WITH t AS
(
SELECT 111 a, 222 b FROM dual
UNION ALL SELECT 222, 333 FROM dual
UNION ALL SELECT 333, 444 FROM dual
UNION ALL SELECT 555, 666 FROM dual
UNION ALL SELECT 666, 777 FROM dual
UNION ALL SELECT 777, 888 FROM dual
)
SELECT MIN(a) a
     , MAX(b) b
  FROM (SELECT a, b
             , SUM(flag) OVER(ORDER BY a) grp
          FROM (SELECT a, b
                     , DECODE(a, LAG(b) OVER(ORDER BY a), 0, 1) flag
                  FROM t
                )
        )
 GROUP BY grp
 ORDER BY grp
;