[taurean]

If you could clarify just a little bit, what carboxylic acid would you compare this enol-ester with (since you are asking about equivalency)?  I think that will help eliminate the confusion that seems to be going on here.  So, you want to compare R-C(OH)=CH-C(=O)-OEt with...____________ (fill in your carboxylic acid)

Basically, I'm trying to eliminate whether the enol part of your question is important.  Are you asking if an ester can be functionally equivalent to a carboxylic acid?

My question is whether my enol is reactive towards borane as carboxylic acids does.

It could be any carboxylic acid.....suppose formic acid.

Sorry for the confusion.