Even the most famous building in Boston real estate is not immune from the foreclosure crisis. The John Hancock Tower, one of the Back Bay's most notable landmarks, is scheduled to be auctioned off to the highest bidder next month after owner, Broadway Partners, defaulted on some of its debt payments. Broadway Partners purchased the building in December 2006 for a record $1.3 billion on the speculation that red-hot Boston office rents would continue to rise. Only a last-minute deal to extend the loans on the building could prevent a foreclosure sale. It is scheduled to be auctioned on March 31st by the New York based SL Green Realty Corp.