I actually have a 220 volt 50 amp extention cord. It's on a big reel with wheels and everything. As far as I can determine, the previous homeowner used it to arc weld various and sundry things around the property from a single 50 amp range-type outlet in the main workshop.
However, back to the dryer extension cord. Bad idea, IMHO. Better to have a real dryer outlet (and circuit and breaker) installed in the garage. Electric dyers draw a lot of current and the longer you make their connection, the more voltage drop that will occur, to the point where the wiring may get hot and/or the dryer suffer from low voltage problems.
The 220 to 110 volt conversion adapter would of course be another matter.