1) On the opposite side of the 1 x 6 or on the inside of the board, cut a series of kerf cuts with your circular saw. Cut them about 1 inch apart and about 1/4 inch deep. The 1 x 6 should not be pine or any soft wood as the kerf cuts and the bending will eventually break the board. The longer the board the easier it will be to bend. shorter boards you may have to cut the kerfs closer and possibly deeper. Each kerf cut must be the same dept and the same distance apart.
2) The way the old timer ship builders used to bend wood around the structure for the ship's hull was a forced bend with water and weights. This process takes a long time, but there are not any cuts and the board is under attitional stress each couple of days.
For example on how to do this would be. Get a barrel or nail keg or something round that you can use as a mold. Set a pre soaked 1 x 6 on this barrell's side and center it over the drum. Then position several bricks or weights on each end of the board. the weights must be the same weight and position. Periodically add more weights as you add water to the board. What you are creating is a controlled warping of the board. Once the bend is near the size you need, you can cut some kerfs if needed or force it over.