Recently, I had seen a video where a Coke was boiled, and end result was tar like substance. I am just curious to know if anyone has tried boiling beer, and what is the result?
Well, I never tried such an heresy, but theoretically you will end up with some kind of syrup (or broth, I really don't know the most appropriate word in english for it), thick, and more or less sweet depending on the beer you use. Some beers have more residual sugars than other ones.
Alcohol will be the first to evaporate, then water, which is basically the majority of beers composition, in volume, leaving behind sugars and proteins, basically. Those last compounds can be modified or merged, as well, I can't say. Then, depending on the beer's malt bill (pale, crystal, caramelized, roasted, smoked, etc), you might get different flavors related to it. I don't know what would happen to hop compounds when boiled for a long time, but you'll probably still get some bitterness from them.
You know what, you question got me curious about how it would taste at the end. =P
Beer reductions can make very good sauces. For more flavor you go with darker beers, but you apparently want to shy away from using hoppy beers because the bitterness can become rather harsh. Just punch in something like "beer reduction" into your favorite search engine.
Beer will evaporate down when boiled. During this it will become thicker. The alcohol will evaporate the quickest, then the water. Caramelization (Maillard reaction) will occur. The bitterness will NOT evaporate, making the bitterness more concentrated.
However; boiling wort is "required" to make beer and excessive boiling is used in some styles to give it extra flavours and colours or to make the resulting beer stronger.