Aminolysis Of CO₂ Polymers

Carbamate derivatives scaffolds are the important intermediates for synthesizing naturally occurred organic compounds, which have wide applications in pharmaceutical, agrochemical and material terrains. Various catalyst and reaction systems have been developed for the synthesis of carbamates. Nevertheless, the reaction systems usually suffered from rigorous reaction conditions, substrate restriction or/and heavy metal contaminant. Especially, the previous study rarely involved the approach to optically active carbamate derivatives. Herein, we use a series of organic amines as nucleophilic reagents in the ammonolysis of isotactic polycarbonates for highly enantioselective preparation of various optically active carbamate derivatives. The present thesis mainly focuses on the following studies:(1) Aminolysis of optically active polycarbonates with primary or secondary amines as nucleophiles was studied. It was found that the aminolysis did not concern the configuration of chiral carbon in the polycarbonates, and thus provided carbamate with more than 99% enantioselectivity. This method has some advantages, such as atom economy and no heavy metal contaminant. Especially, the aminolysis reaction for the cis-2,3-epoxybutane/CO2 copolymer (PCBC) showed great efficiency without any by-products under mild conditions.(2) The aminolysis mechanism was investigated in detail. For the aminolysis of PCBC, the main pathway involves the unzipping of the copolymer in the backbiting fashion leading to the formation of cyclic carbonate. The resultant cyclic carbonate further reacts with organic amine quickly to give trans-β-hydroxy-carbamates. It was found that the presence of water can promote the ammonolysis reaction.(3) In the process of the aminolysis reactions for PCPC (the CO2/cyclopentene oxide copolymer) and PCHC (the CO2/cyclohexene oxide copolymer), carbonate dimer was detected as intermediate product, which further reacted with amine. The dimer is ascribed to the main reason for diol’s formation. Meanwhile, water can also accelerate the reaction rate.