Experiments Directed Towards the Synthesis of Anthracyclinones. XV. Novel Synthetic Homochiral Chloroanthracyclines From Acetal Cyclization

Abstract

Quinizarin (3) has been converted in seven steps into the homochiral acetal (14) in 69% overall yield, through a sequence involving reductive Claisen rearrangements of the allyl ethers (8) and (20). The acetal (15) has been converted into four novel diastereomeric 9-chloroanthracyclines (31)-(34) by an unprecedented intramolecular acetal-alkene cyclization mediated by tin(IV) chloride in N,N-dimethylformamide.