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

The benzyloxycarbonyl (BOC) group was used for the protection of amino func tions 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 solubili ty of the BOC terminated key intermediates 5 in solvents suitable for conde nsation reactions of oligourethane building blocks in the planned synthesis route prevented the employing of this convenient protective group, the mod ified 3,5-di-tert-butyl substituted BOC (3,5-di-tBBOC) group was found to s ignificantly improve of the solubility of the compounds 16. This allowed th e stepwise building-up of oligourethane model compounds and of telechelic h ard segments precursors 18. Furthermore, due to the better solubility, the 3,5-di-tBBOC protective group also led to considerable improvement of the p urification of intermediate products 13b by liquid chromatography as compar ed to the purification of corresponding BOC terminated compounds 13a.