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Schaarschmidt, Maren; Wanner, Klaus T. (2017): Synthesis of Allene Substituted Nipecotic Acids by Allenylation of Terminal Alkynes. In: Journal of Organic Chemistry, Vol. 82, No. 16: pp. 8371-8388
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The relative reactivities of several secondary amines serving, as hydride donors in propargylic amines undergoing a ,[1,5]-hydride transfer reaction to yield the respective terminal and 1,3-disubstituted allenes were Studied. For this study, a two-step procedure was employed: At first, the synthesis of propargylic amines via the Cu-I-catalyzed aldehyde-alkyne-amine reactions (A(3) coupling) was. accomplished. The obtained propargylic amines were subsequently transformed to the desired allenes under CdI2 or ZnI2 catalysis. As a result, among the various secondary amines employed, differing in steric bulk, electronic nature, and, conformational properties, allyl(tert-butyl)amine was found to be the best hydride donor for the synthesis of terminal allenes. For the synthesis of 1,3-disubstituted allenes, the, propyne derivatives containing either a allyl(tert-butyl)amine or a 1,2,3,6-tetrahydropyridine unit in propargylic position performed best. Finally, with the developed procedure nipecotic acid derivatives containing an. N-allenyl substittent were synthesized with good yields,using either ZnI2 as catalyst for the preparation of 1-substituted or CdI2-for the synthesis of 1,3-disubstitued allenes.