There are some errors in your request, as shown in this documentation you have to create a request compatible the the following curl sample:
curl -X POST https://us.battle.net/oauth/token
-u <developer client id>:<developer secret>
-d redirect_uri=<redirect URI used in authorize request>
-d scope=<space separated scopes>
-d grant_type=authorization_code
-d code=<authorization code>
If you are not familiar with curl, you should read curl documentation. OAuth2 RFC is another source of information.
Other useful material: