Total syntheses of furaquinocin A, B, and E.

A modular approach to the total synthesis of furaquinocins culminated in the total syntheses of furaquinocin A, B, and E. A Pd-catalyzed dynamic kinetic asymmetric transformation (DYKAT) on carbonates derived from Baylis-Hillman adducts, followed by a reductive Heck cyclization allows the enantio- and diastereoselective construction of dihydrobenzofuran 32. Introduction of a double unsatured side chain via Horner-Wadsworth-Emmons reaction and assembly of the naphthoquinone with squaric acid based methodology leads to furaquinocin E. The use of differentially substituted squaric acid derivatives allows the synthesis of three analogues of furaquinocin E. The additional stereocenters in furaquinocin A and B can be introduced with a diastereoselective Sakurai allylation. The stereoselective elongation of the side chain is possible using cross metathesis or ring closing metathesis. The obtained late-stage intermediates were successfully transformed to furaquinocin A and B.