Total
synthesis of both enantiomers of (−)-(2S,3R,6S)- and (+)-(2R,3S,6R)-microgrewiapine A along
with (+)-microcosamine A and (−)-6-epi-microgrewiapine
A from chiral 1-(α-methylbenzyl)-aziridine-2-carboxylate was
accomplished for the first time. Key steps involved in this synthesis
include one-pot reductive ring-opening of aziridine, debenzylation,
intramolecular N-alkylation to obtain the key piperidine
ring, and Julia–Kociensky olefination. The absolute configuration
of natural microgrewiapine A is assigned as (+)-(2R,3S,6R), which is opposite to the
originally proposed structure by comparing optical rotation data of
both synthetic enantiomers.