A practical and efficient synthesis of the C-16-C-28 spiroketal fragment (CD) of the spongistatins.
A practical and efficient route to the CD spiroketal (C-16-C-28) of the spongistatins is reported. Two stereocenters are introduced from chiral building blocks with the remainder introduced by substrate-controlled transformations. The key beta-keto-1,3-dithiane intermediate is generated by a dithiol conjugate addition to an ynone and the 1,3-dithiane unit in the C-ring plays a key role in the spiroketalization and subsequent epimerization. The synthesis requires 24 steps, with a longest linear sequence of 19 steps in an overall yield of 14.5% (for the longest linear sequence). [reaction: see text]
Gaunt
Matthew J
MJ
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Hook
David F
DF
Tanner
Huw R
HR
Ley
Steven V
SV