Protonation and alkylation of 1-arylpropenyl-lithium

Abstract

The protonation and alkylation of 1-arylpropenyl-lithium (1a–c) in ether was undertaken systematically; the regio- and stereo-chemistry being influenced by various factors. The characteristic features are as follows. (a) Protonation occurs predominantly at C-3, whereas the sterically more crowded C-1 is the more favoured site for alkylation, and (b) although 1-arylpropenyl-lithium (1) seems to exist mainly as the E-isomer, in some cases the product (3) or (5) having the Z-configuration is produced from attack at C-3 in a significant amount together with the E-isomer, e.g. protonation by oxygen acids in the presence or absence of tetramethylethylenediamine and methylation of the p-methoxy derivative (1a).