Two one-pot methods, sequential and tandem, for the preparation of N'-substituted 2-imino-1, 3-oxazolidines from the vicinal (sec- or tert)-amino alcohol of desosamine via intermediary alkyl-, aryl-, heteroaryl-, and heteroalkyl-thiourea moieties are described. Particularly interesting is the novel one-pot tandem reaction of the vicinal tert-amino alcohol that involves dealkylation, thiourea formation, and a final cyclization to yield 2-imino-1, 3-oxazolidine structures. The yields of both one-pot methods are comparable to the yield of the sequential reaction. A small library of a new class of desosamine-modified 14- and 15-membered macrolides was prepared to demonstrate the variety of substituents that can be easily introduced and thus enable a huge variation of the physicochemical and hence biological properties of these new molecules.