Okay so I was hoping you'd say a C-C coupling. The first thing is id take vanillic acid and iodinate or brominate it. Heres a procedure for iodination:
A mixed solution of 0.345 g (2.1 mmol) of 4-hydroxy-3-methoxybenzoic acid, 0.27 g (1.05 mmol) of molecular iodine and 0.45 g (5.7 mmol) of pyridine was stirred at 40.deg.C, and 0.26 g (2.31 mmol as hydrogen peroxide) of a 30percent aqueous hydrogen peroxide solution was dropped thereto over 0.4 hour. After the completion of addition of the aqueous hydrogen peroxide, the reaction solution was maintained at 40.deg.C, and stirred for 1.6 hours. The total reaction time was 2 hours. Then, 1.0 g of a 20percent aqueous sodium sulfite solution was added thereto. At room temperature, the reaction solution was added little by little to 4 g of a 2N aqueous hydrochloric acid solution under stirring. After the whole amount of the reaction solution was added thereto, 15 g of water was added thereto. The precipitated crystals were separated by filtration and vacuum dried at 70.deg.C to obtain 0.525 g of crystals. According to analyses of the crystals and the mother liquid with high performance liquid chromatography, conversion of 4-hydroxy-3-methoxybenzoic acid was 100percent, selectivity of 4-hydroxy-3-methoxy-5-iodobenzoic acid was 93percent on both substrate basis and iodine basis, isolated yield of 4-hydroxy-3-methoxy-5-iodobenzoic acid was 87percent, and crystal purity thereof was 99.7percent.
Thats from this patent: http://v3.espacenet.com/publicationDetails/biblio?CC=EP&NR=2199271&KC=&FT=E
Next we need to activate the arene...there was some work done a very long time ago (1896) where they did the same reaction I mentioned above and got the reaction to go with bromine. So I suggest you could use similar conditions to put an iodine at the 5 position. Then I would do a Miyaura reaction to put a boron there (http://www.organic-chemistry.org/namedreactions/miyaura-borylation-reaction.shtm
) and then finally couple the two pieces via a suzuki coupling. Hope that helps!