A New Method of Synthesis of 6‐Substituted Piperidine‐2,4‐diones from Homoallylaminesстатья
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Дата последнего поиска статьи во внешних источниках: 2 октября 2018 г.
Аннотация:Mono‐ and dihomoallylamines serve as convenient precursors for the preparation of 6‐substituted piperidine‐2,4‐diones. This transformation is based, on the one hand, on a simple and well‐known halocyclocarbamation reaction proceeding by the addition of a source of cationic halogen to the N‐Boc‐protected homoallylamines and, on the other, on a new enolate‐isocyanate rearrangement that proceeds by the action of strong bases on bromocyclocarbamates. A set of racemic dihomoallylamines were prepared by the allylboration of nitriles or primary amides with triallylborane and enantiomerically enriched N‐Boc‐1‐phenyl‐3‐butenylamine was synthesized by the addition of (–)‐AllB(Ipc)2 to the corresponding silylimine. Chiral precursors containing a carboxylic ester group were synthesized from (S)‐allylglycine and‐alanine. The reactions of N‐Boc derivatives with NBS smoothly produced the corresponding bromocyclocarbamates either in the form of a single diastereomer or as an isomeric mixture. All these bromourethanes were cleanly transformed into 6‐substituted piperidine‐2,4‐diones in good yields via the formation of intermediate cyclic enolates, which was confirmed by the direct synthesis of enolate 12 and its transformation into dione 8 in a series of kinetic experiments. Based on the experimental results, a mechanism for the new enolate‐isocyanate rearrangement is proposed.