Intramolecular Coupling Reactions of Allylic Thioesters with Diene Iron Tricarbonyl Systems

Cyclization reactions are reported for a series of allylic thioester derivatives of cyclohexadiene iron tricarbonyl systems, leading to the formation of spiro thialactone derivatives. The overall reaction process is equivalent to a [6π + 2π] ene reaction in which the pendant alkene, derived from the allyl thioester, is coupled with the diene of the diene−Fe(CO) 3 moiety. While simple substrates were found to undergo this cyclization readily, increased substitution on the pendant double bond led to lower, or zero, yields. Methodology for ring opening of the product thialactones, with or without reductive extrusion of sulfur, is described. The X-ray structure of one of the products ( 21b ) is reported: C 15 H 14 FeO 4, M r = 346.17. Crystal dimensions: 0.20 × 0.20 × 0.10 mm. Yelow, clear prism. Mo Kα radiation (λ = 0.71073 Å). Monoclinic space group P 2(1)/n; a = 11.355(2) Å, b = 6.4943(13) Å, c = 20.060(4) Å, β = 103.30(3)°, V = 1439.6 (5) Å 3 . Z = 4. ϑ = 2.35−27.06°. T = 150 (2) K.