(4+2)-cycloaddition of nitroalkenes with ynamines; formation of a 4H-1,2-oxazine 2-oxide derivative

The formation of a thermally unstable (4+2)-cycloadduct, a 4H-1,2-oxazine 2-oxide derivative ( ), from the reaction of 1-nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene has been proven by the structure elucidation of isoxazole derivative which results from thermal rearrangement and by the structure determination of the 1,3-dipolar adducts of with electron-deficient acetylenes

Chemistry of pyrrolizines; reactions with cyanogen bromide and trifluoroacetic anhydride

Interaction of the pyrrolizine 3 with cyanogen bromide in a tetrahydrofuran/water mixture affords addition to the enamine double bond with formation of 5 which can be aromatized to 6 by silica gel. Reaction of 6 with cyanogen bromide in the same solvent mixture yields the indoline 8a which structure is proved in a chemical way by conversion of the product into the aldehyde 8d. The different reaction pathway is discussed in terms of steric hindrance by the ester groups. Treatment of 6 with trifluoroacetic anhydride gives the trifluoroacetylated compound 11. Removal of the sterically hindered ester groups in 6, with acetic acid in quinoline at 200°, is accompanied by the simultaneous decarboxylation to yield the pyrrolo[1,2-a]indole 1

The stabilization of thiepin by substitution

Resonance energies of 430 substituted thiepins have been calculated using a simple Hückel method described before. The results predict that thiepins substituted with electron-withdrawing groups (methoxycarbonyl and fluorine) will be less antiaromatic than the parent thiepin. Thus the calculated REPE of the only known type of monocyclic thiepin viz. 3,4 - bis(methoxycarbonyl) - 5 pyrrolidinothiepin (-0.007β) is less negative than that of the parent thiepin

Novel applications of the “t-amino effect” in heterocyclic chemistry; synthesis of 5H-pyrrolo- and 1H,6H-pyrido[1,2-a][3,1]benzoxazines

Trifluoroacetylated N,N-dialkylanilines react in refluxing 1-butanol to benzoxazine derivatives via an intramolecular] [1, 5] hydrogen shift and subsequent cyclization of the dipolar intermediate

A nesting conformation of the 5′-bromo-1′,3′-xylyl-18-crown-5·tert-butylammonium hexafluorophosphate complex; the correlation of the structures of crown ether complexes in the solid state and in solution

Single-crystal X-ray analysis of the 5′-bromo-1′,3′-xylyl-18-crown-5· tert-butylammonium hexafluorophosphate complex shows that the complex is of the “nesting” type in which the cation and the aryl group are on the same face of the macroring and that the macroring has a (ag+a) (ag−a) (ag+a) (ag−a)(ag+a) (ag−a) conformation

Novel applications of the "t-amino effect" in heterocyclic chemistry. Synthesis of a pyrrolo[1,2-a]quinazoline and 5H-pyrrolo[1,2-a][3,1]benzothiazines

1-(1-Pyrrolidinyl)benzenes substituted with an imino- or an in situ generated thiocarbonyl group in the 2-position rearrange upon heating to quinazoline and benzothiazine derivatives, respectively

On the mechanism of the reaction of enamines and dimethyl acetylenedicarboxylate (DMAD) in polar and apolar solvents

[2+2]-Cycloadducts of enamines and DMAD, formed in apolar solvents, isomerize to pyrrolizine derivatives under mild conditions in protic polar solvents like methanol and 1-butanol

The madelung synthesis of dihydro-1H-pyrrolo- and tetrahydropyrido[1,2-a]- indoles under mild conditions

Benzeneacetonitriles substituted with lactam moieties in the ortho-position cyclize under the influence of a base, dependent on the ring-size of the lactam function, to dihydropyrrolo-, tetrahydropyrido[1,2-a]indole or dihydro-1-benzazepin derivatives, respectively

Nitrate And Bicarbonate Selective Chemfets

The development of durable anion selective CHEMFET micro sensors is described. Selectivity in these sensors is either obtained from differences in hydration energy of the anions (the Hlofmeister series, giving nitrate selectivity) or by introduction of a new class of uranyl salophene ionophores (bicarbonate selectivity). The durability of the nitrate sensor was enhanced by using polysiloxane membranes in which 1 cationic tetraalkylammonium sites were covalently bound to the membrane matrix

Solid-liquid (S-L) an liquid (L-L) phase transfer of salts via ‘encapsulated’ crown ether cation complexes

In recent years crown ethers have been successfully used for the transport of salts, both inorganic and organic, from an aqueous phase to organic solvents. Our work has extended the applicability of these crown ethers to the transport of salts from the solid state into solution both aqueous and nonaqueous. For this purpose a number of novel crown ethers have been synthesized that have in addition to a polar ‘cavity’ formed by donor atoms of the macrocyclic ring, (an) additional anionic functional group(s) covalently bound to the macroring.\ud \ud The first part of the lecture will deal with the design of such macrocycles that can encapsulate a spherical cation in a flexible cavity or that can encapsulate non-spherical cations. e.g. uronium cations, in a relatively rigid cavity.\ud \ud Together with the synthesis results of complexation studies using 1H NMR spectroscopy will be discussed.\ud \ud In the second part the use of crown ethers for the transport of sparingly soluble salts from the solid state into aqueous solutions will be dealt with. The emphasis will be placed on theoretical models that can be used to described such phase transfer processes and to predict thermodynamic stability constants of complexes required for solubilisation.\ud \ud The lecture will conclude with a comparison of these models with experimental results