if you book LH flight#, and flying LH metal, 'D' fares can be upgraded to first-class using miles&more miles or milres&more vouchers (but only very few first-class seats are given away as confirmed upgrades/award-seats in advance).

I did upgrade several 'D' fares to first in the past two years with LH (from/to Asia, also from/to SFO, from /to Europe).