Zdenek Janousek

Alpha-cyclization of Tertiary-amines .3. Captodative Or Push-pull Enamines Form Pyrrolines, Pyrrolizidines and Their Ring Homologs With Dimethyl Acetylenedicarboxylate in a Highly Diastereoselective Reaction

The title one-pot reaction occurs through a sequence of [2+2] cycloaddition ring opening to dienamines and formation of a 1,5-dipole by [1,6] hydrogen-shift. This intermediate may cyclize or in sterically suitable cases and at lower temperatures, lead to isolable N-vinyl enamines by proton transfer.

Captodative Substituent Effects .31. Olefins With Captodative Substitution in [2+2] Cyclo-additions

Abstract Olefins with captodative substitution are excellent partners in [2+2] cycloadditions leading to cyclobutane derivatives. The reaction rates increase with the radical stabilising power of the substituents. Thio- and selenoalkyl(aryl) substituted gemdifluoroolefins allow the synthesis of new cyclobutane derivatives.

Trifluoromethylated Heterocycles From Beta-trifluoroacetyl-lactams and Beta-trifluorobenzolactams

Trifluoromethyl substituted heterocycles have been prepared by condensation of the new beta-trifluoroacetyl-lactams 1 and -benzolactams 2 with methylhydrazine and benzamidine as bis-nucleophiles without opening of the lactam structure.

Catalytic, enantioselective, inverse electron-demand Diels-Alder reactions of 2-pyrone derivatives

The lanthanide-catalysed, diastereo- and enantio-controlled Inverse Electron-Demand Diels-Alder cycloadditions of 3-carbomethoxy-2-pyrone derivatives with electron-rich dienophiles is shown to proceed with high levels of asymmetric induction.

Captodative substituent effects XXI. : Synthesis of selenenylated captodative olefins via selenenyl halide addition to olefins bearing electron-withdrawing substituents

Abstract Addition of methane- and benzeneselenenyl bromide or chloride and benzene sulfenyl chloride to carbon-carbon double bonds substituted by electronwithdrawing groups is achieved in solvents of different polarity. Two regioisomeric adducts 6 and 7 or 8 and 9 are generally formed, which can be interconverted by equilibration in refluxing acetonitrile. It is of mechanistic interest that the regioisomers may also derive from selenenyltrihalide adducts. In comparison to acrylic esters, the propiolic ester reacts more slowly, producing mainly the α-selenenyl adduct. Dehydrohalogenation of adducts provides a general and valuable method for the preparation of olefins carrying methyl or phenylselenenyl groups in α-position to electron-withdrawing substituents.

Cumulogy Supported By X-ray-analysis of 1,1-bis(dimethylamino)-4,4-dicyanobutatriene

The new title compound 7 and its corresponding diene 4 are the cumulogue and vinylogue of known 1,1-bis N,N-dimethylaminomethylenemalononitrile 8, respectively. These compounds 4 and 7 are crystalline with dipolar character and show exceptionally short central bonds.

Novel thermal tetracyclization by intramolecular azine criss-cross addition

An easy, thermally initiated reaction of homoallenylazine 1 affords the new fused heterocyclic system 2 consisting of four five-membered rings in ten-membered carbocycle around the hydrazine moiety.

2-Phenylthio-3,3,3-trifluoropropene, its sulfoxide and sulfone: Synthesis and reactivity in 1,3-dipolar cycloadditions.

Derivatives of 3,3,3-trifluoropropene 1 : alpha-sulfide 2, sulfoxide 3, sulfone 4 and bromide 6 are useful trifluoromethylated synthons. On reaction with diazo compounds, these derivatives can afford trifluoromethyl substituted pyrazolines, pyrazoles, cyclopropanes or allylsulfones in fair to excellent yields. 1,3-Dipolar cycloaddition of trifluoropropene derivatives 2-4 with N-benzylazomethine ylide provides disubstituted 3-trifluoromethyl-pyrrolidines.

Trifluoromethylated Pyrimidines Starting From Beta-trifluoroacetyl-lactams, Beta-trifluoroacetyl-lactone and Beta-trifluoroacetyl-cyclanone

A synthesis of trifluoromethylated pyrimidines from beta-trifluoroacetyl-lactams and -benzolactams is accomplished by reaction with benzamidine as bis-nucleophile. This condensation is also extended to cyclic trifluoromethylated 1,3-diketones and 3-aroyl-2-pyrrolidinones.

Capto-dative substituent effects—VIII

Abstract Dehydrodimerization is suppressed completely in the presence of radicophiles such as cd-substituted olefins. Particularly α-t-butylmercaptoacrylonitrile (TBMA) has been examined as a trapping agent for carbon centered radicals. The adducts dimerize thus building C4-bridges between the original radicals. This general principle is synthetically useful as demonstrated by C4-bridging of alkanes, ethers, amines, amides, aldehydes and ketones.