syntax variable question

Hi, Im trying to get a variable passed , something is obviously wrong as every combination I've tried failed.
Any suggestions for this simple syntax ?

set serveroutput on
DECLARE
ranon varchar2(14);
BEGIN
select to_char(sysdate, 'YYYYMMDDHH24MISS')INTO ranon from dual; execute immediate 'ALTER DATABASE backup CONTROLFILE to trace as '||ranon||'ctl';
-- DBMS_OUTPUT.PUT_LINE(ranon);
END;
/

sorry I dont post much, I lurk ;-)

thanks!
bob

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