An accelerated, improved synthetic route for the preparation of polyether-based dendritic fragments

Abstract

An accelerated, improved synthetic strategy for the rapid construction of two different series of polyether-based dendritic fragments is described. Several modifications to the original method for the preparation of these dendritic fragements are detailed. A new branching agent, 5-(3-hydroxypropyloxy)-1,3-resorcinol 4, instead of 5-benzyloxy-1,3-resorcinol 2, is employed in this new synthetic protocol. As a result, the number of synthetic operations in each of the iterative cycle is reduced from three to two, as compared to the original procedure. Each iterative synthetic cycle involves two reactions: a bis- O-alkylation reaction of the brancher 4 with a dendritic bromide [Gn]-O(CH 2) 3Br to give a dendritic alcohol of the next generation [G(n+1)]-O(CH 2) 3OH; followed by a functional group conversion of the dendritic alcohol into the corresponding dendritic bromide [G(n+1)]-O(CH 2) 3Br of the same generation. The reaction yields of each iterative cycle are consistently higher than those of the previously reported three step cycle. Using this new protcol, the preparation of a 5th generation dendritic alcohol 15a could be realized in 10 steps and 23% overall yields from 1,3-dibromopropane.