Elimination–addition. Part XII. Rates of addition of amines to alkenyl, allenyl, and alkynyl p-tolyl sulphones

Abstract

Rates of addition of amines to a series of αβ-unsaturated amines have been determined for reactions in ethanol at temperatures between 5 and 45°.

Replacement of a β-hydrogen atom in p-tolyl vinyl sulphone by a methyl group reduces the reactivity of the double bond towards piperidine by a factor of 840. Similar replacement of an α-hydrogen atom reduces the reactivity by a factor of 6500. The operative factors are discussed and the steric contribution towards deactivation by a β-methyl group has been assessed.

Piperidine did not add to isobutenyl p-tolyl sulphone but catalysed its conversion into the methylallyl isomer. The same behaviour was found in reactions with sodium ethoxide, but no reaction occurred with sodium benzenesulphinate. Thiophenoxide gave the normal adduct.

Rates of addition of piperidine to prop-1-ynyl, prop-2-ynyl, and propadienyl p-toly sulphone have been determined. Reaction with the terminal acetylene is preceded by isomerisation to the allene. Such a pathway is excluded for the non-terminal acetylene by the absence of base catalysis, and this sulphone is less than one tenth as reactive as its isomers.