Total Syntheses of (+)- and (−)-Tetrapetalones A and C

Described
herein are syntheses of the naturally occurring polyketides
(−)-tetrapetalones A and C and their respective enantiomers.
The employed strategy involves initial assembly of a masked N-aryl tetramic acid which is advanced via a highly selective
conjugate addition/intramolecular Friedel–Crafts acylation
sequence to deliver a key azepine intermediate. Application of recently
developed C–H activation chemistry and subsequent Heck cyclization
delivers the aglycone framework in an overall 12 steps. Resolution
of the aglycone via stereospecific glycosylation with an enantiopure
glycosyl donor followed by separation of the derived diastereomers
enables further advancement to either (+)- or (−)-tetrapetalones
A and C.