Synthesis of a trimeric lignin model compound composed of α-O-4 and β-O-4 linkages under microwave irradiation

A trimeric lignin model compound composed of alpha-O-4 and beta-O-4 linkages was prepared by the microwave-assisted synthesis, which consisted of three steps: (a) the synthesis of 3-methoxy-4-benzyloxyacetophenone (2) from acetovanillone (1), (b) the bromination of compound 2 to produce 3-methoxy-4-benzyloxy-alpha-bromoacetophenone (3), and (c) followed by a nucleophilic substitution of compound (3) to obtain 3-methoxy-4-benzyloxy-alpha-(3-methoxy-4-(1-propenyl)phenol)-acetophenone (4). The target product was characterized by MS, H-1 NMR and C-13 NMR spectroscopy. It was found that the trimeric compound synthesized can be used as a preferable lignin model compound because it contains guaiacyl structural unit (3-methoxy-4-hydroxy phenyl propane) linked by alpha-O-4 and beta-O-4 linkages. In addition, under the conditions of microwave irradiation, the reaction time of each step is significantly reduced, and the selectivity of target product is greatly improved. The yields of each step and the overall sequence are 95.31%, 87.3%, 90.6% and 75.4% (95.31% x 87.3% x 90.6%), respectively. (C) 2013 Xue-Qing Qiu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.