"Erhard maintains that he had a clear business purpose for engaging in the transactions because he desired to terminate his relationship with Margolis... However, even if Erhard had a legitimate business purpose for terminating his relationship with Margolis, that did not give him a business purpose for engaging in the specific transactions at issue here. The fact that he may have had a good business reason for separating from Margolis does not necessarily justify resorting to circular money movements (that just happened to create tax benefits) to effectuate that separation."