Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_23235767_4 ( year VARCHAR, opponent_in_the_final VARCHAR, surface VARCHAR, championship VARCHAR )

### Question ###
Name the year for clay for boston and guillermo vilas

### Accurate SQL ###

SELECT year FROM table_23235767_4 WHERE surface = "Clay" AND championship = "Boston" AND opponent_in_the_final = "Guillermo Vilas"