Alexander J. Lawson

On the structure of acylaminyl radicals

Bei der Pyrolyse der Hydroxylamin-Derivate (I) bzw. (VI) werden die Radikale (II) und (III) bzw. (VII) und (II) erhalten, aus denen die Folgeprodukte (IV) und (V) bzw. (VIII) entstehen.

Oxaziridinyl free radicals

The e.s.r. solution spectra of two 3,3-disub-stituted oxaziridinyl free radicals are reported, and the isolation of a 2H-oxaziridine is described.

Thermal rearrangement of O-methyleneamino thiocarbamates

The rate of the thermal, uncatalysed, [1,3] rearrangement of aromatic O-methyleneamino thiocarbamates to S-methyleneamino thiocarbamates in solution is insensitive to changes in both solvent polarity and substituent on ring and imino-carbon atoms, suggesting a transition state involving little charge separation. The occurrence of rearrangement via a radical pair is suggested by the detection by e.s.r. spectroscopy of aromatic iminyls, generated as transients during rearrangement.

Thermal rearrangement of O-thiocarbamoylated hydroxamic acids: a 1,3 radical shift

The rearrangement of N-aroyl-N-methyl-O-(NN-dimethylthiocarbamoyl)hydroxylamines (II) probably proceeds by a radical cage mechanism as shown by kinetic measurements and CIDNP effects in the n.m.r. spectra of the products.

Hetero-cope rearrangement via an isolable intermediate

The [3,3] rearrangement (1)–(3) takes place in methanol solution via the isolable intermediate (2).

Reaction of 4-arylmethylene-3-phenylisoxazolones and 4-arylmethylene-1,3-diphenylpyrazolones with enamines and nucleophilic heterocycles

4-Arylmethylene-3-phenylisoxazolones (1) and 4-arylmethylene-1,3-diphenylpyrazolones (2) were treated with enamines (8), 3-phenylisoxazol-5(4H)-one (4), 1,3-diphenylpyrazol-5(4H)-one (6), and 2-phenyloxazol-5(4H)-one (3). The enamines were β-alkylated to give 1:1 adducts (9) and (10). The reaction of (1) with (6) and (2) with (4) gave symmetrical benzylidenedi-isoxazolones and -pyrazolones (7). 2-Phenyloxazol-5(4H)-one with (1) gave 4-benzylidene-2-phenyloxazolone (5) by transfer of the benzylidene group and with (2), a 1:1 adduct (19) isolated as the corresponding ethyl hippurate derivative (20).

Conformation and stability of 1,1-diphenylmethyleneiminyl

The magnitudes of ring-proton coupling in the title radical are consistent with those calculated for the conformation (III) which is also estimated to be the most stable rotamer.

On anchimerically assisted homolysis via sulphide functions

In contrast to O–O fission, anchimeric assistance from sulphide functions in the rate of unimolecular fission of the N–O bond is only marked for heterolysis reactions; analogous homolyses are very much less accelerated, although bridged radical intermediates are involved.

Mechanism of the thermal rearrangement of N-aroyl-O-(NN-dimethylthiocarbamoyl)-N-methylhydroxylamines

Mechanistic investigations on the thermolysis of N-aroyl-O-(NN-dimethylthiocarbamoyl)-N-methylhydroxylamines lead to the conclusion that the thiono–thiolo rearrangement proceeds, at least in part, by a radical cage process. This is accompanied by a reaction, due to escaped amidyl radicals, leading to the corresponding amide in a hydrogen abstraction process. The proposed mechanisms are supported by CIDNP effects, kinetic studies with diphenyl-picrylhydrazyl, and measurement of the activation parameters of the observed unimolecular reaction.

Thermal 1,3-rearrangement of N-benzoyl-N-methyl-O-thiocarbamoyl-hydroxylamines (thiocarbamoyl N-methylbenzohydroxamates)

The preparation and thermal rearrangement of several of the title compounds are described. S-Carbamoyl N-methylbenzothiohydroxamates and the corresponding N-methylbenzamide are the principle products. The rate coefficients for rearrangement change only slightly with variations in the aromatic substituent or solvent polarity, suggesting either a concerted or a free radical pair pathway, rather than mechanisms with a polar or an ionic transition state.