Highly efficient synthesis of 2-mercaptobenzothiazole derivatives in water: metal sulfide–disulfide dynamic interchange reaction

A convenient and efficient method for the synthesis of 2-mercaptobenzothiazoles from disulfide and CS2 was performed by dynamic interchange reaction between a disulfide and a metal sulfide in water.

Unusual traits of cis and trans-2,3-dibromo-1,1-dimethylindane on the way from 1,1-dimethylindene to 2-bromo-, 3-bromo-, and 2,3-dibromo-1,1-dimethylindene

Do not rely on the widely accepted rule that vicinal, sp3-positioned protons in cyclopentene moieties should always have more positive 3 J NMR coupling constants for the cis than for the trans arrangement: Unrecognized exceptions might misguide one to wrong stereochemical assignments and thence to erroneous mechanistic conclusions. We show here that two structurally innocent-looking 2,3-dibromo-1,1-dimethylindanes violate the rule by means of their values of 3 J(cis) = 6.1 Hz and 3 J(trans) = 8.4 Hz. The stereoselective formation of the trans diastereomer from 1,1-dimethylindene was improved with the tribromide anion (Br3 −) as the brominating agent in place of elemental bromine; the ensuing, regiospecific HBr elimination afforded 3-bromo-1,1-dimethylindene. The addition of elemental bromine to the latter compound, followed by thermal HBr elimination, furnished 2,3-dibromo-1,1-dimethylindene, whose Br/Li interchange reaction, precipitation, and subsequent protolysis yielded only 2-bromo-1,1-dimethylindene.

A computational study of the threshold energies of the 1,2-FCl interchange reaction of chlorofluoroethanes

The 1,2-FCl rearrangement reaction of a series of haloethanes is investigated by comparisons of the optimized ground- and transition-state geometries. Investigation of the effect of level of theory and basis set shows that the trends in threshold energies for rearrangement are reproduced across all levels of theory and basis set, and hence that a moderate level of theory and basis set is adequate for investigating the important trends in this reaction. Threshold barriers increase when a large number of fluorine atoms are attached to the carbon atom bearing the interchanging fluorine, suggesting that the C–F bonds prove difficult to distort to the transition geometry; the increase is smaller for fluorine substitution on the carbon atom bearing the interchanging hydrogen atom. By considering sets of isomeric reactions, the barrier height is shown to closely follow the thermodynamic stability of the alkane undergoing rearrangement; however there is a secondary effect owing to the relative stability of the transition geometry. This relative stability can be related to the thermodynamic stability of a series of isomeric alkenes that resemble the transition geometry without the rearranging atoms. This series of molecules constitute an unusual set owing to the ability to consider these three contributions to the activation barrier separately.