Natural (5′-oxoheptene-1′E,3′E-dienyl)-5,6-dihydro-2H-pyran-2-one: total synthesis and revision of its absolute configuration

The synthesis of (5′-oxoheptene-1′E,3′E-dienyl)-5,6-dihydro-2H-pyran-2-one has been performed in seven steps using four key steps: a ring-closing metathesis reaction to build up the unsaturated lactone, a Wittig reaction to control the C6–C7 (E) double bond, a cross-metathesis reaction to control the (E) double bond at C8–C9, and an enantioselective allyltitanation to control the absolute configuration at C5. Spectroscopic data (IR, MS, 1H, and 13C NMR) were identical to those of the natural compound except for the optical rotation, which led us to re-assign the absolute configuration of the natural product.