F.J.J. de Kanter

Preorganized frustrated Lewis pairs.

Geminal frustrated Lewis pairs (FLPs) are expected to exhibit increased reactivity when the donor and acceptor sites are perfectly aligned. This is shown for reactions of the nonfluorinated FLP tBu(2)PCH(2)BPh(2) with H(2), CO(2), and isocyanates and supported computationally.

A novel three-component reaction toward dihydrooxazolopyridines.

Isocyano dihydropyridones accessible via a recently reported multicomponent reaction react with aldehydes and amines to afford dihydrooxazolopyridines in high yield. The scope and limitations of this novel multicomponent reaction were investigated. The efficient combination of two highly variable multicomponent reactions allows the construction of a very broad range of dihydrooxazolopyridines, an unexplored class of bicyclic compounds. The implications of the observed reactivity profile for the mechanism of this multicomponent reaction are discussed.

Efficient library synthesis of imidazoles using a multicomponent reaction and microwave irradiation.

Optimization of Radziszewskis four-component reaction employing a microwave-assisted protocol, led to a small library of 48 imidazoles with a success rate of 65% (conversion > 45%). All three diversity points of the four-component reaction were varied. Aromatic and aliphatic inputs were successfully implemented and mono-, di-, tri- and tetrasubstituted imidazoles with various substitution patterns were synthesized. Furthermore, unsymmetrical diketones could successfully be used which improved the intrinsic diversity of the method significantly. If the unsymmetrical diketone 1,2-phenylpropanedione (R1 and R2) was used two regioisomers were formed. Depending on the type of amine (R4) and aldehyde (R3) applied, regioselectivity was modest to good. Based on these results, a reaction mechanism is proposed.

IN SEARCH OF STABLE LITHIUM PENTAORGANYLSILICATES; SPECIAL ROLE OF FIVE PHENYL LIGANDS AND OF LIGANDS CONTAINING THE 1,4-(1,3-BUTADIENEDIYL) UNIT

Abstract Among several tetraorganylsilanes tested, only 4–6, containing the 1,4-(1,3-butadienediyl) unit, have been found to form, by addition of a σ-organolithium, lithium pentaorganylsilicates identifiable by characteristic 29Si-NMR chemical shifts. Lithium silicates formed from 4 are of particular stability (and correspondingly low reactivity) and appear to have trigonal-bipyramidal structures that undergo stereomutation with ΔH≠ ca. 50 kJ/mol, ΔS≠ ca. −20 J/kmol. So far, lithium pentaphenylsilicate (3) is the only other lithium pentaorganylsilicate that could be identified by 29Si-NMR.

1,5-annelated 4-methylenecyclopentenes by intramolecular type I zinc-ene reactions followed by Pd(0)-catalyzed cyclization

3-(Alk-m-ynyl)-2-(methoxymethyl)-2-propenylzinc bromides 1 (m = 4,5,6) undergo intramolecular carbometallation. The products 2 were converted by Pd(0)-catalyzed cyclization to 1,5-annelated 4-methylenecyclopentenes 3.

Generation of molecular diversity using a complexity-generating MCR-platform towards triazinane diones†

Triazinane diones, readily generated by a recently reported multicomponent reaction, can be easily alkylated with various alkyl halides, allowing a wide variety of complexity-generating secondary reactions. Because of the high variability of the initial multicomponent reactions and the multiple possibilities for participation of substituents in the secondary reactions, a highly diverse set of complex products was obtained in short and efficient reaction sequences.

Chemical shielding anisotropy of 13C in CH3 CN determined by NMR spectroscopy of the dielectrically oriented molecule

A successful determination of a shielding anisotropy with electric field NMR is reported for the first time. The nucleus studied is the nitrile 13C in liquid acetonitrile. From 13C frequency changes and 14N quadrupolar splittings upon dielectrical alignment, the chemical shift anisotropy of 13C is found to be 378 ± 20 ppm. The 14N quadrupole coupling constant is obtained from 1H and 14N spectra of the orientated molecule, giving a value of 3·47 ± 0·16 MHz.

Addition of 2-(phenoxymethyl)-2-propenylmagnesium chloride to epoxides followed by Pd(0)-catalyzed cyclization: a one-pot synthesis of 3-methylenetetrahydropyrans

Abstract Addition of 2-(phenoxymethyl)-2-propenylmagnesium chloride to epoxides afforded the ring opening products 3 which were converted by Pd(0) to 3-methylenetetrahydropyrans 4 .

X-ray crystal structure and hydrocarbon solution behaviour of tetrameric 2,2-Bis(methoxymethyl)-1-propyllithium

Abstract The title compound is a tetramer in the solid state and in hydrocarbon solution.