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Direct conversion of the a-hydroxyl group by para-toluenesulfonamide to yield a-(N-tosyl)aminophosphonates is reported. a-Aminophosphonates 23a,b-37a,b were obtained from the corresponding a-hydroxyphosphonates 6a,b-21a,b in the presence of K 2 CO 3 , via the retro-Abramov reaction of the appropriate aldehydes, 1-5. The subsequent formation of imines with simultaneous addition of diethyl phosphite provided access to the a-sulfonamide phosphonates 23a,b-37a,b with better diastereoselectivity than in the case of the Pudovik reaction. The mechanism for this transformation is proposed herein. When Cbz N-protected aziridine 9a,b and phenylalanine analogue 12a,b were exploited, intramolecular substitution was observed, leading to the corresponding epoxide 38 as the sole product, or oxazolidin-2-one 39 as a minor product. Analogous substitution was not observed in the case of proline 18a,b and serine 21a,b derivatives.