Methyl 3,4-dihydroxybenzoate

Unfortunately, the presence of the benzylic alcohol moiety at the focal point of the dendrimer, along with the catalyst (used in the urethane formation) led to the formation of undesired side products, presumably due to carbamate interchange. These side reactions were avoided by switching to monomer 19, methyl-3,5-dihydroxybenzoate. While the carbamate linkages of dendrons 53 and 54 were too unstable under the alkylation conditions required to afford larger dendrons, the merits of the concept was adequately demonstrated for this accelerated synthesis of [G-3] dendrons. 

Methyl 3,5-dihydroxybenzoate (25.39 g, 0.151 mol, Aldrich) and potassium carbonate (52.69 g, 0.381 mol) were placed into a 1 L round bottom flask with 200 mL of acetone and a magnetic stirrer. Benzyl bromide (55.04 g, 0.322 mol) was added and washed into the flask with an additional 150 mL of acetone, followed by the addition of a catalytic amount of 18-crown-6 (0.57 g, 2.2 mmol). 

With respect to the oxygenation of methyl 4-hydroxybenzoate (as its tetra-n-butylammonium salt) to methyl 3,5-dihydroxybenzoate, remarkable differences in activity for this test reaction were observed with the three ligand sys-... 

In this new strategy, methyl 3,5-dihydroxybenzoate was subjected to the Gatterman reaction and the resulting product was transformed by chloro-methylation into 90 (Scheme 17), which was found to be different from the phthalide prepared earlier and therefore suggested that the correct structure for the previously prepared phthalide was 89. 

The hyperbranched polymer may contain 3,5-dihydroxybenzoic acid derivatives as the monomer. For example, h5rperbranched polyethylene glycols can be produced by heating methyl 3,5-bis-((8 -hydroxy-3, 6 -dioxaoctyl)oxy)benzoate. This is a hydrolyzate of methyl 3,5-bis((8 -(terf-butyldiphenylsiloxy)-3, 6 -dioxaoctyl)oxy)-benzoate produced from l-bromo-8-(ferf-butyldiphenylsiloxy)-3,6-dioxaoctane and methyl-3,5-dihydroxybenzoate, with dibutyltin diacetate in a nitrogen atmosphere, cf.. Figure 3.21. Thus, a hyperbranched polymer, poly[bis(triethylene glycol)benzoate], is synthesized. 

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