Asymmetric Polymerization and Oligomerization of 3-Phenylpropanal with Grignard Reagent−(−)-Sparteine Complexes with Termination by Tishchenko Reaction

Abstract

3-Phenylpropanal (3-PPA) was polymerized with Grignard reagent−(−)-sparteine complexes, such as ethylmagnesium bromide−(−)-sparteine (EtMgBr−Sp) and n-octylmagnesium bromide−(−)-sparteine (OctMgBr-SP) complexes, in toluene at low temperature. The poly(3-PPA) obtained showed optical activity with negative rotation ([α]25365 −33° to −56°), which may be based on a predominant one-handed helical conformation of the main chain, and also exhibited a signal due to an ester carbonyl group at 1738 cm-1 in its IR spectrum. This means that the polymer has an ester group at the ω-end which is formed by a Tishchenko-type termination reaction between the growing chain end and the 3-PPA monomer. The poly(3-PPA) is stable at room temperature, whereas the poly(3-PPA) obtained with EtMgBr alone at −78 °C degrades slowly even in the solid state to 3-PPA monomer at room temperature. 1H and 13C NMR spectra of the poly(3-PPA) showed rather sharp resonances, suggesting that the polymer may be stereoregular, although the tactici...