Multiple bond migration with participation of a protophilic agent 5. Double bond migration in heteroallylic systems

The pathways of migration of the double bond in heteroallylic systems XCH2C H=CH2 (X = NMe2, OMe, PMe2, and SMe) with participation of hydroxide ion we re investigated by the ab initio RHF/6-31+G* and MP2/6-31+G* methods. The r esults are compared with those of analogous calculations of the systems wit h X = H, Me. Conformational isomerism of the initial molecules and reaction products, as well as the structure of intermediate carbanions, are conside red. Increased acidity of compounds containing atoms of the third-row eleme nts is explained in terms of a negative hyperconjugation model. I,3-Hydroge n shift with participation of hydroxide ion in the systems XCH2CH=CH2 resul ts in double bond migration toward substituent X to form 1-hetero-1-propene s XCH=CHMe. Comparison of the energies of the final products indicates ther modynamic preferableness of the formation of E-isomers. At the same time, i n the case of substituents with atoms of the second-row elements the intera ction of sigma-bonds of the substituents and the p-AO of the terminal C ato m additionally stabilizes Z-isomers of the carbanions and can be the reason for preferable kinetically controlled formation of these isomers. If the s ubstituents contain atoms of the third-row elements, the formation of E-iso mers of 1-hetero-1-propenes becomes both kinetically and thermodynamically predominant.