Synthesis and application of 3,5-Di-tert-butylbenzyl chloroformate for the protection of amino functions and the improvement of solubility in polyurethane synthesis

Abstract

The benzyloxycarbonyl (BOC) group was used for the protection of amino functions in the stepwise synthesis of molecularly uniform oligourethanes based on 1,5-naphthalene diamine (NDA) as well as polyurethane (PUR) elastomers with molecularly uniform NDA-based hard segments. Whereas the poor solubility of the BOC terminated key intermediates 5 in solvents suitable for condensation reactions of oligourethane building blocks in the planned synthesis route prevented the employing of this convenient protective group, the modified 3,5-di-tert-butyl substituted BOC (3,5-di-tBBOC) group was found to significantly improve of the solubility of the compounds 16. This allowed the stepwise building-up of oligourethane model compounds and of tele-chelic hard segments precursors 18. Furthermore, due to the better solubility, the 3,5-di-tBBOC protective group also led to considerable improvement of the purification of intermediate products 13b by liquid chromatography as compared to the purification of corresponding BOC terminated compounds 13a