Synthesis of nearly enantiopure allylic amines by aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates catalyzed by highly active ferrocenylbispalladacycles.
The development of the first highly active enantioselective catalyst for the aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates generating valuable almost enantiopure protected allylic amines is described. Usually Z-configured allylic imidates react significantly slower than their E-configured counterparts, but in the present study the opposite effect was observed. Z-Configured olefins have the principal practical advantage that a geometrically pure C=C double bond can be readily obtained, for example, by semihydrogenations of alkynes. Our catalyst, a C(2)-symmetric planar chiral bispalladacycle complex, is rapidly prepared from ferrocene in four simple steps. Key step of this protocol is an unprecedented highly diastereoselective biscyclopalladation providing dimeric macrocyclic complexes of fascinating structure. In the present study as little as 0.1 mol % of catalyst precursor were sufficient for most of the alkyl substituted substrates to give in general almost quantitative yields. NMR investigations revealed a monomeric structure for the active catalyst species. The bispalladacycle can also be used for the formation of almost enantiomerically pure allylic amines (ee > or =96 %) substituted with important functional groups such as ester, ketone, ether, silyl ether, acetal or protected amino moieties providing high-added-value allylic amine building blocks in excellent yield (> or =94 %). The preparative advantages should render this methodology highly appealing as a practical and valuable tool for the formation of allylic amines in target oriented synthesis.
D000498:Allyl Compounds / Q000138:chemical synthesis*; D000588:Amines / Q000138:chemical synthesis*; D001372:Aza Compounds / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D005296:Ferrous Compounds / Q000737:chemistry*; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D048288:Imidazolines / Q000737:chemistry; D007096:Imidoesters / Q000737:chemistry*; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism
D000498:Allyl Compounds; D000588:Amines; D001372:Aza Compounds; D005296:Ferrous Compounds; D006845:Hydrocarbons, Fluorinated; D048288:Imidazolines; D007096:Imidoesters; D009942:Organometallic Compounds; D010165:Palladium; D002244:Carbon