2,4-dithiazolidine-3,5-diones 2 from a wide range of alcohols 10 with predominantly, inversion of configuration. The resulting products 2 can be regarded as protected isocyanates 6.     

Determination of airborne isocyanates as di-n-butylamine derivatives using liquid chromatography and tandem mass spectrometry

A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]⁺ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.     

Photocycloaddition of Six‐Membered Cyclic Enones to Propen‐2‐yl Isocyanate

On irradiation in the presence of propen‐2‐yl isocyanate ( 4 ), six‐membered cyclic enones 3 are converted into regio‐ and stereoisomeric mixtures of [2+2] cycloadducts 5 – 10 ; the preferentially formed HT products, 5 – 8 , can be converted into the corresponding bicyclic amines by acid hydrolysis, whereas, under these conditions, the regioisomeric HH‐isocyanato derivatives undergo a retro‐Mannich reaction.     

An Hptlc Approach to Quantitative Determination of Some Prostaglandins in Serum: Study in Normal and Asthmatic Subjects

Abstract

A modified HPTLC technique was applied in investigating venous peripheral blood concentrations of PGE1, FGE2, FGF1α, FGF2α, PGA1 and PGAP2 in three subjects with occupational asthma, undergoing specific bronchial challenge test with chemical sensitizers, as well as in two control subjects, exposed to the same test. The findings obtained show that the technique employed in our study is quite suitable and could be Useful to acquire more information on some biochemical events occurring during asthmatic responses to bronchial challenge.     

One-pot synthesis of selenocarbamates from isocyanates and diselenides using the Zn/AlCl3 system

Several N-alkyl/aryl-Se-alkyl/(aryl)selenocarbamates were prepared from various isocyanates and diselenides by reductive cleavage of Se-Se bond with the Zn/AlCl3 system in dry acetonitrile at 80℃.     

A Novel and Efficient Synthesis of 2,3-Dichloroquinoline

2,3-Dichloroquinoline was prepared in three steps in good overall yield from commercial 3-bromoquinoline via N-oxide formation and rearrangement to 3-bromocarbostyril, followed by a one-pot conversion to 3-bromo-2-chloroquinoline and halogen exchange to the title compound.     

Functionalisation of mesoporous silica nanoparticles with 3-isocynatopropyltrichlorosilane

The functionalisation of Mesoporous Silica Nanoparticles (MSN) with the isocyanate group was carried out. The excellent reactivity of 3-isocynanatopropyltrichlorosilane allowed its grafting on the surface of MSN in mild conditions. Further reaction with different nucleophiles bearing primary amino groups led to the formation of a urea linkage and thus the covalent grafting of the nucleophiles to the MSN surface.     

Highly stereoselective De-Novo synthesis of protected 2-amino-3-C-methyl-2,3-dideoxy-d-altrose

A new strategy for the stereoselective synthesis of 2-amino-2-deoxy-aldoses is described. Therefore epoxy carbamates are reacted with isocyanates to furnish urethanes, which will form the title compounds with high diastereoselectivities under basic conditions and O,O-migration of the carbamoyl group.     

New synthesis of polyfluoroalkanesulfonylureas

This study describes a new synthesis of F-alkanesulfonyl ureas by reaction of the sodium salt of perfluoroalkane sulfonamide (R_F = C₄F₉, C₆F₁₃) with some isocyanates in anhydrous THF. The perfluorinated sulfonylureas are obtained, in one step, from moderate to good yields.