create table grp_test (col_1 number, col_2 number);

insert into grp_test values (1, 1);
insert into grp_test values (2, 1);
insert into grp_test values (3, 1);
insert into grp_test values (4, 2);
insert into grp_test values (5, 2);
insert into grp_test values (6, 1);
insert into grp_test values (7, 1);

select col_2
      ,grp_start
      ,grp_end
from  (select col_1
             ,col_2
             ,case when col_2 != prev_col_2 then col_1 else null end grp_start
             ,nvl(lead(case when col_2 != next_col_2 then col_1 else null end,1,col_1) over (order by col_1)
                 ,case when col_2 != next_col_2 then col_1 else null end) grp_end

       from  (select col_1
                    ,col_2
                    ,lag(col_2,1,-1) over (order by col_1) prev_col_2
                    ,lead(col_2,1,-1) over (order by col_1) next_col_2
              from grp_test)
       where prev_col_2 != next_col_2)
where grp_start is not null;

     COL_2  GRP_START    GRP_END
---------- ---------- ----------
         1          1          3
         2          4          5
         1          6          7

  1  select col_2, min(col_1) grp_start, max(col_1) grp_end
  2  from
  3  (
  4  select col_1, col_2, max(grp_id) over(order by col_1) max_grp_id
  5  from
  6   (
  7    select col_1, col_2,
  8           case when
  9                    rownum = 1 or col_2 != lag(col_2) over(order by col_1)
 10                then rownum
 11           end grp_id
 12     from
 13     grp_test
 14    )
 15  )
 16* group by col_2, max_grp_id
SQL> /

     COL_2  GRP_START    GRP_END
---------- ---------- ----------
         1          1          3
         1          6          7
         2          4          5