This should return the collection containing single list:
dataFrame.select("YOUR_COLUMN_NAME").rdd.map(r => r(0)).collect()
Without doing mapping, you will just get a Row object, which contains every column from the database.
This will probably get you a list of Any type. And if for specifying the result type, use .asInstanceOf[YOUR_TYPE] in (r => r(0).asInstanceOf[YOUR_TYPE]) mapping.