Enantioselective Formal Total Synthesis of Damsin

Abstract

Enantioselective formal total synthesis of damsin, which was isolated from Compositae Ambrosia maritima L., is described. The highly enantio- and diastereoselective catalytic Mukaiyama-Michael reaction and subsequent highly stereoselective epimerization shorten the synthetic steps. It is also reported that the enolate, which was formed by the reaction of β-keto sulfone with lithium naphthaenide, reacted with methyl cyanoformate to form a quaternary stereogenic center in high yield with high stereoselectivity. This finding extends the synthetic chemistry starting from β-keto sulfones.

Preparation of New Chiral Building Blocks by a Mukaiyama–Michael Reaction of 2-(Phenylsulfonyl)cyclopent-2-en-1-one

“…As shown in Scheme 3 , ent - 10 , which is the enantiomer of 10 and includes structure 1a , was successfully used in our enantioselective formal total synthesis of damsin 19 because ent -10 could be synthesized by using the enantiomer of ligand L3 . In that enantioselective formal total synthesis, the β-ketosulfone 11 , which was derived from ent -10 , was effectively used for the stereoselective construction of the quaternary asymmetric carbon.…”