Paolo E. Todesco

Tetrahalogenomethanes: simple reagents for the synthesis of monohalogenated and mixed dihalogenated aromatic heterocycles via metal–halogen exchange from lithium compounds

Abstract Tetrabromo- or tetrachloromethane and 2-lithio derivatives of aromatic heterocycles rapidly produce the corresponding 2-bromo or 2-chloro derivatives in high yields through a metal–halogen exchange mechanism. This kind of reaction was also used to obtain, in good yields, 5-bromo-2-chlorothiazole and 5-bromo-2-chloro-N-methylimidazole.

Contribution to the bromination of conjugate unsaturated ketones: Synthesis of α,β-unsaturated bromo ketones

Abstract Selective bromination of α,β-unsaturated ketones has been achieved by the action of 2,4,4,6-tetrabromocyclohexa-2,5-dienone. The stereochemistry, conformation and relative stability of the bromination products of some steroidic unsaturated ketones have been also determined.

A selective bromination of aromatic amines

A simple method for monobromination of aromatic amines predominantly or exclusively in the para-position is reported. 2,4,4,6-Tetrabromocyclohexa-2,5-dienone is used as the halogenating agent in dichloromethane or chloroform. Protection of the amino-group is not necessary and yields are generally higher than 90%.

Reactions of Hydroxypyridines with 1-Chloro-2,4,6-trinitrobenzene − Product Structure, Kinetics, and Tautomerism

Reactions between 1-chloro-2,4,6-trinitrobenzene and 2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine are reported. 4-Hydroxypyridine produces the product of attack at the nitrogen atom, while 3-hydroxypyridine reacts at the oxygen atom. 2-Hydroxypyridine reacts as an ambidentate nucleophile, providing a mixture of products arising from attack at both the oxygen and the nitrogen atom. Reactions between X-substituted-3-hydroxypyridines (X = H, 5-Cl, 6-CH3) and 1-chloro-2,4,6-trinitrobenzene provided 3-pyridinyl 2,4,6-trinitrophenyl ethers, analysed by 1H and 13C NMR spectra and by X-ray diffraction. Moderate heating of methanolic solutions of 3-pyridinyl 2,4,6-trinitrophenyl ether and of 6-methyl-3-pyridinyl 2,4,6-trinitrophenyl ether caused a methylation reaction of the pyridine nitrogen ring through trinitroanisole, providing 3-hydroxy-1-methylpyridinium picrate and 1,2-dimethyl-5-hydroxypyridinium picrate. Kinetic data are compared and discussed.

Direct monobromination of imidazole and N-methylimidazole

Monobromination of imidazole, N-methylimidazole, and indole is achieved in high yield by treatment with 2,4,4,6-tetrabromocyclohexa-2,5-dienone.

Solvent effect on the ortho : para ratio in the bromination of phenols. Bromination with bromocyclohexadienones and N-bromosuccinimide

Bromination of phenol with N-bromosuccinimide and 2,4,4,6-tetrabromocyclohexa-2,5-dienone has been studied in various solvents. In contrast to bromination with molecular bromine, when these reagents are used the ortho : para ratio is greatly influenced by the solvent and by the concentration of hydrobromic acid concentration present in the reaction medium. The selectivity of these reagents is not due to their ability to furnish very low bromine concentrations, but to their properties as very efficient hydrobromic acid scavengers. The high ortho : para ratios observed during bromination in chlorinated solvents are better explained by an ionic mechanism rather than a radical one involving bromination of the phenoxyl radical.

NEW 2H-1,2,3-DIAZAPHOSPHOLE DERIVATIVES AND RELATED RING-OPENED COMPOUNDS

Abstract The addition of phosphites to the azoalkene 1 gives mixtures of diazaphosphole derivatives 4 and related ring-opened compounds 3 in different proportions depending on the phosphite used. The compounds 3 have the Z-configuration, while cyclic compounds 4 are a mixture of isomers in which predominates the isomer bearing the C4-Ph and OR groups in a trans configuration. When P(OPh)3 is used in dry hexane with rigorous exclusion of moisture the new diazaphosphole derivative 5 is obtained. The results are explained in terms of the relative apicophilicities in the pentacoordinated intermediates.

Synthesis of carbonyl compounds via transamination of Schiff bases

Benzothiazole-2-carbaldehyde or 6-nitrobenzothiazole-2-carbaldehyde can be used for the synthesis of aldehydes or ketones starting from the corresponding amines via transaminations. The method has wide applications and the yields are generally greater than 80%.

Unexpected regioselectivity in the attack of vinyl Grignard reagents to bis(2-benzothiazolyl) ketone

Abstract The addition of vinyl Grignard reagents to bis(2-benzothiazolyl) ketone affords the unexpected O -alkylation products in very high yields.

“Normal” and “cine” substitution in the thioalkoxy-dehalogenation of halogenobenzofuranzans—II: Sensibility of each pathway to the change of alkanethiolate ion

Abstract Thioalkoxy-dehalogenation of 4-halogenobenzofurazans affording “normal” and “cine” substitution products has been more extensively investigated. Evidence for a partial intervention of AEa-type mechanism in NS product formation is now available. The competition of this pathway increases with the bulkiness of thiolate ion. Kinetic data for different thiolates are reported indicating a sensitivity to steric effects not only in the “normal” substitution but also in the “cine” substitution pathway.