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Diastereoselective Strecker reactions based on (R)-phenylglycine amide as chiral auxiliary are reported. The Strecker reaction is accompanied by an in situ crystallization-induced asymmetric transformation, whereby one diastereomer selectively precipitates and can be isolated in 76−93% yield and dr > 99/1. The diastereomerically pure r-amino nitrile obtained from pivaldehyde (R 1 ) t-Bu, R 2 ) H) was converted in three steps to (S)-tert-leucine in 73% yield and >98% ee.

Palladium-catalyzed transprotection of allyloxycarbonyl-protected amines: efficient one pot formation of amides and dipeptides Roos, E.C.; Bernabe, P.; Hiemstra, H.; Speckamp, W.N.; Kaptein, B.; Boesten, W.H.J. Published in:Journal of Organic Chemistry DOI:10.1021/jo00111a035Link to publication Citation for published version (APA):Roos, E. C., Bernabe, P., Hiemstra, H., Speckamp, W. N., Kaptein, B., & Boesten, W. H. J. (1995). Palladiumcatalyzed transprotection of allyloxycarbonyl-protected amines: efficient one pot formation of amides and dipeptides. Journal of Organic Chemistry, 60, 1733-1740. DOI: 10.1021/jo00111a035 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The synthetic utility of the N4allyloxycarbonyl) (Alloc) substituent in a-amino acid derivatives is substantially extended beyond its well-known function as an amine protecting group. When the palladium-catalyzed deprotection is carried out by using tributyltin hydride as nucleophile (the Guibe method) in the presence of an active acylating agent a new acyl group is introduced on nitrogen. Successful acylating agents include carboxylic acid anhydrides, acid chlorides, and activated esters. A useful example of this methodology is the removal of the Alloc group in the presence of tert-butyl dicarbonate, which in essence amounts to a "transprotection" to a Boc-protected a-amino acid derivative. More importantly, the use of activated N-protected a-amino ester derivatives (e.g., pentafluorophenyl esters) leads to dipeptides. This new method for peptide coupling proceeds very fast under mild conditions, in good to excellent yields, and without noticeable racemization. IntroductionAn important feature of synthetic organic chemistry is the choice of a proper protecting group, which allows various synthetic operations while leaving the protected functionality in the molecule intact. Nevertheless, it can be required in certain synthetic sequences to change protecting groups, for reasons of stability and reactivity. Therefore, the availability of methodologies to transform one protecting group into another one in a mild, straightforward, and preferably, one-pot procedure is of high potential interest.The protecting groups that are probably most frequently used for amino groups are the carbamates. Carbamates uti...

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