Synthesis of C_2- symmetric α, α'-disubstituted azacycloalkanes as chiral building blocks and their application

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Recently, C_2 symmetric chiral compounds have been recognized as chiral auxiliary and chiral building block. Therefore, considerable effort has been directed toward synthesizing them. It is known double asymmetric reaction of achiral symmetric and bifunctionalized substrate provided C_2 symmetric chiral compounds accompanied with enantiomeric enhancements. We explored a novel C_2 symmetric 2, 6-diallylpiperidine as a chiral building block via the double asymmetric allylboration of 1, 6-heptadiene followed by aminocyclization and carbamation. Its synthetic utility has been demonstrated in the expedient synthesis of piperidine-related alkaloids such as of 2, 6-trans-dialkylpiperidines such as (-)-epi-dihydropinidine, a constituent of pine and spruce species, and (2R, 6R)-trans-solenopsin A, a constituent of fire-ant venom, precoccinelline, a ladybug defense alkaloid, and (-) porantheridine, a novel tricyclic alkaloid of Poranthera corymbosa, based on distinctive desymmetrization using iodocarbamation as a key step, along with the protection of one allyl group. Further application of this procedure to other alkaloids such as (-)-lythrandine is currently under investigation.