Methylenation of optically active γ-polyketones

Abstract

Reaction of poly[(S)-l-oxo-2-methylpropylene] (1) with a dizinc-titanium reagent, CH2(ZnI)2-TiCl3, afforded the corresponding completely methylenated polymer, poly[(S)-l-methylene-2-methylpropylene] (3), in 78% isolated yield. It was confirmed that no significant epimerization took place under the reaction conditions by comparing 13C NMR spectrum of 3 with an atactic analog. Also, poly[(S)-1-oxo-2-butylpropylene] (2) was converted to the methylenated polymer 4. The exo-methylene/ketone ratio of 4 did not exceed 85/15 even by the repeated treatment with CH2(ZnI)2-TiCl3, possibly due to the steric hindrance of side-chain butyl group. In polymer 4, the main chain was suggested to be less flexible based on the smaller peak area and shorter relaxation time (T1) of the main chain protons in 1H NMR.