The crude product generated in a reaction between N-tosyl valine and borane was studied by electrospray mass spectrometry (ESIMS). Intermediates in the formation of N-tosyl-1,3,2-oxazaborolidin-5-one 1a and further reactions of 1a were studied with negative ion mode. According to the results 1a may, as soon as it is generated, react with the starting amino acid.
Mansikka, T., Nevalainen, V., Simpura, I., Kokkonen, J., & Kostiainen, R. (1999). A study on the formation of N-tosyl-1,3,2-oxazaborolidin-5-one by electrospray mass spectrometry. Tetrahedron: Asymmetry, 10(8), 1437-1439. https://doi.org/10.1016/S0957-4166(99)00107-X