Cornelius J. Meyer

Iminyls. Part 1. Generation of iminyls

Four methods for producing iminyl radicals are described: oxidation of imino-oxyacetic acids with persulphate, thermolysis of the corresponding peresters, oxidation of oxime ethers with di-t-butyl peroxide, and photolysis of oxime oxalates. The first two are the most useful for chemical studies.

Phosphonium ylide-catalyzed cyclotrimerization of ethyl propynoate

ABSTRACT The cyclotrimerization of ethyl propynoate (2) to yield aromatic triesters is shown to proceed via consecutive [2 + 2] cycloadditions of ethoxycarbonylmethylenetriphenylphosphonium ylide (1) to three moles of (2), followed by cyclization and elimination of (1).

General synthesis of symmetrical and unsymmetrical organic sulphides under non-basic reaction conditions

General syntheses of a variety of unsymmetrical methyl and ethyl sulphides, by treatment of the appropriate organic halides or the corresponding sulphonium salts with an excess of dimethyl or diethyl sulphide, are described. When organic halides are treated with the corresponding unsymmetrical methyl sulphides, symmetrical sulphides are produced via demethylation of the intermediate methylsulphonium salts by the halide ions.

Iminyls. Part 6. Diazo- and alkoxy-iminyls

Several diazo- and one alkoxy-aryliminyl(s) have been generated. These (i) fragment to arenecarbonitrile and aryl or alkoxyl radical, respectively, and (ii) abstract hydrogen to give the corresponding imines. The imines derived from the diazoiminyls react further to give triazoles and 2-aroylaminoazoarenes in low yield. Fragmentation of the phenyldiazoiminyls occurs more readily than that of the benzyloxyiminyl and the effect of α-substituents (phenyldiazo, benzyloxy, alkyl) on the ease of fragmentation of phenyliminyls is discussed.

Stereospecific formation of a vinyl sulphide via a sulphonium ylide–salt coupling reaction

The identification of tetramethyl 1 -(methylthio)hexa-1,5-diene-2,3,4,5-tetracarboxylate (X), formed in low yield during attempted oxidation of dimethyl α-(bromomethyl)fumarate (IV) by dimethyl sulphoxide in the presence of a weak base, is described. It is shown that the production of the vinyl sulphide (X) under these conditions takes place via the intermediate (2,3-bismethoxycarbonylprop-2-enyl)dimethylsulphonium bromide (XIV), which undergoes a stereospecific Michael addition reaction with the derived sulphonium ylide (XX).

Functional group analysis

Initial questions where all results and observations of the chemical tests relating to the selected functional groups are systematically tabulated help to develop a methodical approach to analyzing problems. The tabulated comparisons can facilitate the students approach to the classical questions, preventing random attempts with no regard for a process of elimination (if applicable).

Conservation of the chair-like transition state by base-catalysed epimerization of meso-tetramethyl hexa-1,5-diene-2,3,4,5-tetracarboxylate prior to its Cope rearrangement

meso-Tetramethyl hexa-1,5-diene-2,3,4,5-tetracarboxylate (5) rearranges at 20–50 °C in the presence of sodium carbonate to (E,E)-tetramethyl hexa-1,5-diene-1,2,5,6-tetracarboxylate (7), by base-catalysed epimerization followed by Cope rearrangement of the resulting (±)-tetraester (6)via the expected four-centred, chair-like transition state. In the absence of base the meso-tetraester (5) undergoes [3,3] sigmatropic rearrangement to produce (E,Z)-tetramethyl hexa-1,5-diene-1,2,5,6-tetracarboxylate (8) exclusively.

Formation of vinyl sulphides via successive sigmatropic rearrangements of an allylic sulphonium ylide

It is shown that the sulphonium ylide (VIII) derived from the bisallylic sulphonium salt bis-(2,3-dimethoxycarbonylprop-2-enyl)methylsulphonium tetrafluoroborate (VII) undergoes a [2,3] sigmatropic rearrangement to produce the diastereoisomers (IX) and (X) of tetramethyl 3-(methylthio)hexa-1,5-diene-1,2,4,5-tetracarboxylate. The stereochemical outcome of the Cope rearrangements of the sulphides (IX) and (X) to (E,E)- and (Z,E)-tetramethyl 6-(methylthio)hexa-1,5-diene-1,2,4,5-tetracarboxylate (XI) and (XII), respectively, is invoked to determine the relative configurations at the chiral centres of (IX) and (X).