Roger H. Smithers

Reactions of a mono- and a tri-substituted epoxide with some simple and β-substituted primary amines; novel examples of electrophilic anchimeric assistance

The reactions of a number of primary amines with a mono- and a tri-substituted epoxide have been examined. The results indicate that the presence of water has a strong reaction-accelerating effect for both heterocycles, and product studies have led to the isolation of secondary and tertiary amino-alcohols. Reactions of some amines possessing a weakly acidic group in the β-position proceeded anomalously rapidly, even under dry conditions, and it is suggested that these represent new examples of electrophilic anchimeric assistance.

Effect of a β-silyl group on the regiochemistry of enolisation of ketones

1-Dimethyl(phenyl)silylpentan-3-one(4),3-dimethyl(phenyl)silylcyclopentanone(10) and 3-dimethyl (phenyl)silylcyclohexanone (16) are deprotonated by lithium di-isopropylamide in favour of enolate formation away from the silyl group to the extent of 70 : 30, 70 : 30, and > 95 : 5, respectively. The effect of the silyl group appears to be largely steric in origin.

A One Pot E-Selective Route to Unsaturated Esters Using Lithium Methoxyacetylide from A Non-Acetylenic Precursor

Abstract Lithium methoxyacetylide generated from a stable perhalogenated vinyl ether precursor was reacted with a number of carbonyl compounds and the derived acetylenic carbinols rearranged to yield α, β-Unsaturated Esters in a one pot reaction. The process is E-Selective.

External activation of epoxides by polarising groups borne by the nucleophile

There is much current interest in the chemistry of epoxides which are activated as electrophiles, but almost without exception, systems studied thus far involve internal activation by hydroxy-groups. Herein a new mode of external activation is pointed out, whereby increased susceptibility to nucleophilic attack occurs by interaction of the epoxide with polarising groups such as OH and SH borne by primary amine nucleophiles. Rate data for the reactions of a number of 2-substituted ethylamines with methyloxiran in tetrahydrofuran, ethanol, and water show that while a 2-mercapto-group may increase rates 10–25 fold, a 2-hydroxy-group only appears to be effective in aprotic solvents. Determined values of ΔH‡ and ΔS‡ are discussed, and interpreted as providing evidence for the operation of an intramolecular concerted-like activation process. In drawing a biological analogy, particularly with regard to the physiological action of toxic epoxides, these results draw attention to the possible need to consider alternative modes of in vitro action.